Title of Invention	A BROADBAND OMNIDIRECTIONAL ANTENNA
Abstract	The invention relates to a broadband antenna, in particular an omnidirectional antenna with the following characteristics : the emitter (15) projects upwards from a base plate or counterweight surface (1); said emitter (15) has a jacket surface extending away from the base plate (1); the base plate (1) is equipped with a cavity (3), in the vicinity of which the foot point (19) of the monopole emitter (15) is electro-galvanically separated from the base plate or the counterweight surface (1); and the emitter (15) is supplied with energy by means of a serial or capacitive inner conductor line coupling.

Title of Invention

A BROADBAND OMNIDIRECTIONAL ANTENNA

Abstract

The invention relates to a broadband antenna, in particular an omnidirectional antenna with the following characteristics : the emitter (15) projects upwards from a base plate or counterweight surface (1); said emitter (15) has a jacket surface extending away from the base plate (1); the base plate (1) is equipped with a cavity (3), in the vicinity of which the foot point (19) of the monopole emitter (15) is electro-galvanically separated from the base plate or the counterweight surface (1); and the emitter (15) is supplied with energy by means of a serial or capacitive inner conductor line coupling.

Full Text	The invention relates to an antenna, in particular an omnidirectional antenna Omnidirectional antennas are known, for example, in the form of so-called indoor antennas which have a multiband capability and preferably transmit and receive vertical polarization. They have a base plate on which an antenna element which is in the form of a monopole projects transversely from, that is to say at right angles to, the base plate. The entire arrangement is generally covered by means of a protective housing (radome). A recess is incorporated in the center, or slightly offset in the vicinity of the center, on the base plate, which is, metallic or at least conductive, and generally has a circular shape in a plan view, in which recess a plug element for a plug connection is anchored, generally a contact element in the form of a plug. A coaxial cable in the form of a second plug element, generally in the form of a plug element in the form of a female connector, can generally be connected there, from the underneath. The outer conductor in this case makes contact with the base plate. The inner conductor of the feed cable is electrically connected via the plug contact that is provided on the base plate to the antenna element, which is in the form of a monopole and projects from the base plate. In other words, the inner conductor is electrically conductively isolated from the base plate, and thus from the outer conductor of a coaxial cable to be connected. Omnidirectional antennas such as these may be designed such that they can transmit and receive simultaneously in two or more frequency ranges, that is to say simultaneously in two or more frequency bands. Indoor omnidirectional antennas of this type have already been produced and marketed by the applicant and, by way of example, these can transmit and receive simultaneously in the following frequency ranges: 824 - 960 MHz 1425 - 1710 MHz 1710 - 1880 MHz 1850 - 1990 MHz 1920 - 2170 MHz Antennas with a multiband capability are likewise known, are produced and marketed by the applicant and, for example, can be operated simultaneously at the following frequencies: 876 - 890 MHz 890 - 960 MHz 1710 - 2170 MHz 2170 - 2500 MHz An antenna forming the generic type is disclosed, for example, in DE 37 09 163 C2 or also in US 4 972 196. The first-mentioned antenna has a rod-shaped antenna which is fed via an inner conductor with the interconnection of a capacitor. The second-mentioned prior publication describes a planar antenna having a disk-shaped antenna element which is fed capacitively in the middle. The object of the present invention is to provide a physically comparatively very small antenna which has a multiband capability, that is to say it has a very broad bandwidth overall, which can also be used as an omnidirectional antenna and which is of simple construction. In this case, the aim is to be able to operate the antenna simultaneously over even wider bandwidths. Accordingly, the present invention provides a broadband omnidirectional antenna comprising: an antenna element in the form of a monopole, the antenna element projecting from a base plate and arranged such that it is electrically conductively isolated from the base plate, the antenna element having at least a first antenna section which widens conically or at least partially conically away from the base plate at a foot point, the base plate having a recess in the area of the foot point, the antenna element comprising a first coupling element and a second coupling element, the first coupling element comprising a rod-like structure, the second coupling element comprising a tubular structure, whereby the first coupling element is inserted into the second coupling element, the first coupling element projecting from the base plate and being isolated from the base plate, the first coupling element being electrically connectable with a feed line, the second coupling element being electrically connected with the antenna element, said first and second coupling elements providing a series or capacitive inner conductor line coupling, the second coupling element being positioned within the antenna element first antenna section. Preferably, the antenna has a feed line wherein the first coupling element extends transversely with respect to and preferably at right angles to the base plate and is electrically connected to the feed line such that it is electrically conductively isolated from the base plate. The first and second coupling elements are electrically conductively connected to or part of the antenna element, said coupling elements not being conductively connected to one another providing series line coupling. The antenna has at least one cylindrical antenna element section. The antenna element first antenna element section widens conically away from the base plate and merges into a cylindrical antenna element section. The second coupling element is part of the antenna element and has a side which faces the base plate, said side being connected to a conical or truncated conical antenna element section, by the interposition of a connecting section running parallel to the base plate. The antenna element operates on a predetermined frequency band centered at a mean wavelength A, and wherein the axial length of the first coupling element is λ/4 - 40% λ/4 + 40% λ/4. The antenna may operate at a mean wavelength A, and wherein the axial length of the first coupling element is (n x λ/4) - 40% (n x λ/4) where n = 1, 3, 5 .... Preferably, the axial length of the first coupling element is designed for the lowermost frequency in one of the two or more frequency bands, such that it is small in comparison to Lambda/4, where Lambda represents the mid- frequency of the relevant frequency band. The antenna element is composed of electrically conductive material. The antenna element comprises an injection-molded plastic part provided with a conductive coating. The first coupling element is positioned within a conical void formed within a conically widening portion of said first antenna section. The first coupling element and the isolator element comprise a unit which can be handled as an entity, the isolator on the first coupling element being composed of a sprayed-on substance. The first coupling element is mounted on a base plate to comprise a unit which can be handled as an entity by means of the isolator element which is located thereon and a plug element anchored on the base plate. The antenna element is preferably covered with a shroud, by means of which the antenna element is protected against axial sliding and radial tilting. The covering device comprises an inner shroud and an outer shroud, the outer shroud covering everything can be fitted on the inner shroud, the outer shroud being anchored on the inner shroud and/or on the reflector via a clipping and/or latching device. The antenna may comprise a reflector and a covering device comprising an inner shroud attached to the reflector by a clipping and/or a latching device. The inner shroud has a central fixing section which projects into the interior of the cup-shaped antenna element, presses against the adjacent end face of