Title of Invention

PRIMARY RADIATOR FOR PARABOLIC ANTENNA, LOW NOISE BLOCK DOWN-CONVERTER, AND SATELLITE-RECEIVING ANTENNA DEVICE

Abstract

ABSTRACT OF THE DISCLOSURE A primary radiator for a parabolic antenna, having a born cap (14) provided at an end opening (12) of a horn antenna body (11), includes a conically-shaped protruding portion (15) made of a dielectric and formed at an inner wall surface of the horn cap (14) toward the end opening (12), and a cylindrically-shaped protruding portion (16) made of a dielectric and disposed coaxially with the conically-shaped protruding portion in such a maimer as to surround an outer periphery of the conically-shaped protruding portion. This configuration makes it possible to provide a primary radiator for a parabolic antenna, having a radiation pattern width adapted to a parabolic antenna having an arbitrary F/D ratio.

Full Text

Primary Radiator for Parabolic Antenna, Low Noise Block Down-Converter, and Satellite-Receiving Antenna Device This nonprovisional application is based on Japanese Patent Application No. 2007-291971 filed on November 9, 2007 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a primary radiator used for a satellite-receiving parabolic antenna, a low noise block down-converter, and a satellite-receiving anterma device. Description of the Background Art A structure of the conventional, commonly-used parabolic antenna will be described based on Fig. 10, and a structure of the conventional primary radiator for a parabolic antenna will be described based on Fig. 11. As shown in Fig. 10, reception of satellite broadcasting by a parabohc antenna is performed such that an approximately 12-GHz band signal SG reflected by a reflector plate 1 of the parabolic antenna is concentrated on an opening of a primary radiator 10. The signal passing through primary radiator 10 is then heterodyned by a Low Noise Block down-converter (LNB) 2 fi-om a 12-GHz band to a 1-GHz band, and the heterodyned signal passes through a coaxial cable 3 and is input to an interior receiver (BS or CS) tuner or a TV (or VTR) 4 embedded therein. Here, primary radiator 10 for a parabolic antenna has the structure shown in Fig. 11. A horn antenna body 11 is formed in a cylindrical manner, and an end opening 12 spreading out in a fan-like maimer is provided with a corrugation 13 for suppressing side lobes in an antenna radiation pattern. Japanese Patent Laying-Open No. 2003-101420 and Japanese Patent Laying-Open No. 2005-192089, for example, disclose an LNB provided with the conventional primary radiator relating to the present invention. A challenge of the invention described in Japanese Patent Laying-Open No. 2003-101420 is to obtain an ability to reduce manufacturing cost and enhance general versatility in a satellite broadcasting-receiving converter that receives radio waves transmitted from a plurality of adjacent satellites. Dielectric feeders are held at two waveguides, respectively, axes of the two waveguides being disposed in parallel with each other. A protruding wall or a large-thickness portion, which serves as a correction portion, is provided at a front side portion of a waterproof cover that covers radiation portions of the dielectric feeders. An object of the invention described in Japanese Patent Laying-Open No. 2005-192089 is to provide a horn, a radio wave-receiving converter, and an antenna, capable of suppressing manufacturing cost increase. A guide horn has a chassis body that includes a waveguide having an opemng, and a dielectric member. The dielectric member is connected to the opemng of the waveguide, and is configured with dielectrics identified as a plurality of members. Conventional primary radiator 10 described above is designed to have a radiation pattern adapting to an F/D ratio of parabolic antenna 1 to be provided. Here, F represents a focal length of the anterma (a distance fi-om a reflector plate of the antenna to a focal point of the anterma), and D represents a diameter of the reflector plate of the antenna. Therefore, if a primary radiator is provided at a parabolic antenna having an F/D ratio different fi-om the designed F/D ratio, a radiation pattern of the primary radiator fails to adapt to the parabohc antenna, resulting in loss of a received signal. Basically, a parabolic antenna having an F/D ratio and a primary radiator designed to adapt to the F/D ratio are combined and provided. In general, however, a parabolic antenna having an F/D ratio and a primary radiator designed to adapt to another F/D ratio are often