Title of Invention	ANTENNA DEVICE AND WIRELESS COMMUNICATION APPARATUS
Abstract	An antenna device and a wireless communication apparatus that are capable of obtaining a plurality of resonant frequencies and varying the plurality of resonant frequencies over a wide range are provided. A first antenna unit 2 of an antenna device 1 includes a feed electrode 4, a first radiation electrode 5, and a first frequency-variable circuit 6-1. The first frequency-variable circuit 6-1 includes first and second reactance circuits 6A and 6B each including a variable-capacitance diode. A control voltage Vc is applied to the first frequency-variable circuit 6-1, and the resonant frequency of the first antenna unit 2 can thus be varied. A second antenna unit 3 includes the feed electrode 4, a second radiation electrode 7, and a second frequency-variable circuit 6-2. The second frequency-variable circuit 6-2 includes first and third reactance circuits 6A and 6C each including a variable-capacitance diode. A control voltage Vc is applied to the second frequency-variable circuit 6-2, and the resonant frequency of the second antenna unit 3 can thus be varied.

Title of Invention

ANTENNA DEVICE AND WIRELESS COMMUNICATION APPARATUS

Abstract

An antenna device and a wireless communication apparatus that are capable of obtaining a plurality of resonant frequencies and varying the plurality of resonant frequencies over a wide range are provided. A first antenna unit 2 of an antenna device 1 includes a feed electrode 4, a first radiation electrode 5, and a first frequency-variable circuit 6-1. The first frequency-variable circuit 6-1 includes first and second reactance circuits 6A and 6B each including a variable-capacitance diode. A control voltage Vc is applied to the first frequency-variable circuit 6-1, and the resonant frequency of the first antenna unit 2 can thus be varied. A second antenna unit 3 includes the feed electrode 4, a second radiation electrode 7, and a second frequency-variable circuit 6-2. The second frequency-variable circuit 6-2 includes first and third reactance circuits 6A and 6C each including a variable-capacitance diode. A control voltage Vc is applied to the second frequency-variable circuit 6-2, and the resonant frequency of the second antenna unit 3 can thus be varied.