the second coupling element and thus protects the antenna element against axial movement and/or radial tilting. In a preferred embodiment, the antenna has a tubular isolator element arranged between the first coupling element and the second coupling element. The isolator element has a radially projecting stop, flange or flange section in the area of the foot point on the antenna element via which the isolator element is supported or held with respect to the base plate. The foot point of the antenna element rests on the flange. The first coupling element is part of a feed conductor and is formed from the inner conductor of a coaxial feed line. The first coupling element is formed from the inner conductor of a coaxial feed line. The present invention also provides a multiband indoor omnidirectional antenna comprising: a base plate; a monopole antenna element projecting from and electrically isolated from the base plate, said monopole antenna element comprising a tubular conical section and a cylindrical section, said tubular conical section operating as a radiator for a first frequency band, said cylindrical section operating as a radiator for a second frequency band lower than said upper frequency band; and a series inner conductor line coupler for feeding the antenna element, said inner conductor line coupler comprising a tubular coupling structure and rod-like coupling structure that is insertable into said tubular coupling structure to couple with said monopole antenna element, the rod-like coupling structure projecting from the base plate and being isolated from the base plate, the rod-like coupling structure being electrically connectable with a feed line, the tubular coupling structure being electrically connected with the antenna element, said rod- like coupling structure and the tubular coupling structure providing a series or capacitive inner conductor line coupling, the series inner conductor line being positioned within the antenna element tubular conical section. Preferably, the antenna operates on a predetermined frequency band having a mean wavelength A, and wherein said coupler has an axial length of λ/4 - 40% λ/4 The antenna operates on a predetermined frequency band having a mean wavelength A, and wherein said coupler has an axial length of (n x λ/4) - 40% (n x λ/4) x λ/4), where n = 1, 3, 5 .... The coupler provides both capacitive coupling and inductive coupling at least at limit frequencies. For some frequencies of interest the electrical length of the coupler is a half wavelength which results in a resonance such that open end at the base of the antenna element acts as an open circuit, and for other frequencies of interest the length of the coupler is short in comparison to quarter wavelength and thus forms a series capacitance allowing broadband impedance matching. The coupler provides capacitive and inductive coupling. The series inner conductor line coupler is positioned within a hollow formed by the tubular conical section. It must be regarded as very surprising that a greatly widened bandwidth for simultaneous operation in widely differing frequency ranges is possible by means of a single physically very small antenna, by the antenna being fed by means of a series or capacitive line coupling at the foot point of the antenna element. Very wide bandwidths are possible in this way. By way of example, the antenna according to the invention can be operated without any problems simultaneously in the 800 to 1000 MHz band, in the 1400 - 3500 MHz band, or else, for example, in the 5000 to 6000 MHz band. Owing to the series (capacitive) line coupling, there may be resonances in the upper band. The antenna according to the invention has a generically specific serial or capacitive coupling. This is so since, according to the invention, a first coupling element which extends away from the base plate surface or from the counterweight surface such that it is electrically conductively isolated from it is provided for the inner conductor coupling. Interacting with it is a second line coupling element, which is electrically conductively connected to the antenna element or is part of the antenna element. The first and second line coupling elements are thus electrically conductively isolated from each other, that is not electrically conductively connected to each other, whereby the serial or capacitive line coupling is brought about. The two interacting coupling elements are on the one hand in the form of a rod and on the other hand in the form of a tube, so that the two coupling elements can be inserted one into the other. This offers the major advantage that the linear design can be used to bring about an optimum capacitive or serial coupling. In addition, by this design, on the other hand a corresponding holding and carrying function can also be brought about for the antenna element, in particular whenever an isolating dielectric is provided between the two interacting coupling elements, whereby the two coupling elements are mechanically held firmly against each other during their conductive isolation. The antenna according to the invention, which is like a monopole, is in this case preferably rotationally symmetrical, or is preferably designed to be rotationally symmetrical at least in specific angle ranges, having at least one section which widens conically in the longitudinal direction of the antenna, which is in the form of a monopole. The antenna may also be designed such that only its external shape is conical, overall. The antenna may thus in principle also be radially symmetrical or may transmit and receive symmetrically, that is to say it may have a cross-sectional shape such that the antenna can be made to be coincident when it is rotated through a specific angle in a plane about a central axis. This may, for example, apply solely to the antenna element or, for example, solely to the base plate, or to both. Alternatively, the antenna element, which is in the form of a monopole or is similar to a monopole, may be cylindrical. The antenna element, which is in the form of a monopole, of the antenna is preferably in a form, however, which is subdivided into a first section, which widens conically away from the base plate, and a cylindrical second section, which is adjacent to it. In other words, according to the present invention, the antenna element is preferably formed from a combination of a conical antenna element section and a cylindrical antenna element section. The conical part of the antenna element primarily acts as a monopole for the upper frequency bands. The cylindrical part of the antenna element in contrast interacts with the associated counterweight surface (base plate) more for the lower frequencies. As a positive feature, it should be noted that this means that no reaction can be found from the cylindrical part on the upper frequency bands. The series and/or capacitive line coupling, which thus comprises a series and/or capacitive inner conductor coupling, is preferably provided via a first coupling part, which is connected to the feed line (inner conductor of a coaxial conductor) , is in the form of a rod and projects from the base plate, isolated from the base plate. The second coupling part, which is coupled to it, is connected to the antenna element, or is part of the antenna element. The second coupling part is preferably tubular. In particular in order to achieve protection against rotation, the coupling part may also be in the form of a polygon or the like, that is to say, for example, it may have an n-sided polygonal cross section. In general terms, the cross-sectional shape may be designed such that it has at least one shape that is not circular. This allows the antenna element, which is similar to a monopole and is formed from a combination of a conical surface and a cylindrical section adjacent to it, to be fitted by- means of its internal tubular section (which projects from the foot point of the antenna element) directly onto the first coupling part, which is in the form of a rod and is connected to the feed cable. Since the first and second coupling parts, that is to say the feed line and the antenna element which is in the form of a monopole, are conductively isolated in order to produce the series line coupling, an isolating sleeve of the first coupling part is preferably fitted, onto which the second coupling part of the antenna element, which is in the form of a monopole, can be fitted. This also results in very simple assembly and