combined for use depending upon areas where they are to be provided. In an area where a received signal has low intensity, this may also cause poor reception. If primary radiators designed to adapt to F/D ratios of parabolic antennas, respectively, are prepared so as to solve this problem, the number of types of products is inevitably increased, causing disadvantages in development cost and production cost. Further, in a multi-satellite-receiving antenna having a plurality of primary radiators provided in a row at a single LNB, it is extremely difficult to dispose all the primary radiators at positions of focal points of the parabolic antenna even if the parabolic antenna is of a multifocal type, and hence some of the primary radiators have to be provided at a position out of the focal point of the parabolic antenna. Therefore, received signal loss occurs in such primary radiators. These problems have not yet been solved by the structures described in Japanese Patent Laying-Open No. 2003-101420 and Japanese Patent Laying-Open No. 2005-192089. Horn antenna body 11 is formed in a cylindrical manner, and a horn cap 14 is engaged, through press-fit, onto end opening 12 that spreads out in a fan-like manner. The horn cap is for preventing the entry of moisture such as rainwater from an outside to an inside of horn antenna body 11 of the primary radiator. Therefore, an O ring 17 for shutting off water is interposed between end opening 12 of horn antenna body 11 and horn cap 14, so that waterproof function is ensured. Horn cap 14 is formed of a resin such as plastic, and hence has a relatively high dielectric constant with respect to a dielectric constant of air. Therefore, the shape of horn cap 14 exerts a great influence on an input VSWR and a radiation pattern of a device that includes the primary radiator. Here, the VSWR means a Voltage Standing Wave Ratio. SUMMARY OF THE INVENTION The present invention solves the above-described problems. An object of the present invention is to provide a primary radiator for a parabolic antenna, an LNB, and a satellite-receiving antenna, which enable a radiation pattern width to be adapted to a parabolic anteima having an arbitrary F/D ratio, only by replacement of a horn cap. To solve the above-described problems, a primary radiator for a parabolic antenna according to the present invention has, in one aspect, a horn cap provided at an end opening of a horn antenna body. The primary radiator for a parabolic antenna includes; a conically-shaped protruding portion made of a dielectric and formed at an inner wall surface of the horn cap toward the end opening; and a cylindrically-shaped protruding portion made of a dielectric and disposed coaxially with the conically-shaped protruding portion in such a manner as to surround an outer periphery of the conically-shaped protruding portion. According to the present invention, such a configuration makes it possible to adapt a radiation pattern width to a parabolic antenna having an arbitrary F/D ratio only by replacement of a horn cap. A primary radiator for a parabolic antenna according to the present invention has, in another aspect, a plurality of horn antenna bodies integrated such that their central axes are disposed in parallel with one another, and a horn cap provided to collectively cover end openings of the horn antenna bodies. The primary radiator for a parabolic antenna includes: conically-shaped protruding portions made of a dielectric and formed at an inner wall surface of the horn cap toward the end openings, respectively; and cylindrically-shaped protruding portions made of a dielectric and disposed coaxially with the conically-shaped protruding portions, respectively, in such a manner as to surround outer peripheries of the conically-shaped protruding portions, respectively. The center of each of the conically-shaped protruding portions is disposed at a position displaced fi-om the central axis of the corresponding horn antenna body toward the center of the horn cap. Further, the present invention includes various types of embodiments described below. There is provided a horn cap in which the conically-shaped protruding portion and the cylindrically-shaped protruding portion are made of a dielectric material identical to a dielectric material of the horn cap, and the protruding portions are molded integrally with the horn cap. Further, a circular hole is made in the conically-shaped protruding portion of the horn cap at its center. Further, by providing a thread at each of the horn cap and the horn