Full Text	DESCRIPTION ANTENNA DEVICE AND WIRELESS COMMUNICATION APPARATUS Technical Field The present invention relates to an antenna device and a wireless communication apparatus that are capable of varying a resonant frequency over a certain range. Background Art As an antenna device of this type, for example, a frequency-variable antenna disclosed in Patent Document 1 has been available. The antenna device has a configuration in which a feed electrode and a single radiation electrode are formed on a substrate and a single frequency-variable circuit is disposed between the feed electrode and the radiation electrode. With this configuration, varying a control voltage to be applied to a variable-capacitance diode contained in the frequency-variable circuit varies a resonant frequency of the antenna. Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-060384 Disclosure of Invention However, the above-described antenna device has the problems described below. Since the antenna device includes a feed electrode, a frequency-variable circuit, and a single radiation electrode, only a single resonant frequency can be obtained. In addition, although the resonant frequency can be varied using the frequency-variable circuit, since the frequency-variable circuit, which has only a single variable-capacitance diode, is used, the resonant frequency cannot be varied over a wide range. In order to solve the above-mentioned problems, an object of the present invention is to provide an antenna device and a wireless communication apparatus that are capable of obtaining a plurality of resonant frequencies and varying the plurality of resonant frequencies over a wide range. In order to solve the above-mentioned problems, according to the invention of Claim 1, an antenna device includes a first antenna unit including a feed electrode connected to a feed unit, a first radiation electrode, and a first frequency-variable circuit connected between the first radiation electrode and the feed electrode; and a second antenna unit including the feed electrode, a second radiation electrode, and a second frequency-variable circuit connected between the second radiation electrode and the feed electrode. The first frequency-variable circuit includes a first reactance circuit connected to the feed electrode, the first reactance circuit including a first variable-capacitance diode whose capacitance is variable using a control voltage; and a second reactance circuit connected between the first reactance circuit and the first radiation electrode, the second reactance circuit including a second variable-capacitance diode whose capacitance is variable using the control voltage. The second frequency-variable circuit includes the first reactance circuit; and a third reactance circuit connected between the first reactance circuit and the second radiation electrode, the third reactance circuit including a third variable-capacitance diode whose capacitance is variable using the control voltage. With this configuration, when electric power is supplied from the feed unit to the feed electrode, the first antenna unit resonates with electric power at a frequency and transmits an electric wave at the frequency. In addition, the second antenna unit resonates with electric power at a frequency that is different from the resonant frequency of the first antenna unit and transmits an electric wave at the different frequency. That is, the antenna device according to the present invention is capable of achieving a two-resonant state exhibiting a resonant frequency of the first antenna unit and a resonant frequency of the second antenna unit. In addition, since the capacitance of the second variable-capacitance diode of the second reactance circuit, as well as the capacitance of the first variable-capacitance diode of the first reactance circuit, can be varied using a control voltage, a large reactance change for two variable-capacitance diodes can be achieved by the first frequency-variable circuit. As a result, the resonant frequency of the first antenna unit can be varied over a wide range. In addition, since the capacitance of the first variable-capacitance diode of the first reactance circuit and the capacitance of the third variable-capacitance diode of the third reactance circuit are controlled using the control voltage, a large reactance change for two variable-capacitance diodes can be achieved by the second frequency-variable circuit. As a result, the resonant frequency of the second antenna unit can also be varied over a wide range. According to the invention of Claim 2, in the antenna device according to Claim 1, the second variable-capacitance diode of the second reactance circuit and the third variable-capacitance diode of the third reactance circuit may be disposed so as to associate with the first variable-capacitance diode of the first reactance circuit, cathodes of the first to third variable-capacitance diodes may be connected to each other, and the control voltage may be applied to a portion where the cathodes are connected to each other. With this configuration, the three variable-capacitance diodes of the first to third variable-capacitance diodes can be varied at the same time using the control voltage. According to the invention of Claim 3, in the antenna device according to Claim 1 or 2, the first reactance circuit may be a series resonant circuit or a parallel resonant circuit including the first variable-capacitance diode, the second reactance circuit may be a series resonant circuit or a parallel resonant circuit including the second variable-capacitance diode, and the third reactance circuit may be a series resonant circuit or a parallel resonant circuit including the third variable-capacitance diode. With this configuration, when all the first to third reactance circuits are configured as series resonant circuits, a large gain can be obtained without greatly increasing variable ranges of the resonant frequency of the first antenna unit and the resonant frequency of the second antenna unit. When all the first to third reactance circuits are configured as parallel resonant circuits, variable ranges of the resonant frequency of the first antenna unit and the resonant frequency of the second antenna unit can be increased although a large gain is not obtained Thus, when at least one of the first to third reactance circuits is configured as a series resonant circuit and the others of the first to third reactance circuits are configured as parallel resonant circuits, the amount of change in the resonant frequency of the first antenna unit can be made different from the amount of change in the resonant frequency of the second antenna unit. According to the invention of Claim 4, in the antenna device according to Claim 3, each of the first to third reactance circuits may be configured as a parallel resonant circuit in which a coil is connected in parallel to a series circuit including the corresponding variable-capacitance diode, and at least one of the coils of the first to third reactance circuits may be set as a choke coil and the corresponding reactance circuit including the coil may serve substantially as a series resonant circuit. With this configuration, when the coil of the parallel resonant circuit is used as a choke coil, a reactance circuit including the coil is substantially capable of serving as a series resonant circuit. Thus, design can be easily changed without requiring reconfiguration of a parallel resonant circuit portion into a series resonant circuit. According to the invention of Claim 5, in the antenna device according to any one of Claims 1 to 4, an internal resistance of at least one of the first to third variable-capacitance diodes may be different from internal resistances of the others of the first to third variable-capacitance diodes. When the internal resistance of a variable-capacitance diode is reduced, although a gain is increased, a variable-capacitance range becomes narrower. In contrast, when the internal resistance is increased, although a gain is reduced, a variable capacitance range becomes wider. Thus, with this configuration, when the internal resistance of at least one of the first to third variable-capacitance diodes is made different from the internal resistances of the others of the first to third variable-capacitance diodes while considering which of a frequency variable range or a gain is to be emphasized, characteristics of the first antenna unit and the second antenna unit can be obtained according to the situation. According to the invention of Claim 6, in the antenna device according to any one of Claims 1 to 5, at least the first antenna unit may be formed on a dielectric substrate. With this configuration, the capacitance of at least the first antenna unit can be increased, and the reactance of the first antenna unit can be increased. According to the invention of Claim 7, in the antenna device according to any one of Claims 1 to 6, an additional radiation electrode may be connected to a stage subsequent to the first reactance circuit, which is connected to the feed electrode, and an additional antenna unit may be formed by the additional radiation electrode, the feed electrode, and the first reactance circuit, which is a frequency-variable circuit. With this configuration, the resonant frequency of the additional antenna unit, as well as the resonant frequencies of the first and second antenna units, can be obtained. Thus, electric waves of more resonant frequencies can be handled. In addition, the resonant frequencies of the first and second antenna unit and the resonant frequency of the additional antenna unit can be varied at the same time. According to the invention of Claim 8, in the antenna device according to any one of Claims 1 to 7, a plurality of additional antenna units may be provided, and in at least one of the plurality of additional antenna units, an additional reactance circuit including a variable-capacitance diode whose capacitance is variable using the control voltage may be connected between the first reactance circuit and the corresponding additional radiation electrode, and a frequency-variable circuit of the at least one of the plurality of additional antenna units may be formed by the additional reactance circuit and the first reactance circuit. With this configuration, since the frequency-variable circuit of the additional antenna unit is formed by the additional reactance circuit and the first reactance circuit, the resonant frequency of the additional antenna unit can be varied over a wide range. A wireless communication apparatus according to Claim 9 includes the antenna device according to any one of Claims 1 to 8. As described above, since the antenna device according to the present invention includes a plurality of antenna units, an excellent advantage of obtaining a plurality of resonant frequencies can be achieved. Moreover, since a frequency-variable circuit of each of the plurality of antenna units includes two reactance circuits each including a variable-capacitance diode, a large reactance change for two variable-capacitance diodes can be achieved. As a result, the resonant frequency of each of the plurality of antenna units can be varied over a wider range. In addition, in the antenna device according to the invention of Claim 3, a large gain can be obtained when all the first to third reactance circuits are configured as series resonant circuit, and a wide variable range of a resonant frequency can be achieved when all the first to third reactance circuits are configured as parallel resonant circuits . When both a series resonant circuit and a parallel resonant circuit are used, the amount of change in the resonant frequency and the gain of the first antenna unit can be made different from the amount of change in the resonant frequency and the gain of the second antenna unit. As a result, optimal characteristics can be achieved according to the use state. In addition, in the antenna device according to the invention of Claim 4, there is no need to reconfigure a parallel resonant circuit portion into a series resonant circuit. Thus, a design change from a parallel resonant circuit into a series resonant circuit can be performed easily. In addition, in the antenna device according to the invention of Claim 5, characteristics of the first antenna unit and the second antenna unit can be obtained according to the situation. In addition, in the antenna device according to claim 6, the reactance of at least the first antenna unit can be increased. Thus, the resonant frequency of the first antenna unit can be reduced. In addition, in the antenna device according to the invention of Claim 7, a larger number of resonances can be obtained Moreover, the resonant frequencies can be varied at the same time. In particular, according to the invention of Claim 8, the resonant frequencies of the additional antenna units can be varied over a wide range. In addition, in the wireless communication apparatus according to the invention of Claim 9, transmission and reception can be performed such that a frequency change can be achieved over a wide range for multi-resonances. Brief Description of the Drawings Fig. 1 is a schematic plan view showing an antenna device according to a first embodiment of the present invention. Fig. 2 is a chart illustrating a variable state of two resonances. Fig. 3 is a schematic plan view showing an antenna device according to a second embodiment of the present invention. Fig. 4 is a chart illustrating a variable state of two resonances. Fig. 5 is a schematic plan view showing an antenna device according to a third embodiment of the present invention. Fig. 6 is a chart illustrating a variable state of two resonances. Fig. 7 is a schematic plan view showing an antenna device according to a fourth embodiment of the present invention. Fig. 8 is a chart illustrating a variable state of two resonances. Fig. 9 is a schematic plan view showing an antenna device according to a fifth embodiment of the present invention. Fig. 10 is a chart illustrating a variable state of two resonances. Fig. 11 is a schematic plan view showing an antenna device according to a sixth embodiment of the present invention. Fig. 12 is a chart illustrating the relationship between a frequency and a gain when a variable-capacitance diode has a large internal resistance. Fig. 13 is a chart illustrating the relationship between a frequency and a gain when a variable-capacitance diode has a small internal resistance. Fig. 14 is a perspective view showing an antenna device according to a seventh embodiment of the present invention. Fig. 15 is a schematic plan view showing an antenna device according to an eighth embodiment of the present invention. Fig. 16 is a chart illustrating a variable state of multi-resonances. Fig. 17 is a schematic plan view showing an antenna device according to a ninth embodiment of the present invention. Fig. 18 is a chart illustrating a variable state of multi-resonances. Reference Numerals 1: antenna device, 2: first antenna unit, 3: second antenna unit, 3-1 to 3-n: additional antenna unit, 4: feed electrode, 5: first radiation electrode, 6-1: first frequency-variable circuit, 6-2: second frequency-variable circuit, 6A: first reactance circuit, 6B: second reactance circuit, 6C: third reactance circuit, 6D and 6E: additional reactance circuit, 7: second radiation electrode, 8: dielectric substrate, 9 and 9-1 to 9-n: additional radiation electrode, 50: open end, 51, 71, and 91: ground coil, 61A: first variable-capacitance diode, 61B: second variable-capacitance diode, 61C: third variable-capacitance diode, 61D and 61E: variable-capacitance diode, 62A, 62B, 62C, 63A, 63B, and 63C: coil, 64: common capacitor, 100: circuit board, 101: non-ground region, 102: ground region, 110: transmitter/receiver, 120: reception-frequency controller, G: gap, P: connection point, S1: return-loss curve, S2: return-loss curve, Vc: control voltage, dl, d2, d3, d4, • • • and dn: amount of change, f1, f2, f3, f4, ••• and fn: resonant frequency Best Mode for Carrying Out the Invention The best mode for carrying out the present invention will be described with reference to the drawings. First Embodiment Fig. 1 is a schematic plan view showing an antenna device according to a first embodiment of the present invention. An antenna device 1 according to this embodiment is provided in a wireless communication apparatus, such as a cellular phone. As shown in Fig. 1, the antenna device 1 is formed in a non-ground region 101 of a circuit board 100 of the wireless communication apparatus. The antenna device 1 transfers high-frequency signals to and from a transmitter/receiver 110, which is provided in a ground region 102 and serves as a power-feed unit. A reception-frequency controller 120 provided in the transmitter/receiver 110 applies a direct-current control voltage Vc to the antenna device 1. The antenna device 1 includes a first antenna unit 2 and a second antenna unit 3. The first antenna unit 2 includes a feed electrode 4, a first radiation electrode 5, and a first frequency-variable circuit 6-1 connected between the feed electrode 4 and the first radiation electrode 5. More specifically, a matching circuit including coils 111 and 112 is formed in the non-ground region 101, and the feed electrode 4, which is a conductive pattern, is connected to the transmitter/receiver 110 through the matching circuit. The first radiation electrode 5 is a conductive pattern having a loop shape. An open end 50 of the first radiation electrode 5 faces the feed electrode 4 with a gap G therebetween. The gap G causes a capacitance between the feed electrode 4 and the first radiation electrode 5. By varying the size of the gap G, the reactance of the first antenna unit 2 can be set to a desired value. A ground coil 51, which is provided for resonant frequency adjusting, is connected in the middle of the first radiation electrode 5. The first frequency-variable circuit 6-1 includes a first reactance circuit 6A (represented by "jX1" in Fig. 1) , which is connected to the feed electrode 4, and a second reactance circuit 6B (represented by "jX2" in Fig. 1), which is connected between the first reactance circuit 6A and the first radiation electrode 5. The first reactance circuit 6A includes a first variable-capacitance diode, which is not shown. When a control voltage Vc is applied to the first variable-capacitance diode, the capacitance of the first variable-capacitance diode increases or decreases, resulting in a change in the reactance of the first reactance circuit 6A. The second reactance circuit 6B includes a second variable-capacitance diode, which is not shown. When a control voltage Vc is applied to the second variable-capacitance diode, the capacitance of the second variable-capacitance diode increases or decreases, resulting in a change in the reactance of the second reactance circuit 6B. A connection point P between the first reactance