installation, since the antenna element can be mounted, without any soldering and just by pushing it on, above the base plate on the first coupling part, which is connected to the feed line, and with the interposition of an insulating isolator. However, the isolator need not necessarily be composed, for example, of a plastic material with a dielectric constant which can be selected in advance. Air may also be used as an isolator. In this case all that is necessary is to use a suitable centering device and/or spacer in order to ensure that the fitted antenna element cannot make an electrically conductive contact with the coupling part under discussion, which is in the form of a rod and projects from the base plate, and/or with the base plate itself. The series feed also makes it possible to minimize the antenna element's height in comparison with the conventional solution. This also makes it possible to reduce the counterweight area (base plate), thus making it possible to achieve a comparatively small physical size. The invention will be explained in more detail in the following text with reference to exemplary embodiments. In this case, in detail: Figure la: shows a schematic plan view of the antenna according to the invention; Figure lb: shows a view from underneath of the antenna according to the invention; Figure 2: shows a schematic vertical cross section through the axial center of the antenna according to the invention; Figure 3: shows a schematic perspective illustration of a coupling part which projects from the base plate 1, is in the form of a rod, and is electrically connected to the feed line; Figure 4: shows a schematic perspective illustration of a first embodiment of an antenna element; Figure 5: shows an axial cross-section illustration through a further modified antenna element shape; Figure 6: shows an axial cross section through a modified conical or truncated conical antenna element shape; Figure 7: shows an axial cross section through the antenna according to the invention in a first fitted inner shroud; and Figure 8: shows a cross-section illustration corresponding to that in Figure 7, in which an outer shroud which covers everything is fitted to the inner shroud. A first exemplary embodiment of an antenna according to the invention and having an antenna element 15 is shown in the form of a schematic plan view in Figure la, in the form of a schematic view from underneath in Figure lb, and in the form of a vertical cross-sectional illustration, passing through the central axis, in Figure 2. The antenna has a base plate or ground plate 1 which, in the illustrated exemplary embodiment, is circular or is in the form of a disk. This base plate or ground plate 1 may, however, also have a completely different shape. For example, it may be square, rectangular, oval etc., that is to say in general it may also be n-sided polygonal or may have other desired basic shapes and boundary lines. The plate 1 is essentially referred to in the following text as the base plate 1. The base plate 1 in this case also, inter alia, carries out the function of a counterweight surface. A recess 3 is incorporated in the center of the base plate 1. A plug element 5 is positioned and attached in and underneath the recess 3 and, in the illustrated exemplary embodiment, is in the form of a coaxial plug element 5' . The outer conductor 7a of the plug element 5 is electrically conductively connected to the base plate 1. The inner conductor 7a of the plug element 5 is passed through the recess 3, isolated from the outer conductor 7b, and is electrically conductively connected to a first or a feed-side coupling element 11 which extends above the base plate 1. This coupling element 11 is transverse with respect to the base plate, that is to say it is vertical in the illustrated exemplary embodiment. It is in the form of a rod and may preferably have a circular cross section. A tubular isolator element 13 is fitted on this coupling element 11. This isolator element 13 in the illustrated exemplary embodiment has a length which corresponds approximately to the axial length of the coupling element 11. The isolator element 13 is provided in the lower end with a flange 13a which projects laterally and which, in the illustrated exemplary embodiment, is likewise circular or is in the form of a disk and is positioned on the base plate 1 in the area of the recess 3. This isolator element 13 is also plugged onto the antenna element 15 which is in the form of a monopole as shown in Figures 1 and 2. The antenna element 15 which is like a monopole has a first antenna section 15a and a second antenna section 15b. The first antenna section 15a is aligned such that it widens conically away from the foot point 19, that is to say its widened conical section points away from the base plate 1. This conical first antenna element section 15a is followed by a second cylindrical antenna element section 15b, with the diameter of the conical antenna element section at the junction between the first and the second antenna element section corresponding to the diameter of the cylindrical antenna element section. The antenna element thus has an outer surface which extends around the longitudinal axis that runs transversely with respect to the base plate. The antenna element 15 is in this case preferably rotationally symmetrical, is partially rotationally symmetrical, or is at least approximately or essentially radially symmetrical or it transmits and receives symmetrically. As is also evident from the cross-section illustration shown in Figure 2, part of the antenna element is a tubular coupling element 15c which is formed in the interior and has a free internal diameter which is equal to or slightly larger than the external diameter of the tubular isolator element 13. This coupling section 15c thus allows the antenna element, which is in the form of a monopole, to be pushed onto the isolator element 13 until the lowermost contact surface 15' of the antenna element 15, that is to say the foot point 19 of the antenna element, rests on the isolator flange 13a of the isolator element 13, and is thus electrically conductively isolated from the base plate 1. The axial length of the coupling element 15c is generally longer than the axial length of the isolator element 13 and/or the length of the first coupling element 11 on the feed cable side. The length of the hollow-cylindrical isolator 13 is in this case comparatively non-critical, and it may also be considerably shorter. The isolator is essentially used only to mechanically hold the antenna element 15 and, furthermore, contributes to no section of the antenna element 15, and in particular not the coupling section 15c, being electrically conductively able to touch the coupling element 11, which is electrically in contact with the inner conductor. The two parallel first and second coupling elements 11 and 15c which are electrically conductively isolated and are even arranged coaxially with respect to one another in the illustrated exemplary embodiment form a series (capacitive) line coupling at the foot point of the antenna element 15, that is to say a series or capacitive inner conductor coupling. The length of the first and second coupling elements 11 and 15c, respectively, should thus preferably be chosen such that the desired optimum coupling can be provided for the various frequency ranges. The coupling element 15c which forms one part of the antenna element arrangement is thus generally chosen to be longer than the length of the coupling element 11 on the feed cable side. The length of the coupling element 11 on the feed side is preferably chosen as a function of the upper frequency bands, such that this length is lambda/4 or n x lambda/4, where n is an odd integer number, that is to say n = 1, 3, 5 .... The open end of the line coupling is thus connected (at the mid-frequency of the respective band) to the feed point 15' via the short circuit, that is to say conductively. The coupling element 11 on the feed cable side is thus both capacitive and inductive at the limit frequencies. For the frequencies for which the length of the coupling element 11 on the feed side is lambda/2, this results in a resonance, that is to say the open end at the foot point 15' of the antenna element 15 acts as an open circuit (high impedance). For the lowermost frequency band (in the illustrated and explained exemplary embodiment, that is to say the band from about 800 to 1000 MHz), the length