antenna body so that the horn cap and the horn antenna body are made detachable from/attachable to each other, and replacing the horn cap with a horn cap provided with a protrusion having a dimension adapting to a parabolic antenna having a specific F/D ratio, it becomes possible to adapt a single horn antenna to a plurality of paraboUc antennas having different F/D ratios, respectively. Further, there is provided a horn cap in which each of the center of the conically-shaped protruding portion and the center of the cylindrically-shaped protruding portion is disposed at a position displaced fi^om the central axis of the horn antenna body toward an outer peripheral side of the horn antenna body so as to tih the radiation pattern at a specific angle. Further, the horn cap has a rotatable structure without being anchored to the horn antenna body, and the horn cap and the horn antenna body are provided with calibration markings, so that it becomes possible to fi-eely adjust a tilt of the direction of a radiation pattern. In the primary radiator for a parabolic antenna according to the present invention, a horn cap (waterproof cover) is provided at an end opening of the horn antenna body. At the irmer wall surface of the horn cap, there are disposed a conically-shaped protruding portion made of a dielectric and disposed on the central axis of the horn antenna body toward the end opening, and a cylindrically-shaped protruding portion made of a dielectric and disposed coaxially with the central axis of the horn antenna body to surround the outer periphery of the conically-shaped protruding portion. According to the present invention, such a configuration makes it possible to adapt a radiation pattern width to a parabolic antenna havkig an arbitrary F/D ratio, only by replacement of a horn cap, without redesigning the horn antenna. Further, in the primary radiator for a parabolic antenna, provided with a horn cap in which each of the center of the conically-shaped protruding portion and the center of the cylindrically-shaped protruding portion is disposed at a position displaced fi^om the central axis of the horn anterma body toward the outer peripheral side, it becomes possible to tilt the direction of a radiation pattern at a specific angle. According to the present invention, in a multi-satellite compatible LNB and others, it becomes possible to correct a radiation pattern of a primary radiator provided at a position out of a focal point of the parabolic antenna such that the radiation pattern is oriented toward the parabolic antenna, and hence a multi-satellite compatible LNB suitable for a parabolic antenna is implemented. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BKLEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a primary radiator for a parabolic antenna in a first embodiment of the present invention. Fig. 2 is a cross-sectional view of a primary radiator for a parabolic antenna in a first modification of the first embodiment of the present invention. Figs. 3A-3F are comparative diagrams of radiation patterns between a primary radiator for the conventional parabolic antenna and the first modification of the first embodiment of the present invention. Among them, Figs. 3A-3C show radiation patterns at frequencies of 10.7 GHz, 11.8 GHz, and 12.75 GHz, respectively, when the conventional parabolic antenna is used, and Figs. 3D-3F show radiation patterns at the same frequencies as those in Figs. 3A-3C, respectively, when the first modification of the first embodiment is used. Fig. 4 is a partially-cutaway, cross-sectional view of a primary radiator for a parabolic antenna in a second modification of the first embodiment of the present invention. Figs. 5 A, SB, and 5C are plan views of a primary radiator for a parabolic antenna in a third modification of the first embodiment of the present invention, with a protruding portion 15 located at three positions, respectively, and diagrams that show changes in tilt of a radiation pattern in association with an amount of offset of the protrusion. Fig. 6 is a diagram showing that, in a three-satellite-receiving LNB provided with the primary radiators for a parabolic antenna in the third modification of the first embodiment of the present invention, their radiation patterns adapt to the parabolic antenna. Fig. 7A is a fi-ont view that shows a primary radiator for a parabolic antenna in a fourth modification of the first embodiment of the present invention, and Fig. 7B is a plan view for describing a rotation angle R (degree) of the center of protruding portion 15 about the central axis of the horn antenna body. Fig. 8 A is a cross-sectional view of a dual-beam primary radiator for a parabolic antenna in a second embodiment of the present invention, and Fig. 8B is a plan view thereof Fig. 9 is a diagram showing that, in two-satellite-receiving LNB provided with the primary radiators for a parabolic antenna in the second embodiment of the present invention, its radiation patterns adapt to the parabolic antenna. Fig. 10 is a schematic side view of a typical parabolic antenna. Fig. 11 is a transverse cross-sectional view of the conventional primary radiator for a paraboHc antenna. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will hereinafter be described based on the drawings. (First Embodiment) Fig. 1 shows a primary radiator 10 for a paraboUc anterma in a first embodiment of the present invention. In primary radiator 10 for a parabolic anteima in the present embodiment, a horn cap (waterproof cover) 14 formed of a resin such as plastic is provided, by press-fit due to elastic deformation, at an end opening 12 of a horn antenna body 11. At an inner wall surface of horn cap 14, there are provided a conically-shaped protruding portion 15 made of a dielectric and disposed toward end opening 12 on the central axis of horn antenna body 11, and a cylindrically-shaped protruding portion 16 made of a dielectric and disposed coaxially with the central axis of horn antenna body 11 to surround an outer periphery of the conically-shaped protruding portion 15, According to the present embodiment, such a structure makes it possible to adapt a horn antenna to a parabolic antenna having an arbitrary F/D ratio, only by replacement of horn cap 14, without redesigning a radiation pattern width of the horn antenna. Fig. 2 shows a first modification of the first embodiment shown in Fig. 1. In the first modification, at the inner wall surface of horn cap 14, there are provided conically-shaped protruding portion 15 made of a dielectric, disposed on the central axis of horn antenna body 11 to protrude toward horn antenna body 11, and having a circular hole 15a made at its center, and cylindrically-shaped protruding portion 16 made of a dielectric and disposed coaxially with the central axis of horn antenna body 11 to surround the outer periphery of conically-shaped protruding portion 15. Here, if an LNB equipped with a primary radiator designed to adapt to an F/D ratio = 0.6 according to the conventional technique is provided at an antenna having an F/D ratio = 0.66, for example, a C/N ratio is of course deteriorated when compared with the case where an LNB equipped with a primary radiator designed to adapt to an F/D ratio = 0.66 is provided. However, by attaching an LNB equipped with the primary radiator designed to adapt to an F/D ratio = 0.6 according to the present invention as shown in Fig, 2, a C/N ratio is improved by approximately 0.4 dB. Here, the "C/N ratio" refers to a ratio between a carrier wave (carrier) of a signal and a noise where no signal is present. The larger value of the C/N ratio represents that a noise is mixed to the lesser extent. As an example, Figs. 3A-3F show radiation patterns of a horn antenna to which the conventional horn cap is attached, and radiation patterns of a horn antenna to which the horn cap provided with a protrusion of a dielectric as shown in Fig. 2 is provided. Figs. 3A-3C show radiation patterns at fi-equencies of 10,7 GHz, 11.8 GHz, and 12.75 GHz, respectively, when the conventional parabolic antenna is used. Figs. 3D-3F show radiation patterns at the same frequencies as those in Figs. 3 A-3C, respectively, when the first modification of the first embodiment is used. As can be seen from the comparison between radiation patterns in Fig. 3, attachment of the horn cap according to the present embodiment causes smaller radiation pattern widths of the horn antenna, and hence produces radiation patterns that more closely match an antenna having a large F/D ratio, when compared with the conventional one. Further, radiation pattern widths in an E plane and an H plane coincide with each other, and consequently, an effect of improving cross polarization characteristics is achieved as well. Further, if the above-described conically-shaped protrusion is molded integrally with the horn cap, it may be necessary to suppress generation of a sink mark (a recess generated on the outside of the horn cap at a position corresponding to the position of the protrusion on the inside) during molding, by making a hole at