circuit 6A and the second reactance circuit 6B is connected to the reception-frequency controller 120 through a high-frequency cutoff resistor 121 and a DC-pass capacitor 122. With this configuration, when the reception-frequency controller 120 applies a control voltage Vc to the connection point P, the reactances of the first and second reactance circuits 6A and 6B increase or decrease in accordance with the size of the control voltage Vc, resulting in a change in the reactance of the entire first frequency-variable circuit 6-1, as described above. That is, applying the control voltage Vc to the first frequency-variable circuit 6-1 varies the electrical length of the first antenna unit 2, thus varying the resonant frequency of the first antenna unit 2. The second antenna unit 3 includes the feed electrode 4, a second radiation electrode 7, and a second frequency-variable circuit 6-2 connected between the feed electrode 4 and the second radiation electrode 7. More specifically, the second radiation electrode 7 is a conductive pattern having a line shape. A ground coil 71, which is provided for resonant frequency adjusting, is connected to an end of the second radiation electrode 7. The second frequency-variable circuit 6-2 includes the first reactance circuit 6A and a third reactance circuit 6C (represented by "jX3" in Fig. 1) , which is connected between the first reactance circuit 6A and the second radiation electrode 7. Similarly to the first reactance circuit 6A, the third reactance circuit 6C includes a third variable-capacitance diode, which is not shown. When a control voltage Vc is applied to the third variable-capacitance diode, the capacitance of the third variable-capacitance diode increases or decreases, resulting in a change in the reactance of the third reactance circuit 6C. The third reactance circuit 6C is also connected to the connection point P between the first reactance circuit 6A and the second reactance circuit 6B. When the reception-frequency controller 120 applies a control voltage Vc to the connection point P, the reactances of the first and third reactance circuits 6A and 6C increase or decrease in accordance with the size of the control voltage Vc, resulting in a change in the reactance of the entire second frequency-variable circuit 6-2. That is, applying the control voltage Vc to the second frequency-variable circuit 6-2 varies the electrical length of the second antenna unit 3, thus varying the resonant frequency of the second antenna unit 3. Operations and advantages of the antenna device according to this embodiment will be described. Fig. 2 is a chart illustrating a variable state of two resonances. As described above, the first antenna unit 2 includes the feed electrode 4, the first frequency-variable circuit 6-1, and the first radiation electrode 5, and the second antenna unit 3 includes the feed electrode 4, the second frequency-variable circuit 6-2, and the second radiation electrode 7. With this configuration, a two-resonant state exhibiting a resonant frequency f 1 of the first antenna unit 2 and a resonant frequency f2 of the second antenna unit 3 can be achieved. For example, when the length of the first radiation electrode 5 is set to be longer than the length of the second radiation electrode 7, the resonant frequency f1 of the first antenna unit 2 is lower than the resonant frequency f2 of the second antenna unit 3. In this case, a return-loss curve S1 represented by a solid line shown in Fig. 2 is obtained. When a control voltage Vc is applied to the first frequency-variable circuit 6-1, the reactances of the first and second reactance circuits 6A and 6B increase or decrease in accordance with the size of the control voltage Vc, resulting in a change in the reactance of the entire first frequency-variable circuit 6-1. Thus, the electrical length of the first antenna unit 2 is changed, and the resonant frequency fl of the first antenna unit 2 is changed. In parallel to this, the reactances of the first and third reactance circuits 6A and 6C of the second frequency-variable circuit 6-2 also increase or decrease in accordance with the size of the control voltage Vc, resulting in a change in the reactance of the entire second frequency-variable circuit 6-2. Thus, the electrical length of the second antenna unit 3 is changed, and the resonant frequency f2 of the second antenna unit 3 is changed. As a result, as shown by a return-loss curve S2 represented by a broken line shown in Fig. 2, the resonant frequency fl of the first antenna unit 2 moves by the amount of change d1, which corresponds to the size of the control voltage Vc, and reaches a frequency f1'. At the same time, the resonant frequency f2 of the second antenna unit 3 moves by the amount of change d2, which corresponds to the size of the control voltage Vc, and reaches a frequency f2'. At this time, the amount of change d1 (d2), by which the resonant frequency f1 (f2) is changed to the resonant frequency f1' (f2') by the first frequency-variable circuit 6-1 (the second frequency-variable circuit 6-2), is obtained not only from the amount of change in the capacitance of the first variable-capacitance diode included in the first reactance circuit 6A but also from the amount of change in the capacitance of the second variable-capacitance diode (the third variable-capacitance diode) included in the second reactance circuit 6B (the third reactance circuit 6C). Thus, the large amount of change dl (d2) can be obtained. As a result, the resonant frequency fl (f2) of the first antenna unit 2 (the second antenna unit 3) can be varied over a wide range. In the antenna device of the related art, only a single resonance appears and a resonant frequency is varied by a frequency-variable circuit including only a single variable-capacitance diode. Thus, in order to vary the resonant frequency over a wide range from fl to f2', as shown in Fig. 2, a large control voltage Vc is necessary. Such an antenna device is not suitable for a wireless communication apparatus, such as a cellular phone, which requires a lower voltage specification. In contrast, in the antenna device 1 according to this embodiment, the resonant frequencies f1 and f2 in the two-resonant state can be varied at the same time by a predetermined control voltage Vc, as described above. Thus, a resonant frequency can be varied over a wide range from fl to f2' by the application of a low control voltage Vc. Thus, the antenna device 1 according to this embodiment is suitable for a wireless communication apparatus, such as a cellular phone, which requires a lower power-supply voltage. Second Embodiment A second embodiment of the present invention will be described. Fig. 3 is a schematic plan view showing an antenna device according to the second embodiment of the present invention. The antenna device according to this embodiment is provided in which a concrete series resonant circuit is applied to each of the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C used in the first embodiment. As shown in Fig. 3, the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C are configured as a series resonant circuit including a first variable-capacitance diode 61A, a series resonant circuit including a second variable-capacitance diode 61B, and a series resonant circuit including a third variable-capacitance diode 61C, respectively. More specifically, a series resonant circuit including the first variable-capacitance diode 61A and a coil 62A is used as the first reactance circuit 6A. The coil 62A is connected to the feed electrode 4. The cathode of the first variable-capacitance diode 61A is connected to the connection point P. A series resonant circuit including the second variable-capacitance diode 61B and a coil 62B is used as the second reactance circuit 6B. The coil 62B is connected to the first radiation electrode 5. The cathode of the second variable-capacitance diode 61B is connected to the connection point P. A series resonant circuit including the third variable-capacitance diode 61C and a coil 62C is used as the third reactance circuit 6C. The coil 62C is connected to the second radiation electrode 7. The cathode of the third variable-capacitance diode 61C is connected to the connection point P. That is, the second variable-capacitance diode 61B of the second reactance circuit 6B and the third variable-capacitance diode 61C of the third reactance circuit 6C are disposed so as to associate with the first variable-capacitance diode 61A of the first reactance circuit 6A. The cathodes of the first to third variable-capacitance diodes 61A to 61C are connected to each other. A control voltage Vc is applied to a portion where the cathodes are connected to each other. Operations and advantages of the antenna device according to this embodiment will be described. Fig. 4 is a chart illustrating a variable state of two resonances. As shown by a return-loss curve S1 represented by a solid line shown in Fig. 4, in the antenna device according to this embodiment, a two-resonant state exhibiting a resonant frequency f1 of the first antenna unit 2 and a resonant frequency f2 of the second antenna unit 3 can be achieved. Applying a control voltage Vc to each of the first frequency-variable circuit 6-1 and the second frequency-variable circuit 6-2 varies the resonant frequency f 1 of the first antenna unit 2 and the resonant frequency f2 of the second antenna unit 3 at the same time. In the series resonant circuit including the first variable-capacitance diode and the coil, the reactance with respect to the control voltage Vc varies substantially linearly. Thus, although the amount of change dl (d2) from the resonant frequency f1 to the resonant frequency f1' (f2 to f2') by the first frequency-variable circuit 6-1 (the second frequency-variable circuit 6-2) is not very large, a large gain can be achieved. Consequently, in a case where all the first to third reactance circuits 6A to 6C are configured as series resonant circuits as in this embodiment, an antenna device in which a gain is emphasized can be achieved. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna device according to the first embodiment, the description of those similar configurations, operations, and advantages will be omitted. Third Embodiment A third embodiment of the present invention will be described. Fig. 5 is a schematic plan view showing an antenna device according to the third embodiment of the present invention. The antenna device according to this embodiment is provided in which a concrete parallel resonant circuit is applied to each of the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C used in the first embodiment. That is, as shown in Fig. 5, the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C are configured as a parallel resonant circuit including the first variable-capacitance diode 61A, a parallel resonant circuit including the second variable-capacitance diode 61B, and a parallel resonant circuit including the third variable-capacitance diode 61C, respectively. More specifically, a parallel resonant circuit in which a series circuit including a coil 63A and a common capacitor 64 is connected in parallel to the series circuit including the first variable-capacitance diode 61A and the coil 62A is used as the first reactance circuit 6A. A parallel resonant circuit in which a series circuit including a coil 63B and the common capacitor 64 is connected in parallel to the series circuit including the second variable-capacitance diode 61B and the coil 62B is used as the second reactance circuit 6B. A parallel resonant circuit in which a coil 63C is connected in parallel to the series circuit including the third variable-capacitance diode 61C and the coil 62C is used as the third reactance circuit 6C. Operations and advantages of the antenna device according to this embodiment will be described. Fig. 6 is a chart illustrating a variable state of two resonances. As shown by a return-loss curve S1 represented by a solid line shown in Fig. 6, the antenna device according to this embodiment achieves a two-resonant state exhibiting a resonant frequency f 1 of the first antenna unit 2 and a resonant frequency f2 of the second antenna unit 3, as in the first embodiment. Applying a control voltage Vc to each of the first frequency-variable circuit 6-1 and the second frequency-variable circuit 6-2 varies the resonant frequency f 1 of the first antenna unit 2 and the resonant frequency f2 of the second antenna unit 3 at the same time. In the parallel resonant circuit in which a series circuit including a variable-capacitance diode and a coil is connected in parallel to another coil, the reactance with respect to the control voltage varies nonlinearly. Thus, although a large gain is not obtained, a significantly large amount of change d1 (d2) from the resonant frequency f1 to the resonant frequency f1' (f2 to f2') by the first frequency-variable circuit 6-1 (the second frequency-variable circuit 6-2) can be achieved. Consequently, in a case where all the first to third reactance circuits 6A to 6C are configured as parallel resonant circuits as in this embodiment, an antenna device that is capable of varying a frequency over a wide range can be achieved. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna devices according to the first and second embodiments, the description of those similar configurations, operations, and advantages will be omitted. Fourth Embodiment A fourth embodiment of the present invention will be described. Fig. 7 is a schematic plan view showing an antenna device according to the fourth embodiment of the present invention. The antenna device according to this embodiment is provided in which both a series resonant circuit and a parallel resonant circuit are applied to the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C used in the first embodiment. That is, as shown in Fig. 7, the first reactance circuit 6A and the second reactance circuit 6B are configured as a parallel resonant circuit including the first variable-capacitance diode 61A and a parallel resonant circuit including the second variable-capacitance diode 61B, respectively. The third reactance circuit 6C is configured as a series resonant circuit including the third variable-capacitance diode 61C. Operations and advantages of the antenna device according to this embodiment will be described. Fig. 8 is a chart illustrating a variable state of two resonances. As shown by a return-loss curve S1 represented by a solid line shown in Fig. 8, the antenna device according to this embodiment also achieves two resonances f 1 and f2 caused by the first and second antenna units 2 and 3. Applying a control voltage Vc to each of the first and second frequency-variable circuits 6-1 and 6-2 varies the resonant frequency f 1 of the first antenna unit 2 and the resonant frequency f2 of the second antenna unit 3 at the same time. In the first frequency-variable circuit 6-1 including the first reactance circuit 6A and the second reactance circuit 6B, which are configured as parallel resonant circuits, the reactance with respect to the control voltage Vc varies nonlinearly, as described above. Thus, although a large gain is not achieved, the amount of change d1 from the resonant frequency f1 to the resonant frequency f1' is significantly large, as shown in Fig. 8. In the third reactance circuit 6C, which is a series resonant circuit, the reactance with respect to the control voltage Vc varies linearly. Thus, although a large amount of change in the reactance is not achieved, a large gain can be obtained. As a result, the amount of change d2 from the resonant frequency f2 to the resonant frequency f2' by the second frequency-variable circuit 6-2, which includes the first reactance circuit 6A configured as a parallel resonant circuit and the third reactance circuit 6C configured as a series resonant circuit, is small. That is, according to this embodiment, an antenna device that is capable of achieving a large amount of change d1 of the resonant frequency f1 and ensuring a certain amount of change d2 of the resonant frequency f2 while obtaining a large gain can be achieved. The antenna device including the first reactance circuit 6A and the second reactance circuit 6B, which are configured as parallel resonant circuits, and the third reactance circuit 6C, which is configured as a series resonant circuit, has been explained in this embodiment. However, the present invention is not limited to this. Determination of which reactance circuit is to be configured as a parallel resonant circuit and determination of which reactance circuit is to be configured as a series resonant circuit can be performed in accordance with which of the variation width of a resonant frequency band or the gain is to be emphasized. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna devices according to the second and third embodiments, the description of those similar configurations, operations, and advantages will be omitted. Fifth Embodiment A fifth embodiment of the present invention will be described. Fig. 9 is a schematic plan view showing an antenna device according to the fifth embodiment of the present invention. Fig. 10 is a chart illustrating a variable state of two resonances. The antenna device according to this embodiment has a configuration in which both a series resonant circuit and a parallel resonant circuit are applied to the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C, as in the fourth embodiment. However, the antenna device according to this embodiment is different from the antenna device according to the fourth embodiment in that a series resonant circuit is formed using a choke coil. That is, as shown in Fig. 9, the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C are configured as parallel circuits. By using a choke coil as a coil of the second reactance circuit 6B, the second reactance circuit 6B is substantially capable of serving as a series resonant circuit. More specifically, the second reactance circuit 6B is formed by connecting a series circuit including the common capacitor 64 and a coil 63B' in parallel to the series circuit including the second variable-capacitance diode 61B and the coil 62B. The coil 63B' is set as a choke coil for cutting off electric power having an in-band frequency of the first antenna unit 2. The coil 63B' can be set as a choke coil by adjusting the inductance of the coil 63B'. That is, the second reactance circuit 6B is substantially configured so as to function as a series resonant circuit including the first variable-capacitance diode 61A and the coil 62B. With this configuration, as shown by a return-loss curve S1 represented by a solid line and a return-loss curve S2 represented by a broken line shown in Fig. 10, the first frequency-variable circuit 6-1 achieves a large gain while ensuring a certain amount of change d1 of the resonant frequency f 1 and the second frequency-variable circuit 6-2 achieves a large amount of change d2 of the resonant frequency f2. As described above, according to this embodiment, all the first to third reactance circuits 6A to 6C are designed as parallel circuits, and one of the coils 63A to 63C is set as a choke coil by adjusting the inductance of the one of the coils 63A to 63C according to the situation. Thus, a parallel circuit including the choke coil functions substantially as a series resonant circuit. Consequently, design can be changed easily without requiring reconfiguration of a parallel circuit portion into a serial resonant circuit. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna device according to the fourth embodiment, the description of those similar configurations, operations, and advantages will be omitted. Sixth Embodiment A sixth embodiment of the present invention will be described. Fig. 11 is a schematic plan view showing an antenna device according to the sixth embodiment of the present invention. In the antenna device according to this embodiment, all the first reactance circuit 6A, the second reactance circuit 6B, and the third reactance circuit 6C are configured as parallel resonant circuits, as in the third embodiment. However, the antenna device according to this embodiment is different from the antenna devices according to the third to fifth embodiments in that functions similar to functions attained in a case where a series resonant circuit and a parallel resonant circuit are applied to the first to third reactance circuits 6A to 6C can be attained by using an internal resistance of a variable-capacitance diode. Fig. 12 is a chart illustrating the relationship between the frequency and the gain when a variable-capacitance diode has a large internal resistance. Fig. 13 is a chart illustrating the relationship between the frequency and the gain when a variable-capacitance diode has a small internal resistance. Each variable-capacitance diode has an internal resistance that is characteristic of the diode. As shown in Fig. 12, the larger the internal resistance of a variable-capacitance diode is, the smaller the gain is. However, when such a variable-capacitance diode is used, a variable-capacitance range is increased. In contrast, the smaller the internal resistance is, the larger the gain is, as shown in Fig. 13. However, when such a variable-capacitance diode is used, a variable capacitance range is reduced. The antenna device according to this embodiment utilizes such characteristics of variable-capacitance diodes. The internal resistances Ra, Rb, and Re of the first variable-capacitance diode 61A, the second variable-capacitance diode 61B, and the third variable-capacitance diode 61C are set to Ra > Rb > Re. With this configuration, the first frequency-variable circuit 6-1 is capable of varying the resonant frequency f1 of the first antenna unit 2 over a wide range and the second frequency-variable circuit 6-2 is capable of varying the resonant frequency f2 over a predetermined range and obtaining a large gain. In this embodiment, the internal resistances Ra, Rb, and Re of the first variable-capacitance diode 61A, the second variable-capacitance diode 61B, and the third variable-capacitance diode 61C are set to Ra > Rb > Re. The values of the internal resistances can be determined depending on which of a frequency variable range or a gain is to be emphasized. Thus, when all the internal resistances Ra to Re are set to the same large value, the first and second frequency-variable circuits 6-1 and 6-2 are capable of achieving a wide variable range for the resonant frequencies f1 and f2. When all the internal resistances Ra to Re are set to the same small value, a large gain can be achieved in each of the first antenna unit 2 and the second antenna unit 3. In addition, when at least one of the internal resistances Ra to Re is set to be different from the others of the internal resistances Ra to Re in an appropriate manner, optimal characteristics of the first and second antenna units 2 and 3 can be achieved according to the situation. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna devices according to the second to fifth embodiments, the description of those similar configurations, operations, and advantages will be omitted. Seventh Embodiment A seventh embodiment of the present invention will be described. Fig. 14 is a perspective view showing an antenna device according to a seventh embodiment of the present invention. As shown in Fig. 14, the antenna device according to this embodiment is different from the antenna devices according to the first to sixth embodiments in that the first antenna unit 2 and the second antenna unit 3 are formed on a dielectric substrate 8. More specifically, the dielectric substrate 8 is a rectangular parallelepiped and includes a front face 80, side faces 81 and 82, an upper face 83, a lower face 84, and a rear face 85. The dielectric substrate 8 is provided in the non-ground region 101 of the circuit board 100. The feed electrode 4 of the first antenna unit 2 is pattern-formed on the front face 80 and the upper face 83 of the dielectric substrate 8 . A pattern 113 is formed in the non-ground region 101. One end of the feed electrode 4 is connected to the transmitter/receiver 110 through the pattern 113 and the coil 111. The other end of the feed electrode 4 is connected to the first frequency-variable circuit 6-1. Each of the first reactance circuit 6A and the second reactance circuit 6B of the first frequency-variable circuit 6-1 is a series resonant circuit. The first variable-capacitance diode 61A (the second variable-capacitance diode 61B) and the coil 62A (62B) are chip components and are connected to each other through a pattern 65 provided on the upper face 83 of the dielectric substrate 8. The first radiation electrode 5 is connected to the coil 62B of the first frequency-variable circuit 6-1. The first radiation electrode 5 extends rightward in an upper portion of the upper face 83 of the dielectric substrate 8, goes down along the side face 81, extends leftward along the lower face 84, and goes up along the side face 82. Then, the open end 50 of the first radiation electrode 5 is positioned at a corner of the upper face 83. A pattern 72 is extracted from the connection point P of the first frequency-variable circuit 6-1. The pattern 72 extends along the upper face 83 and the front face 80, and is connected to a pattern 123, which is formed in the non-ground region 101 and reaches the reception-frequency controller 120. The high-frequency cutoff resistor 121 and the DC-pass capacitor 122 are connected in the middle of the pattern 123. The second radiation electrode 7 of the second antenna unit 3 is pattern-formed on the upper face 83 of the dielectric substrate 8 and faces a direction perpendicular to the pattern 72. The second radiation electrode 7 is connected to the pattern 72 through the second frequency-variable circuit 6-2. The third reactance circuit 6C of the second frequency-variable circuit 6-2 is a series resonant circuit. The third variable-capacitance diode 61C and the coil 62C are chip components and are connected to each other through a pattern 73 provided on the upper face 83 of the dielectric substrate 8. With this configuration, the capacitance between the open end 50 of the first radiation electrode 5 and the feed electrode 4 of the first antenna unit 2 and the capacitance between the first radiation electrode 5 and the second radiation electrode 7 can be increased. Thus, by changing the dielectric constant of the dielectric substrate 8 in an appropriate manner, the reactances of the first and second antenna units 2 and 3 can be adjusted. In this embodiment, all the first antenna unit 2 and the second antenna unit 3 are formed on the dielectric substrate 8. However, at least the first antenna unit 2 can be formed on the dielectric substrate 8. Thus, the second antenna unit 3 may be formed in the non-ground region 101 of the circuit board 100. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna devices according to the first to sixth embodiments, the description of those similar configurations, operations, and advantages will be omitted. Eighth Embodiment An eighth embodiment of the present invention will be described. Fig. 15 is a schematic plan view showing an antenna device according to the eight embodiment of the present invention. Fig. 16 is a chart illustrating a variable state of multi-resonances. As shown in Fig. 15, the antenna device according to this embodiment is different from the antenna devices according to the first to seventh embodiments in that another antenna unit is added. That is, an additional radiation electrode 9, to which a ground coil 91 for adjusting a resonant frequency is connected, is connected to the connection point P through a coil 92 and is disposed in the subsequent stage of the first reactance circuit 6A. Thus, an additional antenna unit 3-1 is formed by the feed electrode 4, the first reactance circuit 6A, which is a frequency-variable circuit, and the additional radiation electrode 9. With this configuration, as shown in Fig. 16, a resonant frequency f3 of the additional antenna unit 3-1, as well as the resonant frequencies f1 and f2 of the first and second antenna units 2 and 3, can be obtained. By changing the reactances of the first and second frequency-variable circuits 6-1 and 6-2 and the first reactance circuit 6A due to the application of a control voltage Vc, the resonant frequencies f1, f2, and f3 of the first and second antenna units 2 and 3 and the additional antenna unit 3-1 can be changed at the same time by the amounts of change dl, d2, and d3 to the resonant frequencies f1', f2', and f3'. Although an example in which the additional antenna unit 3-1 including the additional radiation electrode 9 is provided has been described in this embodiment, a plurality of additional radiation electrodes 9 may be connected in parallel to each other to the connection point P so that a plurality of additional antenna units 3-1 to 3-n can be formed. Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna devices according to the first to seventh embodiments, the description of those similar configurations, operations, and advantages will be omitted. Ninth Embodiment A ninth embodiment of the present invention will be described. Fig. 17 is a schematic plan view showing an antenna device according to the ninth embodiment of the present invention. Fig. 18 is a chart illustrating a variable state of multi-resonances. As shown in Fig. 17, the antenna device according to this embodiment is different from the antenna device according to the eighth embodiment in that a reactance circuit is added to n additional antenna units 3-1 to 3-n. That is, n additional antenna units 3-1 to 3-n are provided, and an additional reactance circuit is provided in at least one of the n additional antenna units 3-1. More specifically, an additional reactance circuit 6D including a variable-capacitance diode 61D whose capacitance can be varied by a control voltage Vc is connected between the first reactance circuit 6A and an additional radiation electrode 9-1, and a frequency-variable circuit is formed by the first reactance circuit 6A and the additional reactance circuit 6D. That is, the additional antenna unit 3-1 is formed by the frequency-variable circuit, the additional radiation electrode 9-1, and the feed electrode 4. In the additional antenna unit 3-2, the coil 92 is connected to an additional radiation electrode 9-2, as in the eighth embodiment, however no additional reactance circuit is connected. Thus, the additional antenna unit 3-2 is formed by the feed electrode 4, the first reactance circuit 6A, and the additional radiation electrode 9-2. In the subsequent additional antenna units, an additional reactance circuit is provided when necessary. In the additional antenna unit 3-n, which is in the last stage, an additional reactance circuit 6E is connected to an additional radiation electrode 9-n. That is, a frequency-variable circuit is formed by the first reactance circuit 6A and the additional reactance circuit 6E. Accordingly, the additional antenna unit 3-n is formed by the feed electrode 4, the frequency-variable circuit, and the additional radiation electrode 9-n. With this configuration, as shown by a return-loss curve S1 represented by a solid line shown in Fig. 18, the resonant frequencies f1 and f2 of the first and second antenna units 2 and 3 and the resonant frequencies f3 to fn of the additional antenna units 3-1 to 3-n can be obtained. As shown by a return-loss curve S2 represented by a broken line, the resonant frequencies f1, f2, f3, f4, •••, and fn of the first and second antenna units 2 and 3 and the additional antenna units 3-1, 3-2, • • • , and 3-n are changed at the same time by the amounts of change dl, d2, d3, d4, • • • , and dn to the resonant frequencies f1', f2', f3', f4', •••, and fn'. Since the frequency-variable circuits of the additional antenna units 3-1 and 3-n have two reactance circuits (the first reactance circuit 6A and the additional reactance circuit 6D; and the first reactance circuit 6A and the additional reactance circuit 6E), the amounts of change d3 and dn from the resonant frequencies f3 and fn to the resonant frequencies f3' and fn' are greater than the amount of change d4 from the resonant frequency f4 to the resonant frequency f4' of the additional antenna unit 3-2, which includes only a single reactance circuit (the first reactance circuit 6A). Since the other configurations, operations, and advantages of the antenna device according to this embodiment are similar to those of the antenna device according to the eighth embodiment, the description of those similar configurations, operations, and advantages will be omitted. CLAIMS 1. An antenna device comprising a first antenna unit including a feed electrode connected to a feed unit, a first radiation electrode, and a first frequency-variable circuit connected between the first radiation electrode and the feed electrode; and a second antenna unit including the feed electrode, a second radiation electrode, and a second frequency-variable circuit connected between the second radiation electrode and the feed electrode, wherein the first frequency-variable circuit includes a first reactance circuit connected to the feed electrode, the first reactance circuit including a first variable-capacitance diode whose capacitance is variable using a control voltage; and a second reactance circuit connected between the first reactance circuit and the first radiation electrode, the second reactance circuit including a second variable-capacitance diode whose capacitance is variable using the control voltage, and wherein the second frequency-variable circuit includes the first reactance circuit; and a third reactance circuit connected between the first reactance circuit and the second radiation electrode, the third reactance circuit including a third variable-capacitance diode whose capacitance is variable using the control voltage. 2. The antenna device according to Claim 1, wherein the second variable-capacitance diode of the second reactance circuit and the third variable-capacitance diode of the third reactance circuit are disposed so as to associate with the first variable-capacitance diode of the first reactance circuit, cathodes of the first to third variable-capacitance diodes are connected to each other, and the control voltage is applied to a portion where the cathodes are connected to each other. 3. The antenna device according to Claim 1 or 2, wherein: the first reactance circuit is a series resonant circuit or a parallel resonant circuit including the first variable-capacitance diode; the second reactance circuit is a series resonant circuit or a parallel resonant circuit including the second variable-capacitance diode; and the third reactance circuit is a series resonant circuit or a parallel resonant circuit including the third variable-capacitance diode. 4. The antenna device according to Claim 3, wherein: each of the first to third reactance circuits is configured as a parallel resonant circuit in which a coil is connected in parallel to a series circuit including the corresponding variable-capacitance diode; and at least one of the coils of the first to third reactance circuits is set as a choke coil and the corresponding reactance circuit including the coil serves substantially as a series resonant circuit. 5. The antenna device according to any one of Claims 1 to 4, wherein an internal resistance of at least one of the first to third variable-capacitance diodes is different from internal resistances of the others of the first to third variable-capacitance diodes. 6. The antenna device according to any one of Claims 1 to 5, wherein at least the first antenna unit is formed on a dielectric substrate. 7. The antenna device according to any one of Claims 1 to 6, wherein an additional radiation electrode is connected to a stage subsequent to the first reactance circuit, which is connected to the feed electrode, and an additional antenna unit is formed by the additional radiation electrode, the feed electrode, and the first reactance circuit, which is a frequency-variable circuit. 8. The antenna device according to any one of Claims 1 to 7, wherein: a plurality of additional antenna units are provided; and in at least one of the plurality of additional antenna units, an additional reactance circuit including a variable-capacitance diode whose capacitance is variable using the control voltage is connected between the first reactance circuit and the corresponding additional radiation electrode, and a frequency-variable circuit of the at least one of the plurality of additional antenna units is formed by the additional reactance circuit and the first reactance circuit. 9. A wireless communication apparatus comprising the antenna device according to any one of Claims 1 to 8. An antenna device and a wireless communication apparatus that are capable of obtaining a plurality of resonant frequencies and varying the plurality of resonant frequencies over a wide range are provided. A first antenna unit 2 of an antenna device 1 includes a feed electrode 4, a first radiation electrode 5, and a first frequency-variable circuit 6-1. The first frequency-variable circuit 6-1 includes first and second reactance circuits 6A and 6B each including a variable-capacitance diode. A control voltage Vc is applied to the first frequency-variable circuit 6-1, and the resonant frequency of the first antenna unit 2 can thus be varied. A second antenna unit 3 includes the feed electrode 4, a second radiation electrode 7, and a second frequency-variable circuit 6-2. The second frequency-variable circuit 6-2 includes first and third reactance circuits 6A and 6C each including a variable-capacitance diode. A control voltage Vc is applied to the second frequency-variable circuit 6-2, and the resonant frequency of the second antenna unit 3 can thus be varied.