of the coupling element 11 on the feed cable side is very short in comparison to lambda/4 (that is to say 11 capacitance, which allows broadband impedance matching at this frequency and is also a governing factor for a small physical structure. Figure 3 shows a schematic perspective illustration of the first electrically conductive coupling element 11, which is in the form of a rod, with the antenna element 15 removed, and with the coupling element being electrically conductively connected in the area of the recess 3 to the coaxial plug element that is located on the lower face of the base plate 1, that is to say in the inner conductor plug there. As can be seen from the schematic perspective illustration in Figure 3, the tubular isolator element 13 is just plugged onto this first coupling element 11, is preferably composed of plastic and has a good dielectric constant value. As stated, the second internal tubular element 15c of the antenna element 15 can then be plugged onto this. Figure 4 shows the antenna element 15 on its own, in the form of a perspective illustration, subdivided into a conical antenna element section 15a and a cylindrical antenna element section 15b. Figure 5 shows a schematic cross-section illustration of a modified exemplary embodiment of an antenna element which comprises just one conical antenna element 15, which may have a truncated conical shape. Corresponding to the cross-section illustration shown in Figure 6, this shows that, in this case, only one antenna element, which is cylindrical or is in the form of a pot and is like a monopole, is used as the antenna element 15, and does not have a conical section. In this situation, the coupling element 15c is connected by means of a radial connecting or base section (15d) to the outer casing of the cylindrical antenna element (15) . The coupling section 15c, which forms part of the antenna element arrangement, is seated centrally and internally and is in the form of a hollow cylinder, is shown, in each case in the form of a section, both in the exemplary embodiment in Figure 5 and in Figure 6, and is then plugged onto the first coupling element 11, engaging over it and preferably with the interposition of a hollow-cylindrical isolator. An antenna element as shown in Figure 5 makes it possible to produce a physically small omnidirectional antenna which can be operated in particular in low frequency ranges. An antenna element as shown in Figure 6, that is to say an antenna element which is only conical or in the form of a truncated cone, results in a physically small antenna which can be operated in particular in high frequency bands. Preferably, however, an antenna type having an antenna element as shown in Figures 1 and 2 is provided, whose bandwidth covers both relatively low as well as high and very high frequency ranges and bands. The described antenna type not only makes it possible to produce a very broadband antenna but also, in particular, the serial feed allows the antenna element height to be minimized, thus in turn also allowing the counterweight area (base plate) to be designed to be smaller. The described antennas thus have the advantage that they have a broader bandwidth with a smaller physical size than conventional antennas and, at the same time, can be assembled, installed and produced even more easily, since, in principle, each of the respective antenna elements, with its integrated coupling element 15c, just has to be pushed onto the first coupling element 11, which is electrically connected to the feed line. In principle, there is no need for an isolator element 13 provided only that the antenna element, which is in the form of a monopole, can be arranged with its coupling element 15c electrically conductively isolated from the first coupling element 11. For this purpose, it may be sufficient for the antenna element to be held and fixed only in the area of its foot point on an isolator element which is in the form of a disk or plate, so that the two coupling elements 11 and 15c do not make any electrical contact. In contrast to the illustrated exemplary embodiments, the plug element 5 need not necessarily be a female connector (for example an N female connector). It is also possible to use a permanently connected cable, that is to say in particular with the inner conductor of a coaxial cable being positioned appropriately such that it is used as the coupling element 11 on the feed side, in a corresponding manner to the illustrations in the drawings. The chosen expression "coupling element 11 on the feed side" may thus also be understood as meaning an embodiment in which the coupling element 11 represents the end of a corresponding feed conductor (preferably the end of the inner conductor of a corresponding coaxial feed line cable). Finally, in a further modification, it is likewise possible to provide for the coupling element 11 which is on the feed conductor side, the isolation 13 which surrounds the coupling element 11 and, preferably and furthermore, also the plug element 5 including the inner conductor 7a to be provided and used as a prefabricated unit which can be handled as an entity, is inserted in and is mechanically anchored on a corresponding hole in the base plate 1, in order then just to only fit the antenna element 15 with its coupling element 15c on the antenna element side. As is evident from the cross-section illustration shown in Figures 7 and 8, the reflector has indentations or so-called mounting points 31 which are recessed at a number of points that are located offset from the center, in each of which a hole 33 is incorporated, in order to make it possible to attach the reflector in an appropriate manner to a mount, by the insertion of screws. Finally, the entire antenna arrangement is held and fixed by means of an inner shroud 35. The inner shroud 35 has latching or clipping elements 37 which are located offset in the circumferential direction on the reflector side and can be inserted into corresponding stamped-out areas or openings in the reflector 1. In the snapped-in state, the latching elements 37 then latch behind the stamped areas in the reflector, thus ensuring that the antenna and the inner shroud 37 are held securely, without any further installation measures. In this case, the inner shroud 35 is designed such that, centrally, it has a holding section 37a which engages at the bottom in the cup-shaped antenna element, and whose reflector-side end face 37b secures the antenna element in the plugged-on position. The end face 37b of the inner shroud may in this case touch the upper end face, which faces it, of the coupling element 15c on the antenna element side. This inner shroud thus secures and fixes the antenna element 15 against sliding out axially and thus against radial tilting. Finally, a so-called outer shroud 41 can be fitted such that it covers everything, in which case the outer shroud may likewise latch in via latching or clipping elements 37, which are located internally, for example on a step on the inner shroud in openings that are incorporated there, and/or in openings in the reflector, to be precise such that corresponding latching or clipping elements are passed through the opening and can latch in behind the corresponding material sections of the inner shroud and/or of the reflector. The outer shroud is in this case designed such that it extends over and thus covers everything, including the reflector. The inner shroud 35 and outer shroud 41 are in this case manufactured from a material which is particularly transparent for electromagnetic beams in the frequency range to be transmitted. Finally, it should be noted that the various embodiments of the antenna element 15 do not necessarily need to be composed of conductive material from the start, but that the antenna element 15 may also be formed from other non-conductive material, for example plastic. In this case, the antenna element 15 should have, or else be provided with, a suitable electrically conductive layer on its inner and/or outer surface, or in some other way. WE CLAIM : 1. A broadband omnidirectional antenna comprising: an antenna element in the form of a monopole, the antenna element projecting from a base plate and arranged such that it is electrically conductively isolated from the base plate, the antenna element having at least a first antenna section which widens conically or at least partially conically away from the base plate at a foot point, the base plate having a recess in the area of the foot point, the antenna element comprising a first coupling element and a second coupling element, the first coupling element comprising a rod-like structure, the second coupling element comprising a tubular structure, whereby the first coupling element is inserted into the second coupling element, the first coupling element projecting from the base plate and being isolated from the base plate, the first coupling element being electrically connectable with a feed line, the second coupling element being electrically connected with the antenna element, said first and second coupling elements providing a series or capacitive inner conductor line coupling, the second coupling element being positioned within the antenna element first antenna section. 