the center. However, as shown in Figs. 3A-3F, even if a hole is made at the center, the effect of changing a radiation pattern width can sufficiently be achieved, and hence no problem arises. Next, a second modification of the first embodiment will be described based on Fig. 4. In the second modification, as shown in Fig. 4, horn cap 14 and a corrugation 13 of horn antenna body 11 are provided with threads 14a, 13 a, respectively, such that horn cap 14 and corrugation 13 are structured to be detachable from/attachable to each other. It becomes thereby possible to provide a universal LNB that enables a user to freely attach the same to an arbitrary parabolic antenna by exchange of horn caps at which protrusions having dimensions adapting to various F/Ds are formed, respectively. Next, a third modification of the first embodiment of the present invention will be described based on Figs. 5A-5C. In the third modification, the centers of protrusions 15, 16 made of a dielectric and shown in Fig. 2 are disposed at a position displaced from the central axis of horn antenna body 11 by a distance S toward the outer peripheral side. Figs. 5A-5C show radiation patterns in an E plane and an H plane at a fixed frequency of 11.8 GHz, when the center of protrusion 15 is displaced from the central axis of horn antenna body 11 in a direction of an H plane + by distance S of 0 mm, 4 mm, and 8 mm, respectively. In the present embodiment, as shown in Figs. 5A-5C, it is found that such a structure causes a direction of the radiation pattern to be tilted in accordance with an amount by which the protrusion is offset fi^om the central axis of the horn antenna body. By tilting the direction of the radiation pattern as such, it becomes possible to correct a radiation pattern of a primary radiator provided at a position out of a focal point of a parabolic antenna, such that the radiation pattern is oriented toward the parabolic antenna. Therefore, by tilting the direction of a radiation pattern at a specific angle, it becomes possible to correct a radiation pattern of a primary radiator provided at a position out of a focal point of a parabolic antenna, such that the radiation pattern is oriented toward the parabolic antenna, in a multi-satellite compatible LNB and others as in a three-satellite-receiving antenna shown in Fig. 6. Next, a fourth modification of the first embodiment of the present invention will be described based on Figs. 7A, 7B, In the fourth modification, as shown in Fig. 7A, horn cap 14 is allowed to rotate in a state where the horn cap is screwed or press-fitted without being anchored. It becomes thereby possible to fi-eely adjust a tilt of the direction of the radiation pattern. Further, if calibration markings 14b that represent angles are provided at horn cap 14, and a reference mark 13b is provided at horn antenna body 11, it is possible to check, by visual inspection, by what amount and in what direction the direction of the radiation pattern is tilted. As a resuh, it becomes possible to easily adjust the direction of a radiation pattern such that the radiation pattern is suited to the parabolic antenna. Fig. 7B is a plan view for describing a rotation angle R (degree) of the center of protruding portion 15 about the central axis of the horn antenna body. (Second Embodiment) Next, a second embodiment of the present invention will be described based on Figs. 8 A, 8B. A device shown in Figs. 8 A, 8B is a two-satellite-receiving device as a multi-beam horn antenna of an integral type. In other words, two horn antenna bodies 11 are integrated such that their central axes are made parallel with each other, and one horn cap 14 is provided to collectively cover end openings 12 of the horn antenna bodies. At the inner wall surface of horn cap 14, there are provided conically-shaped protruding portions 15 made of a dielectric and formed toward end openings 12, respectively, and cylindrically-shaped protruding portions 16 made of a dielectric and disposed coaxially with protruding portions 15 to surround outer peripheries of protruding portions 15, respectively. Further, each of the center of each of conically-shaped protruding portions 15 and the center of each of cylindrically-shaped protruding portions 16 is disposed at a position displaced from the central axis of corresponding horn antenna body 11 toward the center of horn cap 14. According to the present embodiment, as shown in Fig. 9, such a structure makes it possible to correct a radiation pattern of a primary radiator provided at a position out of a focal point of a parabolic antenna, such that the radiation pattern is oriented toward the parabolic antenna. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims. WHAT IS CLAIMED IS; 1. A primary radiator for a parabolic antenna, iiaving a horn cap provided at an end opening of a horn antenna body, comprising: a conically-shaped protruding portion made of a dielectric and formed at an inner wall surface of said horn cap toward said end opening; and a cylindrically-shaped protruding portion made of a dielectric and disposed coaxially with the conically-shaped protruding portion in such a manner as to surround an outer periphery of the conically-shaped protruding portion. 2. A primary radiator for a parabolic antenna, having a plurality of horn antenna bodies integrated such that their central axes are disposed in parallel with one another, and having a horn cap provided to collectively cover end openings of said horn antenna bodies, comprising: a plurality of conically-shaped protruding portions made of a dielectric and formed at an irmer wall surface of said horn cap toward said end openings, respectively; and a plurality of cylindrically-shaped protruding portions made of a dielectric and disposed coaxially with the conically-shaped protruding portions, respectively, in such a manner as to surround outer peripheries of the conically-shaped protruding portions, respectively, wherein the center of each of said plurality of conically-shaped protruding portions is disposed at a position displaced from the central axis of the corresponding horn antenna body toward the center of said horn cap. 3. The primary radiator for the parabolic antenna according to claim 1 or 2, wherein said conically-shaped protruding portion and said cylindrically-shaped protruding portion are molded integrally with said horn cap, and made of a dielectric material identical to a dielectric material of said horn cap. 4. The primary radiator for the parabolic antenna according to claim 1 or 2, wherein a circular hole is made in said conically-shaped protruding portion concentrically with the conically-shaped protruding portion. 5. The primary radiator for the parabolic antenna according to claim 1, wherein each of said horn cap and said horn antenna body is provided with a thread so that said horn cap and said horn antenna body are made detachable from/attachable to each other. 6. The primary radiator for the parabolic antenna according to claim 1 or 2, wherein each of the center of said conically-shaped protruding portion and the center of said cylindrically-shaped protruding portion is disposed at a position concentric with the central axis of the corresponding horn antenna body. 7. A low noise block down-converter, comprising the primary radiator for the parabolic antenna recited in claim 1 or 2. 8. A satellite-receiving antenna device, comprising the low noise block down-converter recited in claim 7. 9. The primary radiator for the parabolic antenna according to claim 1, wherein each of the center of said conically-shaped protruding portion and the center of said cylindrically-shaped protruding portion is disposed eccentrically from the central axis of the corresponding horn antenna body toward an outer peripheral side of the horn antenna body. 10. The primary radiator for the parabolic antenna according to claim 9, wherein said horn cap is made rotatable with respect to the horn antenna body, and one of the horn cap and the horn antenna body is provided with calibration markings, and the other of the horn cap and the horn antenna body is provided with a reference mark. 11. A low noise block down-converter, comprising the primary radiator for the parabolic antenna recited in claim 9 or 10. 12. A satellite-receiving antenna device, comprising the low noise block down-converter recited in claim 11. 13. A low noise block down-converter, comprising the primary radiator for the parabolic anterma recited in claim 2. 14. A satellite-receiving antenna device, comprising the low noise block down-converter recited in claim 13.

Documents:

2738-CHE-2008 - Petiton 137 - POR.pdf

2738-CHE-2008 CLAIMS 28-05-2014.pdf

2738-CHE-2008 EXAMINATION REPORT REPLY RECIEVED 28-05-2014.pdf

2738-CHE-2008 FORM-3 28-05-2014.pdf

2738-CHE-2008 OTHERS 28-05-2014.pdf

2738-che-2008 abstract.pdf

2738-che-2008 claims.pdf

2738-che-2008 correspondence-others.pdf

2738-che-2008 description (complete).pdf

2738-che-2008 drawings.pdf

2738-che-2008 form-1.pdf

2738-che-2008 form-18.pdf

2738-che-2008 form-3.pdf

2738-che-2008 form-5.pdf