Full Text

DESCRIPTION
ANTENNA DEVICE AND WIRELESS COMMUNICATION APPARATUS
Technical Field
The present invention relates to an antenna device and a
wireless communication apparatus that are capable of varying a
resonant frequency over a certain range.
Background Art
As an antenna device of this type, for example, a
frequency-variable antenna disclosed in Patent Document 1 has
been available. The antenna device has a configuration in which
a feed electrode and a single radiation electrode are formed on
a substrate and a single frequency-variable circuit is disposed
between the feed electrode and the radiation electrode.
With this configuration, varying a control voltage to be
applied to a variable-capacitance diode contained in the
frequency-variable circuit varies a resonant frequency of the
antenna.
Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2006-060384
Disclosure of Invention
However, the above-described antenna device has the
problems described below.
Since the antenna device includes a feed electrode, a
frequency-variable circuit, and a single radiation electrode,
only a single resonant frequency can be obtained. In addition,

although the resonant frequency can be varied using the
frequency-variable circuit, since the frequency-variable
circuit, which has only a single variable-capacitance diode, is
used, the resonant frequency cannot be varied over a wide range.
In order to solve the above-mentioned problems, an object
of the present invention is to provide an antenna device and a
wireless communication apparatus that are capable of obtaining
a plurality of resonant frequencies and varying the plurality
of resonant frequencies over a wide range.
In order to solve the above-mentioned problems, according
to the invention of Claim 1, an antenna device includes a first
antenna unit including a feed electrode connected to a feed unit,
a first radiation electrode, and a first frequency-variable
circuit connected between the first radiation electrode and the
feed electrode; and a second antenna unit including the feed
electrode, a second radiation electrode, and a second
frequency-variable circuit connected between the second
radiation electrode and the feed electrode. The first
frequency-variable circuit includes a first reactance circuit
connected to the feed electrode, the first reactance circuit
including a first variable-capacitance diode whose capacitance
is variable using a control voltage; and a second reactance
circuit connected between the first reactance circuit and the
first radiation electrode, the second reactance circuit
including a second variable-capacitance diode whose capacitance

is variable using the control voltage. The second
frequency-variable circuit includes the first reactance circuit;
and a third reactance circuit connected between the first
reactance circuit and the second radiation electrode, the third
reactance circuit including a third variable-capacitance diode
whose capacitance is variable using the control voltage.
With this configuration, when electric power is supplied
from the feed unit to the feed electrode, the first antenna unit
resonates with electric power at a frequency and transmits an
electric wave at the frequency. In addition, the second antenna
unit resonates with electric power at a frequency that is
different from the resonant frequency of the first antenna unit
and transmits an electric wave at the different frequency. That
is, the antenna device according to the present invention is
capable of achieving a two-resonant state exhibiting a resonant
frequency of the first antenna unit and a resonant frequency of
the second antenna unit. In addition, since the capacitance of
the second variable-capacitance diode of the second reactance
circuit, as well as the capacitance of the first
variable-capacitance diode of the first reactance circuit, can
be varied using a control voltage, a large reactance change for
two variable-capacitance diodes can be achieved by the first
frequency-variable circuit. As a result, the resonant frequency
of the first antenna unit can be varied over a wide range. In
addition, since the capacitance of the first

variable-capacitance diode of the first reactance circuit and
the capacitance of the third variable-capacitance diode of the
third reactance circuit are controlled using the control voltage,
a large reactance change for two variable-capacitance diodes can
be achieved by the second frequency-variable circuit. As a
result, the resonant frequency of the second antenna unit can
also be varied over a wide range.
According to the invention of Claim 2, in the antenna device
according to Claim 1, the second variable-capacitance diode of
the second reactance circuit and the third variable-capacitance
diode of the third reactance circuit may be disposed so as to
associate with the first variable-capacitance diode of the first
reactance circuit, cathodes of the first to third
variable-capacitance diodes may be connected to each other, and
the control voltage may be applied to a portion where the cathodes
are connected to each other.
With this configuration, the three variable-capacitance
diodes of the first to third variable-capacitance diodes can be
varied at the same time using the control voltage.
According to the invention of Claim 3, in the antenna device
according to Claim 1 or 2, the first reactance circuit may be
a series resonant circuit or a parallel resonant circuit
including the first variable-capacitance diode, the second
reactance circuit may be a series resonant circuit or a parallel
resonant circuit including the second variable-capacitance diode,

and the third reactance circuit may be a series resonant circuit
or a parallel resonant circuit including the third
variable-capacitance diode.
With this configuration, when all the first to third
reactance circuits are configured as series resonant circuits,
a large gain can be obtained without greatly increasing variable
ranges of the resonant frequency of the first antenna unit and
the resonant frequency of the second antenna unit. When all the
first to third reactance circuits are configured as parallel
resonant circuits, variable ranges of the resonant frequency of
the first antenna unit and the resonant frequency of the second
antenna unit can be increased although a large gain is not obtained
Thus, when at least one of the first to third reactance circuits
is configured as a series resonant circuit and the others of the
first to third reactance circuits are configured as parallel
resonant circuits, the amount of change in the resonant frequency
of the first antenna unit can be made different from the amount
of change in the resonant frequency of the second antenna unit.
According to the invention of Claim 4, in the antenna device
according to Claim 3, each of the first to third reactance circuits
may be configured as a parallel resonant circuit in which a coil
is connected in parallel to a series circuit including the
corresponding variable-capacitance diode, and at least one of
the coils of the first to third reactance circuits may be set
as a choke coil and the corresponding reactance circuit including

the coil may serve substantially as a series resonant circuit.
With this configuration, when the coil of the parallel
resonant circuit is used as a choke coil, a reactance circuit
including the coil is substantially capable of serving as a series
resonant circuit. Thus, design can be easily changed without
requiring reconfiguration of a parallel resonant circuit portion
into a series resonant circuit.
According to the invention of Claim 5, in the antenna device
according to any one of Claims 1 to 4, an internal resistance
of at least one of the first to third variable-capacitance diodes
may be different from internal resistances of the others of the
first to third variable-capacitance diodes. When the internal
resistance of a variable-capacitance diode is reduced, although
a gain is increased, a variable-capacitance range becomes
narrower. In contrast, when the internal resistance is increased,
although a gain is reduced, a variable capacitance range becomes
wider. Thus, with this configuration, when the internal
resistance of at least one of the first to third
variable-capacitance diodes is made different from the internal
resistances of the others of the first to third
variable-capacitance diodes while considering which of a
frequency variable range or a gain is to be emphasized,
characteristics of the first antenna unit and the second antenna
unit can be obtained according to the situation.
According to the invention of Claim 6, in the antenna device

according to any one of Claims 1 to 5, at least the first antenna
unit may be formed on a dielectric substrate.
With this configuration, the capacitance of at least the
first antenna unit can be increased, and the reactance of the
first antenna unit can be increased.
According to the invention of Claim 7, in the antenna device
according to any one of Claims 1 to 6, an additional radiation
electrode may be connected to a stage subsequent to the first
reactance circuit, which is connected to the feed electrode, and
an additional antenna unit may be formed by the additional
radiation electrode, the feed electrode, and the first reactance
circuit, which is a frequency-variable circuit.
With this configuration, the resonant frequency of the
additional antenna unit, as well as the resonant frequencies of
the first and second antenna units, can be obtained. Thus,
electric waves of more resonant frequencies can be handled. In
addition, the resonant frequencies of the first and second
antenna unit and the resonant frequency of the additional antenna
unit can be varied at the same time.
According to the invention of Claim 8, in the antenna device
according to any one of Claims 1 to 7, a plurality of additional
antenna units may be provided, and in at least one of the plurality
of additional antenna units, an additional reactance circuit
including a variable-capacitance diode whose capacitance is
variable using the control voltage may be connected between the

first reactance circuit and the corresponding additional
radiation electrode, and a frequency-variable circuit of the at
least one of the plurality of additional antenna units may be
formed by the additional reactance circuit and the first
reactance circuit.
With this configuration, since the frequency-variable
circuit of the additional antenna unit is formed by the additional
reactance circuit and the first reactance circuit, the resonant
frequency of the additional antenna unit can be varied over a
wide range.
A wireless communication apparatus according to Claim 9
includes the antenna device according to any one of Claims 1 to
8.
As described above, since the antenna device according to
the present invention includes a plurality of antenna units, an
excellent advantage of obtaining a plurality of resonant
frequencies can be achieved. Moreover, since a
frequency-variable circuit of each of the plurality of antenna
units includes two reactance circuits each including a
variable-capacitance diode, a large reactance change for two
variable-capacitance diodes can be achieved. As a result, the
resonant frequency of each of the plurality of antenna units can
be varied over a wider range.
In addition, in the antenna device according to the
invention of Claim 3, a large gain can be obtained when all the

first to third reactance circuits are configured as series
resonant circuit, and a wide variable range of a resonant
frequency can be achieved when all the first to third reactance
circuits are configured as parallel resonant circuits . When both
a series resonant circuit and a parallel resonant circuit are
used, the amount of change in the resonant frequency and the gain
of the first antenna unit can be made different from the amount
of change in the resonant frequency and the gain of the second
antenna unit. As a result, optimal characteristics can be
achieved according to the use state.
In addition, in the antenna device according to the
invention of Claim 4, there is no need to reconfigure a parallel
resonant circuit portion into a series resonant circuit. Thus,
a design change from a parallel resonant circuit into a series
resonant circuit can be performed easily.
In addition, in the antenna device according to the
invention of Claim 5, characteristics of the first antenna unit
and the second antenna unit can be obtained according to the
situation.
In addition, in the antenna device according to claim 6,
the reactance of at least the first antenna unit can be increased.
Thus, the resonant frequency of the first antenna unit can be
reduced.
In addition, in the antenna device according to the
invention of Claim 7, a larger number of resonances can be obtained

Moreover, the resonant frequencies can be varied at the same time.
In particular, according to the invention of Claim 8, the
resonant frequencies of the additional antenna units can be
varied over a wide range.
In addition, in the wireless communication apparatus
according to the invention of Claim 9, transmission and reception
can be performed such that a frequency change can be achieved
over a wide range for multi-resonances.
Brief Description of the Drawings
Fig. 1 is a schematic plan view showing an antenna device
according to a first embodiment of the present invention.
Fig. 2 is a chart illustrating a variable state of two
resonances.
Fig. 3 is a schematic plan view showing an antenna device
according to a second embodiment of the present invention.
Fig. 4 is a chart illustrating a variable state of two
resonances.
Fig. 5 is a schematic plan view showing an antenna device
according to a third embodiment of the present invention.
Fig. 6 is a chart illustrating a variable state of two
resonances.
Fig. 7 is a schematic plan view showing an antenna device
according to a fourth embodiment of the present invention.
Fig. 8 is a chart illustrating a variable state of two
resonances.

Fig. 9 is a schematic plan view showing an antenna device
according to a fifth embodiment of the present invention.
Fig. 10 is a chart illustrating a variable state of two
resonances.
Fig. 11 is a schematic plan view showing an antenna device
according to a sixth embodiment of the present invention.
Fig. 12 is a chart illustrating the relationship between
a frequency and a gain when a variable-capacitance diode has a
large internal resistance.
Fig. 13 is a chart illustrating the relationship between
a frequency and a gain when a variable-capacitance diode has a
small internal resistance.
Fig. 14 is a perspective view showing an antenna device
according to a seventh embodiment of the present invention.
Fig. 15 is a schematic plan view showing an antenna device
according to an eighth embodiment of the present invention.
Fig. 16 is a chart illustrating a variable state of
multi-resonances.
Fig. 17 is a schematic plan view showing an antenna device
according to a ninth embodiment of the present invention.
Fig. 18 is a chart illustrating a variable state of
multi-resonances.
Reference Numerals
1: antenna device, 2: first antenna unit, 3: second antenna
unit, 3-1 to 3-n: additional antenna unit, 4: feed electrode,