2. The antenna as claimed in claim 1, having a feed line and wherein the first coupling element extends transversely with respect to and preferably at right angles to the base plate and is electrically connected to the feed line such that it is electrically conductively isolated from the base plate. 3. The antenna as claimed in Claim 1, wherein the first and second coupling elements are electrically conductively connected to or part of the antenna element, said coupling elements not being conductively connected to one another providing series line coupling. 4. The antenna as claimed in claim 1, wherein the antenna has or comprises at least one cylindrical antenna element section. 5. The antenna as claimed in claim 1, wherein the antenna element first antenna element section widens conically away from the base plate and merges into a cylindrical antenna element section. 6. The antenna as claimed in claim 1, wherein the second coupling element is part of the antenna element and has a side which faces the base plate, said side being connected to a conical or truncated conical antenna element section, by the interposition of a connecting section running parallel to the base plate. 7. The antenna as claimed in claim 1, wherein the antenna element operates on a predetermined frequency band centered at a mean wavelength A, and wherein the axial length of the first coupling element is λ/4 - 40% λ/4 4. 8. The antenna as claimed in claim 1, wherein the antenna operates at a mean wavelength A, and wherein the axial length of the first coupling element is (n x λ/4) - 40% (n x λ/4) length 9. The antenna as claimed in claim 1, wherein the axial length of the first coupling element is designed for the lowermost frequency in one of the two or more frequency bands, such that it is small in comparison to Lambda/4, where Lambda represents the mid-frequency of the relevant frequency band. 10. The antenna as claimed in claim 1, wherein the antenna element is composed of electrically conductive material. 11. The antenna as claimed in claim 1, wherein the antenna element comprises an injection-molded plastic part provided with a conductive coating. 12. The antenna as claimed in claim 1, wherein the first coupling element is positioned within a conical void formed within a conically widening portion of said first antenna section. 13. The antenna as claimed in claim 1, wherein the first coupling element and the isolator element comprise a unit which can be handled as an entity, the isolator on the first coupling element being composed of a sprayed-on substance. 14. Antenna as claimed in Claim 13, wherein the first coupling element is mounted on a base plate to comprise a unit which can be handled as an entity by means of the isolator element which is located thereon and a plug element anchored on the base plate. 15. The antenna as claimed in claim 1, wherein the antenna element is covered with a shroud, by means of which the antenna element is protected against axial sliding and radial tilting. 16. The antenna as claimed in Claim 15, wherein the covering device comprises an inner shroud and an outer shroud, the outer shroud covering everything can be fitted on the inner shroud, the outer shroud being anchored on the inner shroud and/or on the reflector via a clipping and/or latching device. 17. The antenna as claimed in claim 19, comprising a reflector and a covering device comprising an inner shroud attached to the reflector by a clipping and/or a latching device. 18. The antenna as claimed in claim 17, wherein the inner shroud has a central fixing section which projects into the interior of the cup-shaped antenna element, presses against the adjacent end face of the second coupling element and thus protects the antenna element against axial movement and/or radial tilting. 19. The antenna as claimed in claim 1 having a tubular isolator element arranged between the first coupling element and the second coupling element. 20. The antenna as claimed in claim 19, wherein the isolator element has a radially projecting stop, flange or flange section in the area of the foot point on the antenna element via which the isolator element is supported or held with respect to the base plate. 21. The antenna as claimed in claim 20, wherein the foot point of the antenna element rests on the flange. 22. The antenna as claimed in claim 21, wherein the first coupling element is part of a feed conductor and is formed from the inner conductor of a coaxial feed line. 23. The antenna as claimed in claim 22, wherein the first coupling element is formed from the inner conductor of a coaxial feed line. 24. A multiband indoor omnidirectional antenna comprising: a base plate; a monopole antenna element projecting from and electrically isolated from the base plate, said monopole antenna element comprising a tubular conical section and a cylindrical section, said tubular conical section operating as a radiator for a first frequency band, said cylindrical section operating as a radiator for a second frequency band lower than said upper frequency band; and a series inner conductor line coupler for feeding the antenna element, said inner conductor line coupler comprising a tubular coupling structure and rod-like coupling structure that is insertable into said tubular coupling structure to couple with said monopole antenna element, the rod-like coupling structure projecting from the base plate and being isolated from the base plate, the rod-like coupling structure being electrically connectable with a feed line, the tubular coupling structure being electrically connected with the antenna element, said rod-like coupling structure and the tubular coupling structure providing a series or capacitive inner conductor line coupling, the series inner conductor line being positioned within the antenna element tubular conical section. 25. The antenna of claim 24 wherein said wherein said antenna operates on a predetermined frequency band having a mean wavelength A, and wherein said coupler has an axial length of λ/ 4 - 40% λ/4 26. The antenna as claimed in claim 24, wherein said antenna operates on a predetermined frequency band having a mean wavelength A, and wherein said coupler has an axial length of (n x λ/4) - 40% (n x λ/4) λ/4), where n = 1, 3, 5 .... 27. The antenna as claimed in claim 24, wherein said coupler provides both capacitive coupling and inductive coupling at least at limit frequencies. 28. The antenna of claim 24 wherein for some frequencies of interest the electrical length of the coupler is a half wavelength which results in a resonance such that open end at the base of the antenna element acts as an open circuit, and for other frequencies of interest the length of the coupler is short in comparison to quarter wavelength and thus forms a series capacitance allowing broadband impedance matching. 29. The antenna of claim 24 wherein said coupler provides capacitive and inductive coupling. 30. The antenna of claim 24 wherein the series inner conductor line coupler is positioned within a hollow formed by the tubular conical section. ABSTRACT A BROADBAND OMNIDIRECTIONAL ANTENNA The invention relates to a broadband antenna, in particular an omnidirectional antenna with the following characteristics : the emitter (15) projects upwards from a base plate or counterweight surface (1); said emitter (15) has a jacket surface extending away from the base plate (1); the base plate (1) is equipped with a cavity (3), in the vicinity of which the foot point (19) of the monopole emitter (15) is electro-galvanically separated from the base plate or the counterweight surface (1); and the emitter (15) is supplied with energy by means of a serial or capacitive inner conductor line coupling.

Full Text

The invention relates to an antenna, in particular an
omnidirectional antenna
Omnidirectional antennas are known, for example, in the
form of so-called indoor antennas which have a
multiband capability and preferably transmit and
receive vertical polarization. They have a base plate
on which an antenna element which is in the form of a
monopole projects transversely from, that is to say at
right angles to, the base plate. The entire arrangement
is generally covered by means of a protective housing
(radome).
A recess is incorporated in the center, or slightly
offset in the vicinity of the center, on the base
plate, which is, metallic or at least conductive, and
generally has a circular shape in a plan view, in which
recess a plug element for a plug connection is
anchored, generally a contact element in the form of a
plug. A coaxial cable in the form of a second plug
element, generally in the form of a plug element in the
form of a female connector, can generally be connected
there, from the underneath. The outer conductor in this
case makes contact with the base plate. The inner
conductor of the feed cable is electrically connected
via the plug contact that is provided on the base plate
to the antenna element, which is in the form of a

monopole and projects from the base plate. In other
words, the inner conductor is electrically conductively
isolated from the base plate, and thus from the outer
conductor of a coaxial cable to be connected.
Omnidirectional antennas such as these may be designed
such that they can transmit and receive simultaneously
in two or more frequency ranges, that is to say
simultaneously in two or more frequency bands.
Indoor omnidirectional antennas of this type have
already been produced and marketed by the applicant
and, by way of example, these can transmit and receive
simultaneously in the following frequency ranges:
824 - 960 MHz
1425 - 1710 MHz
1710 - 1880 MHz
1850 - 1990 MHz
1920 - 2170 MHz
Antennas with a multiband capability are likewise
known, are produced and marketed by the applicant and,
for example, can be operated simultaneously at the
following frequencies:
876 - 890 MHz
890 - 960 MHz
1710 - 2170 MHz
2170 - 2500 MHz
An antenna forming the generic type is disclosed, for
example, in DE 37 09 163 C2 or also in US 4 972 196.
The first-mentioned antenna has a rod-shaped antenna
which is fed via an inner conductor with the
interconnection of a capacitor.
The second-mentioned prior publication describes a

planar antenna having a disk-shaped antenna element
which is fed capacitively in the middle.
The object of the present invention is to provide a
physically comparatively very small antenna which has a
multiband capability, that is to say it has a very
broad bandwidth overall, which can also be used as an
omnidirectional antenna and which is of simple
construction. In this case, the aim is to be able to
operate the antenna simultaneously over even wider
bandwidths.
Accordingly, the present invention provides a broadband
omnidirectional antenna comprising: an antenna element in the
form of a monopole, the antenna element projecting from a base
plate and arranged such that it is electrically conductively
isolated from the base plate, the antenna element having at
least a first antenna section which widens conically or at least
partially conically away from the base plate at a foot point,
the base plate having a recess in the area of the foot point,
the antenna element comprising a first coupling element and a
second coupling element, the first coupling element comprising a
rod-like structure, the second coupling element comprising a
tubular structure, whereby the first coupling element is
inserted into the second coupling element, the first coupling
element projecting from the base plate and being isolated from
the base plate, the first coupling element being electrically
connectable with a feed line, the second coupling element being
electrically connected with the antenna element, said first and
second coupling elements providing a series or capacitive inner
conductor line coupling, the second coupling element being
positioned within the antenna element first antenna section.

Preferably, the antenna has a feed line wherein the first
coupling element extends transversely with respect to and
preferably at right angles to the base plate and is electrically
connected to the feed line such that it is electrically
conductively isolated from the base plate. The first and second
coupling elements are electrically conductively connected to or
part of the antenna element, said coupling elements not being
conductively connected to one another providing series line
coupling. The antenna has at least one cylindrical antenna
element section. The antenna element first antenna element
section widens conically away from the base plate and merges
into a cylindrical antenna element section. The second coupling
element is part of the antenna element and has a side which
faces the base plate, said side being connected to a conical or
truncated conical antenna element section, by the interposition
of a connecting section running parallel to the base plate. The
antenna element operates on a predetermined frequency band
centered at a mean wavelength A, and wherein the axial length of
the first coupling element is λ/4 - 40% λ/4 + 40% λ/4. The antenna may operate at a mean wavelength A, and
wherein the axial length of the first coupling element is (n x
λ/4) - 40% (n x λ/4) where n = 1, 3, 5 .... Preferably, the axial length of the first
coupling element is designed for the lowermost frequency in one
of the two or more frequency bands, such that it is small in
comparison to Lambda/4, where Lambda represents the mid-
frequency of the relevant frequency band. The antenna element is
composed of electrically conductive material. The antenna
element comprises an injection-molded plastic part provided with
a conductive coating. The first coupling element is positioned
within a conical void formed within a conically widening portion

of said first antenna section. The first coupling element and
the isolator element comprise a unit which can be handled as an
entity, the isolator on the first coupling element being
composed of a sprayed-on substance. The first coupling element
is mounted on a base plate to comprise a unit which can be
handled as an entity by means of the isolator element which is
located thereon and a plug element anchored on the base plate.
The antenna element is preferably covered with a shroud, by
means of which the antenna element is protected against axial
sliding and radial tilting. The covering device comprises an
inner shroud and an outer shroud, the outer shroud covering
everything can be fitted on the inner shroud, the outer shroud
being anchored on the inner shroud and/or on the reflector via a
clipping and/or latching device. The antenna may comprise a
reflector and a covering device comprising an inner shroud
attached to the reflector by a clipping and/or a latching
device. The inner shroud has a central fixing section which
projects into the interior of the cup-shaped antenna element,
presses against the adjacent end face of the second coupling
element and thus protects the antenna element against axial
movement and/or radial tilting. In a preferred embodiment, the
antenna has a tubular isolator element arranged between the
first coupling element and the second coupling element. The
isolator element has a radially projecting stop, flange or
flange section in the area of the foot point on the antenna
element via which the isolator element is supported or held with
respect to the base plate. The foot point of the antenna element
rests on the flange. The first coupling element is part of a
feed conductor and is formed from the inner conductor of a
coaxial feed line. The first coupling element is formed from the
inner conductor of a coaxial feed line.