5: first radiation electrode, 6-1: first frequency-variable
circuit, 6-2: second frequency-variable circuit, 6A: first
reactance circuit, 6B: second reactance circuit, 6C: third
reactance circuit, 6D and 6E: additional reactance circuit, 7:
second radiation electrode, 8: dielectric substrate, 9 and 9-1
to 9-n: additional radiation electrode, 50: open end, 51, 71,
and 91: ground coil, 61A: first variable-capacitance diode, 61B:
second variable-capacitance diode, 61C: third
variable-capacitance diode, 61D and 61E: variable-capacitance
diode, 62A, 62B, 62C, 63A, 63B, and 63C: coil, 64: common capacitor,
100: circuit board, 101: non-ground region, 102: ground region,
110: transmitter/receiver, 120: reception-frequency controller,
G: gap, P: connection point, S1: return-loss curve, S2:
return-loss curve, Vc: control voltage, dl, d2, d3, d4, • • • and
dn: amount of change, f1, f2, f3, f4, ••• and fn: resonant
frequency
Best Mode for Carrying Out the Invention
The best mode for carrying out the present invention will
be described with reference to the drawings.
First Embodiment
Fig. 1 is a schematic plan view showing an antenna device
according to a first embodiment of the present invention.
An antenna device 1 according to this embodiment is provided
in a wireless communication apparatus, such as a cellular phone.
As shown in Fig. 1, the antenna device 1 is formed in a

non-ground region 101 of a circuit board 100 of the wireless
communication apparatus. The antenna device 1 transfers
high-frequency signals to and from a transmitter/receiver 110,
which is provided in a ground region 102 and serves as a power-feed
unit. A reception-frequency controller 120 provided in the
transmitter/receiver 110 applies a direct-current control
voltage Vc to the antenna device 1.
The antenna device 1 includes a first antenna unit 2 and
a second antenna unit 3.
The first antenna unit 2 includes a feed electrode 4, a
first radiation electrode 5, and a first frequency-variable
circuit 6-1 connected between the feed electrode 4 and the first
radiation electrode 5.
More specifically, a matching circuit including coils 111
and 112 is formed in the non-ground region 101, and the feed
electrode 4, which is a conductive pattern, is connected to the
transmitter/receiver 110 through the matching circuit.
The first radiation electrode 5 is a conductive pattern
having a loop shape. An open end 50 of the first radiation
electrode 5 faces the feed electrode 4 with a gap G therebetween.
The gap G causes a capacitance between the feed electrode 4 and
the first radiation electrode 5. By varying the size of the gap
G, the reactance of the first antenna unit 2 can be set to a desired
value. A ground coil 51, which is provided for resonant frequency
adjusting, is connected in the middle of the first radiation

electrode 5.
The first frequency-variable circuit 6-1 includes a first
reactance circuit 6A (represented by "jX1" in Fig. 1) , which is
connected to the feed electrode 4, and a second reactance circuit
6B (represented by "jX2" in Fig. 1), which is connected between
the first reactance circuit 6A and the first radiation electrode
5. The first reactance circuit 6A includes a first
variable-capacitance diode, which is not shown. When a control
voltage Vc is applied to the first variable-capacitance diode,
the capacitance of the first variable-capacitance diode
increases or decreases, resulting in a change in the reactance
of the first reactance circuit 6A.
The second reactance circuit 6B includes a second
variable-capacitance diode, which is not shown. When a control
voltage Vc is applied to the second variable-capacitance diode,
the capacitance of the second variable-capacitance diode
increases or decreases, resulting in a change in the reactance
of the second reactance circuit 6B.
A connection point P between the first reactance circuit
6A and the second reactance circuit 6B is connected to the
reception-frequency controller 120 through a high-frequency
cutoff resistor 121 and a DC-pass capacitor 122.
With this configuration, when the reception-frequency
controller 120 applies a control voltage Vc to the connection
point P, the reactances of the first and second reactance circuits

6A and 6B increase or decrease in accordance with the size of
the control voltage Vc, resulting in a change in the reactance
of the entire first frequency-variable circuit 6-1, as described
above. That is, applying the control voltage Vc to the first
frequency-variable circuit 6-1 varies the electrical length of
the first antenna unit 2, thus varying the resonant frequency
of the first antenna unit 2.
The second antenna unit 3 includes the feed electrode 4,
a second radiation electrode 7, and a second frequency-variable
circuit 6-2 connected between the feed electrode 4 and the second
radiation electrode 7.
More specifically, the second radiation electrode 7 is a
conductive pattern having a line shape. A ground coil 71, which
is provided for resonant frequency adjusting, is connected to
an end of the second radiation electrode 7.
The second frequency-variable circuit 6-2 includes the
first reactance circuit 6A and a third reactance circuit 6C
(represented by "jX3" in Fig. 1) , which is connected between the
first reactance circuit 6A and the second radiation electrode
7.
Similarly to the first reactance circuit 6A, the third
reactance circuit 6C includes a third variable-capacitance diode,
which is not shown. When a control voltage Vc is applied to the
third variable-capacitance diode, the capacitance of the third
variable-capacitance diode increases or decreases, resulting in

a change in the reactance of the third reactance circuit 6C.
The third reactance circuit 6C is also connected to the
connection point P between the first reactance circuit 6A and
the second reactance circuit 6B. When the reception-frequency
controller 120 applies a control voltage Vc to the connection
point P, the reactances of the first and third reactance circuits
6A and 6C increase or decrease in accordance with the size of
the control voltage Vc, resulting in a change in the reactance
of the entire second frequency-variable circuit 6-2. That is,
applying the control voltage Vc to the second frequency-variable
circuit 6-2 varies the electrical length of the second antenna
unit 3, thus varying the resonant frequency of the second antenna
unit 3.
Operations and advantages of the antenna device according
to this embodiment will be described.
Fig. 2 is a chart illustrating a variable state of two
resonances.
As described above, the first antenna unit 2 includes the
feed electrode 4, the first frequency-variable circuit 6-1, and
the first radiation electrode 5, and the second antenna unit 3
includes the feed electrode 4, the second frequency-variable
circuit 6-2, and the second radiation electrode 7. With this
configuration, a two-resonant state exhibiting a resonant
frequency f 1 of the first antenna unit 2 and a resonant frequency
f2 of the second antenna unit 3 can be achieved.

For example, when the length of the first radiation
electrode 5 is set to be longer than the length of the second
radiation electrode 7, the resonant frequency f1 of the first
antenna unit 2 is lower than the resonant frequency f2 of the
second antenna unit 3. In this case, a return-loss curve S1
represented by a solid line shown in Fig. 2 is obtained.
When a control voltage Vc is applied to the first
frequency-variable circuit 6-1, the reactances of the first and
second reactance circuits 6A and 6B increase or decrease in
accordance with the size of the control voltage Vc, resulting
in a change in the reactance of the entire first
frequency-variable circuit 6-1. Thus, the electrical length of
the first antenna unit 2 is changed, and the resonant frequency
fl of the first antenna unit 2 is changed.
In parallel to this, the reactances of the first and third
reactance circuits 6A and 6C of the second frequency-variable
circuit 6-2 also increase or decrease in accordance with the size
of the control voltage Vc, resulting in a change in the reactance
of the entire second frequency-variable circuit 6-2. Thus, the
electrical length of the second antenna unit 3 is changed, and
the resonant frequency f2 of the second antenna unit 3 is changed.
As a result, as shown by a return-loss curve S2 represented
by a broken line shown in Fig. 2, the resonant frequency fl of
the first antenna unit 2 moves by the amount of change d1, which
corresponds to the size of the control voltage Vc, and reaches

a frequency f1'. At the same time, the resonant frequency f2
of the second antenna unit 3 moves by the amount of change d2,
which corresponds to the size of the control voltage Vc, and
reaches a frequency f2'.
At this time, the amount of change d1 (d2), by which the
resonant frequency f1 (f2) is changed to the resonant frequency
f1' (f2') by the first frequency-variable circuit 6-1 (the second
frequency-variable circuit 6-2), is obtained not only from the
amount of change in the capacitance of the first
variable-capacitance diode included in the first reactance
circuit 6A but also from the amount of change in the capacitance
of the second variable-capacitance diode (the third
variable-capacitance diode) included in the second reactance
circuit 6B (the third reactance circuit 6C). Thus, the large
amount of change dl (d2) can be obtained. As a result, the
resonant frequency fl (f2) of the first antenna unit 2 (the second
antenna unit 3) can be varied over a wide range.
In the antenna device of the related art, only a single
resonance appears and a resonant frequency is varied by a
frequency-variable circuit including only a single
variable-capacitance diode. Thus, in order to vary the resonant
frequency over a wide range from fl to f2', as shown in Fig. 2,
a large control voltage Vc is necessary. Such an antenna device
is not suitable for a wireless communication apparatus, such as
a cellular phone, which requires a lower voltage specification.

In contrast, in the antenna device 1 according to this
embodiment, the resonant frequencies f1 and f2 in the
two-resonant state can be varied at the same time by a
predetermined control voltage Vc, as described above. Thus, a
resonant frequency can be varied over a wide range from fl to
f2' by the application of a low control voltage Vc. Thus, the
antenna device 1 according to this embodiment is suitable for
a wireless communication apparatus, such as a cellular phone,
which requires a lower power-supply voltage.
Second Embodiment
A second embodiment of the present invention will be
described.
Fig. 3 is a schematic plan view showing an antenna device
according to the second embodiment of the present invention.
The antenna device according to this embodiment is provided
in which a concrete series resonant circuit is applied to each
of the first reactance circuit 6A, the second reactance circuit
6B, and the third reactance circuit 6C used in the first
embodiment.
As shown in Fig. 3, the first reactance circuit 6A, the
second reactance circuit 6B, and the third reactance circuit 6C
are configured as a series resonant circuit including a first
variable-capacitance diode 61A, a series resonant circuit
including a second variable-capacitance diode 61B, and a series
resonant circuit including a third variable-capacitance diode

61C, respectively.
More specifically, a series resonant circuit including the
first variable-capacitance diode 61A and a coil 62A is used as
the first reactance circuit 6A. The coil 62A is connected to
the feed electrode 4. The cathode of the first
variable-capacitance diode 61A is connected to the connection
point P. A series resonant circuit including the second
variable-capacitance diode 61B and a coil 62B is used as the second
reactance circuit 6B. The coil 62B is connected to the first
radiation electrode 5. The cathode of the second
variable-capacitance diode 61B is connected to the connection
point P. A series resonant circuit including the third
variable-capacitance diode 61C and a coil 62C is used as the third
reactance circuit 6C. The coil 62C is connected to the second
radiation electrode 7. The cathode of the third
variable-capacitance diode 61C is connected to the connection
point P.
That is, the second variable-capacitance diode 61B of the
second reactance circuit 6B and the third variable-capacitance
diode 61C of the third reactance circuit 6C are disposed so as
to associate with the first variable-capacitance diode 61A of
the first reactance circuit 6A. The cathodes of the first to
third variable-capacitance diodes 61A to 61C are connected to
each other. A control voltage Vc is applied to a portion where
the cathodes are connected to each other.

Operations and advantages of the antenna device according
to this embodiment will be described.
Fig. 4 is a chart illustrating a variable state of two
resonances.
As shown by a return-loss curve S1 represented by a solid
line shown in Fig. 4, in the antenna device according to this
embodiment, a two-resonant state exhibiting a resonant frequency
f1 of the first antenna unit 2 and a resonant frequency f2 of
the second antenna unit 3 can be achieved. Applying a control
voltage Vc to each of the first frequency-variable circuit 6-1
and the second frequency-variable circuit 6-2 varies the resonant
frequency f 1 of the first antenna unit 2 and the resonant frequency
f2 of the second antenna unit 3 at the same time.
In the series resonant circuit including the first
variable-capacitance diode and the coil, the reactance with
respect to the control voltage Vc varies substantially linearly.
Thus, although the amount of change dl (d2) from the resonant
frequency f1 to the resonant frequency f1' (f2 to f2') by the
first frequency-variable circuit 6-1 (the second
frequency-variable circuit 6-2) is not very large, a large gain
can be achieved. Consequently, in a case where all the first
to third reactance circuits 6A to 6C are configured as series
resonant circuits as in this embodiment, an antenna device in
which a gain is emphasized can be achieved.
Since the other configurations, operations, and advantages

of the antenna device according to this embodiment are similar
to those of the antenna device according to the first embodiment,
the description of those similar configurations, operations, and
advantages will be omitted.
Third Embodiment
A third embodiment of the present invention will be
described.
Fig. 5 is a schematic plan view showing an antenna device
according to the third embodiment of the present invention.
The antenna device according to this embodiment is provided
in which a concrete parallel resonant circuit is applied to each
of the first reactance circuit 6A, the second reactance circuit
6B, and the third reactance circuit 6C used in the first
embodiment.
That is, as shown in Fig. 5, the first reactance circuit
6A, the second reactance circuit 6B, and the third reactance
circuit 6C are configured as a parallel resonant circuit
including the first variable-capacitance diode 61A, a parallel
resonant circuit including the second variable-capacitance diode
61B, and a parallel resonant circuit including the third
variable-capacitance diode 61C, respectively.
More specifically, a parallel resonant circuit in which
a series circuit including a coil 63A and a common capacitor 64
is connected in parallel to the series circuit including the first
variable-capacitance diode 61A and the coil 62A is used as the