The present invention also provides a multiband indoor
omnidirectional antenna comprising: a base plate; a monopole
antenna element projecting from and electrically isolated from
the base plate, said monopole antenna element comprising a
tubular conical section and a cylindrical section, said tubular
conical section operating as a radiator for a first frequency
band, said cylindrical section operating as a radiator for a
second frequency band lower than said upper frequency band; and
a series inner conductor line coupler for feeding the antenna
element, said inner conductor line coupler comprising a tubular
coupling structure and rod-like coupling structure that is
insertable into said tubular coupling structure to couple with
said monopole antenna element, the rod-like coupling structure
projecting from the base plate and being isolated from the base
plate, the rod-like coupling structure being electrically
connectable with a feed line, the tubular coupling structure
being electrically connected with the antenna element, said rod-
like coupling structure and the tubular coupling structure
providing a series or capacitive inner conductor line coupling,
the series inner conductor line being positioned within the
antenna element tubular conical section.
Preferably, the antenna operates on a predetermined frequency
band having a mean wavelength A, and wherein said coupler has an
axial length of λ/4 - 40% λ/4 The antenna operates on a predetermined frequency band having a
mean wavelength A, and wherein said coupler has an axial length
of (n x λ/4) - 40% (n x λ/4) x λ/4), where n = 1, 3, 5 .... The coupler provides both
capacitive coupling and inductive coupling at least at limit
frequencies. For some frequencies of interest the electrical

length of the coupler is a half wavelength which results in a
resonance such that open end at the base of the antenna element
acts as an open circuit, and for other frequencies of interest
the length of the coupler is short in comparison to quarter
wavelength and thus forms a series capacitance allowing
broadband impedance matching. The coupler provides capacitive
and inductive coupling. The series inner conductor line coupler
is positioned within a hollow formed by the tubular conical
section.
It must be regarded as very surprising that a greatly
widened bandwidth for simultaneous operation in widely
differing frequency ranges is possible by means of a
single physically very small antenna, by the antenna
being fed by means of a series or capacitive line
coupling at the foot point of the antenna element.
Very wide bandwidths are possible in this way. By way
of example, the antenna according to the invention can
be operated without any problems simultaneously in the
800 to 1000 MHz band, in the 1400 - 3500 MHz band, or
else, for example, in the 5000 to 6000 MHz band. Owing
to the series (capacitive) line coupling, there may be
resonances in the upper band.
The antenna according to the invention has a
generically specific serial or capacitive coupling.
This is so since, according to the invention, a first
coupling element which extends away from the base plate
surface or from the counterweight surface such that it
is electrically conductively isolated from it is
provided for the inner conductor coupling. Interacting

with it is a second line coupling element, which is
electrically conductively connected to the antenna
element or is part of the antenna element. The first
and second line coupling elements are thus electrically
conductively isolated from each other, that is not
electrically conductively connected to each other,
whereby the serial or capacitive line coupling is
brought about. The two interacting coupling elements
are on the one hand in the form of a rod and on the
other hand in the form of a tube, so that the two
coupling elements can be inserted one into the other.
This offers the major advantage that the linear design
can be used to bring about an optimum capacitive or
serial coupling. In addition, by this design, on the
other hand a corresponding holding and carrying
function can also be brought about for the antenna
element, in particular whenever an isolating dielectric
is provided between the two interacting coupling
elements, whereby the two coupling elements are
mechanically held firmly against each other during
their conductive isolation.
The antenna according to the invention, which is like a
monopole, is in this case preferably rotationally
symmetrical, or is preferably designed to be
rotationally symmetrical at least in specific angle
ranges, having at least one section which widens
conically in the longitudinal direction of the antenna,
which is in the form of a monopole. The antenna may
also be designed such that only its external shape is
conical, overall.
The antenna may thus in principle also be radially
symmetrical or may transmit and receive symmetrically,
that is to say it may have a cross-sectional shape such
that the antenna can be made to be coincident when it
is rotated through a specific angle in a plane about a
central axis. This may, for example, apply solely to

the antenna element or, for example, solely to the base
plate, or to both.
Alternatively, the antenna element, which is in the
form of a monopole or is similar to a monopole, may be
cylindrical.
The antenna element, which is in the form of a
monopole, of the antenna is preferably in a form,
however, which is subdivided into a first section,
which widens conically away from the base plate, and a
cylindrical second section, which is adjacent to it. In
other words, according to the present invention, the
antenna element is preferably formed from a combination
of a conical antenna element section and a cylindrical
antenna element section. The conical part of the
antenna element primarily acts as a monopole for the
upper frequency bands. The cylindrical part of the
antenna element in contrast interacts with the
associated counterweight surface (base plate) more for
the lower frequencies. As a positive feature, it should
be noted that this means that no reaction can be found
from the cylindrical part on the upper frequency bands.
The series and/or capacitive line coupling, which thus
comprises a series and/or capacitive inner conductor
coupling, is preferably provided via a first coupling
part, which is connected to the feed line (inner
conductor of a coaxial conductor) , is in the form of a
rod and projects from the base plate, isolated from the
base plate. The second coupling part, which is coupled
to it, is connected to the antenna element, or is part
of the antenna element. The second coupling part is
preferably tubular. In particular in order to achieve
protection against rotation, the coupling part may also
be in the form of a polygon or the like, that is to
say, for example, it may have an n-sided polygonal
cross section. In general terms, the cross-sectional
shape may be designed such that it has at least one