first reactance circuit 6A. A parallel resonant circuit in which
a series circuit including a coil 63B and the common capacitor
64 is connected in parallel to the series circuit including the
second variable-capacitance diode 61B and the coil 62B is used
as the second reactance circuit 6B. A parallel resonant circuit
in which a coil 63C is connected in parallel to the series circuit
including the third variable-capacitance diode 61C and the coil
62C is used as the third reactance circuit 6C.
Operations and advantages of the antenna device according
to this embodiment will be described.
Fig. 6 is a chart illustrating a variable state of two
resonances.
As shown by a return-loss curve S1 represented by a solid
line shown in Fig. 6, the antenna device according to this
embodiment achieves a two-resonant state exhibiting a resonant
frequency f 1 of the first antenna unit 2 and a resonant frequency
f2 of the second antenna unit 3, as in the first embodiment.
Applying a control voltage Vc to each of the first
frequency-variable circuit 6-1 and the second frequency-variable
circuit 6-2 varies the resonant frequency f 1 of the first antenna
unit 2 and the resonant frequency f2 of the second antenna unit
3 at the same time.
In the parallel resonant circuit in which a series circuit
including a variable-capacitance diode and a coil is connected
in parallel to another coil, the reactance with respect to the

control voltage varies nonlinearly. Thus, although a large gain
is not obtained, a significantly large amount of change d1 (d2)
from the resonant frequency f1 to the resonant frequency f1' (f2
to f2') by the first frequency-variable circuit 6-1 (the second
frequency-variable circuit 6-2) can be achieved. Consequently,
in a case where all the first to third reactance circuits 6A to
6C are configured as parallel resonant circuits as in this
embodiment, an antenna device that is capable of varying a
frequency over a wide range can be achieved.
Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna devices according to the first and second
embodiments, the description of those similar configurations,
operations, and advantages will be omitted.
Fourth Embodiment
A fourth embodiment of the present invention will be
described.
Fig. 7 is a schematic plan view showing an antenna device
according to the fourth embodiment of the present invention.
The antenna device according to this embodiment is provided
in which both a series resonant circuit and a parallel resonant
circuit are applied to the first reactance circuit 6A, the second
reactance circuit 6B, and the third reactance circuit 6C used
in the first embodiment.
That is, as shown in Fig. 7, the first reactance circuit

6A and the second reactance circuit 6B are configured as a parallel
resonant circuit including the first variable-capacitance diode
61A and a parallel resonant circuit including the second
variable-capacitance diode 61B, respectively. The third
reactance circuit 6C is configured as a series resonant circuit
including the third variable-capacitance diode 61C.
Operations and advantages of the antenna device according
to this embodiment will be described.
Fig. 8 is a chart illustrating a variable state of two
resonances.
As shown by a return-loss curve S1 represented by a solid
line shown in Fig. 8, the antenna device according to this
embodiment also achieves two resonances f 1 and f2 caused by the
first and second antenna units 2 and 3. Applying a control
voltage Vc to each of the first and second frequency-variable
circuits 6-1 and 6-2 varies the resonant frequency f 1 of the first
antenna unit 2 and the resonant frequency f2 of the second antenna
unit 3 at the same time.
In the first frequency-variable circuit 6-1 including the
first reactance circuit 6A and the second reactance circuit 6B,
which are configured as parallel resonant circuits, the reactance
with respect to the control voltage Vc varies nonlinearly, as
described above. Thus, although a large gain is not achieved,
the amount of change d1 from the resonant frequency f1 to the
resonant frequency f1' is significantly large, as shown in Fig.

8. In the third reactance circuit 6C, which is a series resonant
circuit, the reactance with respect to the control voltage Vc
varies linearly. Thus, although a large amount of change in the
reactance is not achieved, a large gain can be obtained. As a
result, the amount of change d2 from the resonant frequency f2
to the resonant frequency f2' by the second frequency-variable
circuit 6-2, which includes the first reactance circuit 6A
configured as a parallel resonant circuit and the third reactance
circuit 6C configured as a series resonant circuit, is small.
That is, according to this embodiment, an antenna device
that is capable of achieving a large amount of change d1 of the
resonant frequency f1 and ensuring a certain amount of change
d2 of the resonant frequency f2 while obtaining a large gain can
be achieved.
The antenna device including the first reactance circuit
6A and the second reactance circuit 6B, which are configured as
parallel resonant circuits, and the third reactance circuit 6C,
which is configured as a series resonant circuit, has been
explained in this embodiment. However, the present invention
is not limited to this. Determination of which reactance circuit
is to be configured as a parallel resonant circuit and
determination of which reactance circuit is to be configured as
a series resonant circuit can be performed in accordance with
which of the variation width of a resonant frequency band or the
gain is to be emphasized.

Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna devices according to the second and third
embodiments, the description of those similar configurations,
operations, and advantages will be omitted.
Fifth Embodiment
A fifth embodiment of the present invention will be
described.
Fig. 9 is a schematic plan view showing an antenna device
according to the fifth embodiment of the present invention. Fig.
10 is a chart illustrating a variable state of two resonances.
The antenna device according to this embodiment has a
configuration in which both a series resonant circuit and a
parallel resonant circuit are applied to the first reactance
circuit 6A, the second reactance circuit 6B, and the third
reactance circuit 6C, as in the fourth embodiment. However, the
antenna device according to this embodiment is different from
the antenna device according to the fourth embodiment in that
a series resonant circuit is formed using a choke coil.
That is, as shown in Fig. 9, the first reactance circuit
6A, the second reactance circuit 6B, and the third reactance
circuit 6C are configured as parallel circuits. By using a choke
coil as a coil of the second reactance circuit 6B, the second
reactance circuit 6B is substantially capable of serving as a
series resonant circuit.

More specifically, the second reactance circuit 6B is
formed by connecting a series circuit including the common
capacitor 64 and a coil 63B' in parallel to the series circuit
including the second variable-capacitance diode 61B and the coil
62B. The coil 63B' is set as a choke coil for cutting off electric
power having an in-band frequency of the first antenna unit 2.
The coil 63B' can be set as a choke coil by adjusting the inductance
of the coil 63B'. That is, the second reactance circuit 6B is
substantially configured so as to function as a series resonant
circuit including the first variable-capacitance diode 61A and
the coil 62B.
With this configuration, as shown by a return-loss curve
S1 represented by a solid line and a return-loss curve S2
represented by a broken line shown in Fig. 10, the first
frequency-variable circuit 6-1 achieves a large gain while
ensuring a certain amount of change d1 of the resonant frequency
f 1 and the second frequency-variable circuit 6-2 achieves a large
amount of change d2 of the resonant frequency f2.
As described above, according to this embodiment, all the
first to third reactance circuits 6A to 6C are designed as parallel
circuits, and one of the coils 63A to 63C is set as a choke coil
by adjusting the inductance of the one of the coils 63A to 63C
according to the situation. Thus, a parallel circuit including
the choke coil functions substantially as a series resonant
circuit. Consequently, design can be changed easily without

requiring reconfiguration of a parallel circuit portion into a
serial resonant circuit.
Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna device according to the fourth embodiment,
the description of those similar configurations, operations, and
advantages will be omitted.
Sixth Embodiment
A sixth embodiment of the present invention will be
described.
Fig. 11 is a schematic plan view showing an antenna device
according to the sixth embodiment of the present invention.
In the antenna device according to this embodiment, all
the first reactance circuit 6A, the second reactance circuit 6B,
and the third reactance circuit 6C are configured as parallel
resonant circuits, as in the third embodiment. However, the
antenna device according to this embodiment is different from
the antenna devices according to the third to fifth embodiments
in that functions similar to functions attained in a case where
a series resonant circuit and a parallel resonant circuit are
applied to the first to third reactance circuits 6A to 6C can
be attained by using an internal resistance of a
variable-capacitance diode.
Fig. 12 is a chart illustrating the relationship between
the frequency and the gain when a variable-capacitance diode has

a large internal resistance. Fig. 13 is a chart illustrating
the relationship between the frequency and the gain when a
variable-capacitance diode has a small internal resistance.
Each variable-capacitance diode has an internal resistance
that is characteristic of the diode. As shown in Fig. 12, the
larger the internal resistance of a variable-capacitance diode
is, the smaller the gain is. However, when such a
variable-capacitance diode is used, a variable-capacitance range
is increased. In contrast, the smaller the internal resistance
is, the larger the gain is, as shown in Fig. 13. However, when
such a variable-capacitance diode is used, a variable capacitance
range is reduced.
The antenna device according to this embodiment utilizes
such characteristics of variable-capacitance diodes. The
internal resistances Ra, Rb, and Re of the first
variable-capacitance diode 61A, the second variable-capacitance
diode 61B, and the third variable-capacitance diode 61C are set
to Ra > Rb > Re.
With this configuration, the first frequency-variable
circuit 6-1 is capable of varying the resonant frequency f1 of
the first antenna unit 2 over a wide range and the second
frequency-variable circuit 6-2 is capable of varying the resonant
frequency f2 over a predetermined range and obtaining a large
gain.
In this embodiment, the internal resistances Ra, Rb, and

Re of the first variable-capacitance diode 61A, the second
variable-capacitance diode 61B, and the third
variable-capacitance diode 61C are set to Ra > Rb > Re. The values
of the internal resistances can be determined depending on which
of a frequency variable range or a gain is to be emphasized.
Thus, when all the internal resistances Ra to Re are set
to the same large value, the first and second frequency-variable
circuits 6-1 and 6-2 are capable of achieving a wide variable
range for the resonant frequencies f1 and f2. When all the
internal resistances Ra to Re are set to the same small value,
a large gain can be achieved in each of the first antenna unit
2 and the second antenna unit 3. In addition, when at least one
of the internal resistances Ra to Re is set to be different from
the others of the internal resistances Ra to Re in an appropriate
manner, optimal characteristics of the first and second antenna
units 2 and 3 can be achieved according to the situation.
Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna devices according to the second to fifth
embodiments, the description of those similar configurations,
operations, and advantages will be omitted.
Seventh Embodiment
A seventh embodiment of the present invention will be
described.
Fig. 14 is a perspective view showing an antenna device

according to a seventh embodiment of the present invention.
As shown in Fig. 14, the antenna device according to this
embodiment is different from the antenna devices according to
the first to sixth embodiments in that the first antenna unit
2 and the second antenna unit 3 are formed on a dielectric
substrate 8.
More specifically, the dielectric substrate 8 is a
rectangular parallelepiped and includes a front face 80, side
faces 81 and 82, an upper face 83, a lower face 84, and a rear
face 85. The dielectric substrate 8 is provided in the non-ground
region 101 of the circuit board 100.
The feed electrode 4 of the first antenna unit 2 is
pattern-formed on the front face 80 and the upper face 83 of the
dielectric substrate 8 . A pattern 113 is formed in the non-ground
region 101. One end of the feed electrode 4 is connected to the
transmitter/receiver 110 through the pattern 113 and the coil
111. The other end of the feed electrode 4 is connected to the
first frequency-variable circuit 6-1. Each of the first
reactance circuit 6A and the second reactance circuit 6B of the
first frequency-variable circuit 6-1 is a series resonant circuit.
The first variable-capacitance diode 61A (the second
variable-capacitance diode 61B) and the coil 62A (62B) are chip
components and are connected to each other through a pattern 65
provided on the upper face 83 of the dielectric substrate 8.
The first radiation electrode 5 is connected to the coil

62B of the first frequency-variable circuit 6-1. The first
radiation electrode 5 extends rightward in an upper portion of
the upper face 83 of the dielectric substrate 8, goes down along
the side face 81, extends leftward along the lower face 84, and
goes up along the side face 82. Then, the open end 50 of the
first radiation electrode 5 is positioned at a corner of the upper
face 83.
A pattern 72 is extracted from the connection point P of
the first frequency-variable circuit 6-1. The pattern 72 extends
along the upper face 83 and the front face 80, and is connected
to a pattern 123, which is formed in the non-ground region 101
and reaches the reception-frequency controller 120. The
high-frequency cutoff resistor 121 and the DC-pass capacitor 122
are connected in the middle of the pattern 123.
The second radiation electrode 7 of the second antenna unit
3 is pattern-formed on the upper face 83 of the dielectric
substrate 8 and faces a direction perpendicular to the pattern
72. The second radiation electrode 7 is connected to the pattern
72 through the second frequency-variable circuit 6-2.
The third reactance circuit 6C of the second
frequency-variable circuit 6-2 is a series resonant circuit. The
third variable-capacitance diode 61C and the coil 62C are chip
components and are connected to each other through a pattern 73
provided on the upper face 83 of the dielectric substrate 8.
With this configuration, the capacitance between the open

end 50 of the first radiation electrode 5 and the feed electrode
4 of the first antenna unit 2 and the capacitance between the
first radiation electrode 5 and the second radiation electrode
7 can be increased. Thus, by changing the dielectric constant
of the dielectric substrate 8 in an appropriate manner, the
reactances of the first and second antenna units 2 and 3 can be
adjusted.
In this embodiment, all the first antenna unit 2 and the
second antenna unit 3 are formed on the dielectric substrate 8.
However, at least the first antenna unit 2 can be formed on the
dielectric substrate 8. Thus, the second antenna unit 3 may be
formed in the non-ground region 101 of the circuit board 100.
Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna devices according to the first to sixth
embodiments, the description of those similar configurations,
operations, and advantages will be omitted.
Eighth Embodiment
An eighth embodiment of the present invention will be
described.
Fig. 15 is a schematic plan view showing an antenna device
according to the eight embodiment of the present invention. Fig.
16 is a chart illustrating a variable state of multi-resonances.
As shown in Fig. 15, the antenna device according to this
embodiment is different from the antenna devices according to

the first to seventh embodiments in that another antenna unit
is added.
That is, an additional radiation electrode 9, to which a
ground coil 91 for adjusting a resonant frequency is connected,
is connected to the connection point P through a coil 92 and is
disposed in the subsequent stage of the first reactance circuit
6A.
Thus, an additional antenna unit 3-1 is formed by the feed
electrode 4, the first reactance circuit 6A, which is a
frequency-variable circuit, and the additional radiation
electrode 9.
With this configuration, as shown in Fig. 16, a resonant
frequency f3 of the additional antenna unit 3-1, as well as the
resonant frequencies f1 and f2 of the first and second antenna
units 2 and 3, can be obtained.
By changing the reactances of the first and second
frequency-variable circuits 6-1 and 6-2 and the first reactance
circuit 6A due to the application of a control voltage Vc, the
resonant frequencies f1, f2, and f3 of the first and second antenna
units 2 and 3 and the additional antenna unit 3-1 can be changed
at the same time by the amounts of change dl, d2, and d3 to the
resonant frequencies f1', f2', and f3'.
Although an example in which the additional antenna unit
3-1 including the additional radiation electrode 9 is provided
has been described in this embodiment, a plurality of additional

radiation electrodes 9 may be connected in parallel to each other
to the connection point P so that a plurality of additional antenna
units 3-1 to 3-n can be formed.
Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna devices according to the first to seventh
embodiments, the description of those similar configurations,
operations, and advantages will be omitted.
Ninth Embodiment
A ninth embodiment of the present invention will be
described.
Fig. 17 is a schematic plan view showing an antenna device
according to the ninth embodiment of the present invention. Fig.
18 is a chart illustrating a variable state of multi-resonances.
As shown in Fig. 17, the antenna device according to this
embodiment is different from the antenna device according to the
eighth embodiment in that a reactance circuit is added to n
additional antenna units 3-1 to 3-n.
That is, n additional antenna units 3-1 to 3-n are provided,
and an additional reactance circuit is provided in at least one
of the n additional antenna units 3-1.
More specifically, an additional reactance circuit 6D
including a variable-capacitance diode 61D whose capacitance can
be varied by a control voltage Vc is connected between the first
reactance circuit 6A and an additional radiation electrode 9-1,

and a frequency-variable circuit is formed by the first reactance
circuit 6A and the additional reactance circuit 6D. That is,
the additional antenna unit 3-1 is formed by the
frequency-variable circuit, the additional radiation electrode
9-1, and the feed electrode 4.
In the additional antenna unit 3-2, the coil 92 is connected
to an additional radiation electrode 9-2, as in the eighth
embodiment, however no additional reactance circuit is connected.
Thus, the additional antenna unit 3-2 is formed by the feed
electrode 4, the first reactance circuit 6A, and the additional
radiation electrode 9-2.
In the subsequent additional antenna units, an additional
reactance circuit is provided when necessary. In the additional
antenna unit 3-n, which is in the last stage, an additional
reactance circuit 6E is connected to an additional radiation
electrode 9-n. That is, a frequency-variable circuit is formed
by the first reactance circuit 6A and the additional reactance
circuit 6E. Accordingly, the additional antenna unit 3-n is
formed by the feed electrode 4, the frequency-variable circuit,
and the additional radiation electrode 9-n.
With this configuration, as shown by a return-loss curve
S1 represented by a solid line shown in Fig. 18, the resonant
frequencies f1 and f2 of the first and second antenna units 2
and 3 and the resonant frequencies f3 to fn of the additional
antenna units 3-1 to 3-n can be obtained.

As shown by a return-loss curve S2 represented by a broken
line, the resonant frequencies f1, f2, f3, f4, •••, and fn of
the first and second antenna units 2 and 3 and the additional
antenna units 3-1, 3-2, • • • , and 3-n are changed at the same time
by the amounts of change dl, d2, d3, d4, • • • , and dn to the resonant
frequencies f1', f2', f3', f4', •••, and fn'.
Since the frequency-variable circuits of the additional
antenna units 3-1 and 3-n have two reactance circuits (the first
reactance circuit 6A and the additional reactance circuit 6D;
and the first reactance circuit 6A and the additional reactance
circuit 6E), the amounts of change d3 and dn from the resonant
frequencies f3 and fn to the resonant frequencies f3' and fn'
are greater than the amount of change d4 from the resonant
frequency f4 to the resonant frequency f4' of the additional
antenna unit 3-2, which includes only a single reactance circuit
(the first reactance circuit 6A).
Since the other configurations, operations, and advantages
of the antenna device according to this embodiment are similar
to those of the antenna device according to the eighth embodiment,
the description of those similar configurations, operations, and
advantages will be omitted.

CLAIMS
1. An antenna device comprising a first antenna unit including
a feed electrode connected to a feed unit, a first radiation
electrode, and a first frequency-variable circuit connected
between the first radiation electrode and the feed electrode;
and a second antenna unit including the feed electrode, a second
radiation electrode, and a second frequency-variable circuit
connected between the second radiation electrode and the feed
electrode,
wherein the first frequency-variable circuit includes a
first reactance circuit connected to the feed electrode, the
first reactance circuit including a first variable-capacitance
diode whose capacitance is variable using a control voltage; and
a second reactance circuit connected between the first reactance
circuit and the first radiation electrode, the second reactance
circuit including a second variable-capacitance diode whose
capacitance is variable using the control voltage, and
wherein the second frequency-variable circuit includes the
first reactance circuit; and a third reactance circuit connected
between the first reactance circuit and the second radiation
electrode, the third reactance circuit including a third
variable-capacitance diode whose capacitance is variable using
the control voltage.
2. The antenna device according to Claim 1, wherein the second
variable-capacitance diode of the second reactance circuit and

the third variable-capacitance diode of the third reactance
circuit are disposed so as to associate with the first
variable-capacitance diode of the first reactance circuit,
cathodes of the first to third variable-capacitance diodes are
connected to each other, and the control voltage is applied to
a portion where the cathodes are connected to each other.
3. The antenna device according to Claim 1 or 2, wherein:
the first reactance circuit is a series resonant circuit
or a parallel resonant circuit including the first
variable-capacitance diode;
the second reactance circuit is a series resonant circuit
or a parallel resonant circuit including the second
variable-capacitance diode; and
the third reactance circuit is a series resonant circuit
or a parallel resonant circuit including the third
variable-capacitance diode.
4. The antenna device according to Claim 3, wherein:
each of the first to third reactance circuits is configured
as a parallel resonant circuit in which a coil is connected in
parallel to a series circuit including the corresponding
variable-capacitance diode; and
at least one of the coils of the first to third reactance
circuits is set as a choke coil and the corresponding reactance
circuit including the coil serves substantially as a series
resonant circuit.

5. The antenna device according to any one of Claims 1 to 4,
wherein an internal resistance of at least one of the first to
third variable-capacitance diodes is different from internal
resistances of the others of the first to third
variable-capacitance diodes.
6. The antenna device according to any one of Claims 1 to 5,
wherein at least the first antenna unit is formed on a dielectric
substrate.
7. The antenna device according to any one of Claims 1 to 6,
wherein an additional radiation electrode is connected to a stage
subsequent to the first reactance circuit, which is connected
to the feed electrode, and an additional antenna unit is formed
by the additional radiation electrode, the feed electrode, and
the first reactance circuit, which is a frequency-variable
circuit.
8. The antenna device according to any one of Claims 1 to 7,
wherein:
a plurality of additional antenna units are provided; and
in at least one of the plurality of additional antenna units,
an additional reactance circuit including a variable-capacitance
diode whose capacitance is variable using the control voltage
is connected between the first reactance circuit and the
corresponding additional radiation electrode, and a
frequency-variable circuit of the at least one of the plurality
of additional antenna units is formed by the additional reactance

circuit and the first reactance circuit.
9. A wireless communication apparatus comprising the antenna
device according to any one of Claims 1 to 8.

An antenna device and a wireless communication apparatus
that are capable of obtaining a plurality of resonant frequencies
and varying the plurality of resonant frequencies over a wide
range are provided.
A first antenna unit 2 of an antenna device 1 includes a
feed electrode 4, a first radiation electrode 5, and a first
frequency-variable circuit 6-1. The first frequency-variable
circuit 6-1 includes first and second reactance circuits 6A and
6B each including a variable-capacitance diode. A control
voltage Vc is applied to the first frequency-variable circuit
6-1, and the resonant frequency of the first antenna unit 2 can
thus be varied. A second antenna unit 3 includes the feed
electrode 4, a second radiation electrode 7, and a second
frequency-variable circuit 6-2. The second frequency-variable
circuit 6-2 includes first and third reactance circuits 6A and
6C each including a variable-capacitance diode. A control
voltage Vc is applied to the second frequency-variable circuit
6-2, and the resonant frequency of the second antenna unit 3 can
thus be varied.

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Patent Number

272375

Indian Patent Application Number

4782/KOLNP/2008

PG Journal Number

14/2016

Publication Date

01-Apr-2016

Grant Date

30-Mar-2016

Date of Filing

26-Nov-2008

Name of Patentee

MURATA MANUFACTURING CO., LTD

Applicant Address

10-1, HIGASHIKOTARI 1-CHOME, NAGAOKAKYO-SHI, KYOTO-FU

Inventors:

#	Inventor's Name	Inventor's Address
1	KAWAHATA, KAZUNARI	C/O (A170) INTELLECTUAL PROPERTY DEPARTMENT, MURATA MANUFACTURING CO., LTD., 10-1, HIGASHIKOTARI 1-CHOME, NAGAOKAKYO-SHI, KYOTO-FU 617-8555
2	FUJIEDA, SHIGEYUKI	C/O (A170) INTELLECTUAL PROPERTY DEPARTMENT, MURATA MANUFACTURING CO., LTD., 10-1, HIGASHIKOTARI 1-CHOME, NAGAOKAKYO-SHI, KYOTO-FU 617-8555
3	ISHIZUKA, KENICHI	C/O (A170) INTELLECTUAL PROPERTY DEPARTMENT, MURATA MANUFACTURING CO., LTD., 10-1, HIGASHIKOTARI 1-CHOME, NAGAOKAKYO-SHI, KYOTO-FU 617-8555

PCT International Classification Number

H01Q 1/38,H01Q 9/38

PCT International Application Number

PCT/JP2007/058312

PCT International Filing date

2007-04-17

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2006-192433	2006-07-13	Japan