shape that is not circular. This allows the antenna
element, which is similar to a monopole and is formed
from a combination of a conical surface and a
cylindrical section adjacent to it, to be fitted by-
means of its internal tubular section (which projects
from the foot point of the antenna element) directly
onto the first coupling part, which is in the form of a
rod and is connected to the feed cable. Since the first
and second coupling parts, that is to say the feed line
and the antenna element which is in the form of a
monopole, are conductively isolated in order to produce
the series line coupling, an isolating sleeve of the
first coupling part is preferably fitted, onto which
the second coupling part of the antenna element, which
is in the form of a monopole, can be fitted.
This also results in very simple assembly and
installation, since the antenna element can be mounted,
without any soldering and just by pushing it on, above
the base plate on the first coupling part, which is
connected to the feed line, and with the interposition
of an insulating isolator.
However, the isolator need not necessarily be composed,
for example, of a plastic material with a dielectric
constant which can be selected in advance. Air may also
be used as an isolator. In this case all that is
necessary is to use a suitable centering device and/or
spacer in order to ensure that the fitted antenna
element cannot make an electrically conductive contact
with the coupling part under discussion, which is in
the form of a rod and projects from the base plate,
and/or with the base plate itself.
The series feed also makes it possible to minimize the
antenna element's height in comparison with the
conventional solution. This also makes it possible to
reduce the counterweight area (base plate), thus making
it possible to achieve a comparatively small physical

size.
The invention will be explained in more detail in the
following text with reference to exemplary embodiments.
In this case, in detail:
Figure la: shows a schematic plan view of the
antenna according to the invention;
Figure lb: shows a view from underneath of the
antenna according to the invention;
Figure 2: shows a schematic vertical cross section
through the axial center of the antenna
according to the invention;
Figure 3: shows a schematic perspective
illustration of a coupling part which
projects from the base plate 1, is in
the form of a rod, and is electrically
connected to the feed line;
Figure 4: shows a schematic perspective
illustration of a first embodiment of an
antenna element;
Figure 5: shows an axial cross-section
illustration through a further modified
antenna element shape;
Figure 6: shows an axial cross section through a
modified conical or truncated conical
antenna element shape;
Figure 7: shows an axial cross section through the
antenna according to the invention in a
first fitted inner shroud; and
Figure 8: shows a cross-section illustration

corresponding to that in Figure 7, in
which an outer shroud which covers
everything is fitted to the inner
shroud.
A first exemplary embodiment of an antenna according to
the invention and having an antenna element 15 is shown
in the form of a schematic plan view in Figure la, in
the form of a schematic view from underneath in
Figure lb, and in the form of a vertical
cross-sectional illustration, passing through the
central axis, in Figure 2.
The antenna has a base plate or ground plate 1 which,
in the illustrated exemplary embodiment, is circular or
is in the form of a disk. This base plate or ground
plate 1 may, however, also have a completely different
shape. For example, it may be square, rectangular, oval
etc., that is to say in general it may also be n-sided
polygonal or may have other desired basic shapes and
boundary lines. The plate 1 is essentially referred to
in the following text as the base plate 1. The base
plate 1 in this case also, inter alia, carries out the
function of a counterweight surface.
A recess 3 is incorporated in the center of the base
plate 1. A plug element 5 is positioned and attached in
and underneath the recess 3 and, in the illustrated
exemplary embodiment, is in the form of a coaxial plug
element 5' . The outer conductor 7a of the plug element
5 is electrically conductively connected to the base
plate 1. The inner conductor 7a of the plug element 5
is passed through the recess 3, isolated from the outer
conductor 7b, and is electrically conductively
connected to a first or a feed-side coupling element 11
which extends above the base plate 1. This coupling
element 11 is transverse with respect to the base
plate, that is to say it is vertical in the illustrated
exemplary embodiment. It is in the form of a rod and

may preferably have a circular cross section.
A tubular isolator element 13 is fitted on this
coupling element 11. This isolator element 13 in the
illustrated exemplary embodiment has a length which
corresponds approximately to the axial length of the
coupling element 11. The isolator element 13 is
provided in the lower end with a flange 13a which
projects laterally and which, in the illustrated
exemplary embodiment, is likewise circular or is in the
form of a disk and is positioned on the base plate 1 in
the area of the recess 3.
This isolator element 13 is also plugged onto the
antenna element 15 which is in the form of a monopole
as shown in Figures 1 and 2.
The antenna element 15 which is like a monopole has a
first antenna section 15a and a second antenna section
15b. The first antenna section 15a is aligned such that
it widens conically away from the foot point 19, that
is to say its widened conical section points away from
the base plate 1. This conical first antenna element
section 15a is followed by a second cylindrical antenna
element section 15b, with the diameter of the conical
antenna element section at the junction between the
first and the second antenna element section
corresponding to the diameter of the cylindrical
antenna element section. The antenna element thus has
an outer surface which extends around the longitudinal
axis that runs transversely with respect to the base
plate. The antenna element 15 is in this case
preferably rotationally symmetrical, is partially
rotationally symmetrical, or is at least approximately
or essentially radially symmetrical or it transmits and
receives symmetrically.
As is also evident from the cross-section illustration
shown in Figure 2, part of the antenna element is a

tubular coupling element 15c which is formed in the
interior and has a free internal diameter which is
equal to or slightly larger than the external diameter
of the tubular isolator element 13. This coupling
section 15c thus allows the antenna element, which is
in the form of a monopole, to be pushed onto the
isolator element 13 until the lowermost contact surface
15' of the antenna element 15, that is to say the foot
point 19 of the antenna element, rests on the isolator
flange 13a of the isolator element 13, and is thus
electrically conductively isolated from the base plate
1.
The axial length of the coupling element 15c is
generally longer than the axial length of the isolator
element 13 and/or the length of the first coupling
element 11 on the feed cable side. The length of the
hollow-cylindrical isolator 13 is in this case
comparatively non-critical, and it may also be
considerably shorter. The isolator is essentially used
only to mechanically hold the antenna element 15 and,
furthermore, contributes to no section of the antenna
element 15, and in particular not the coupling section
15c, being electrically conductively able to touch the
coupling element 11, which is electrically in contact
with the inner conductor.
The two parallel first and second coupling elements 11
and 15c which are electrically conductively isolated
and are even arranged coaxially with respect to one
another in the illustrated exemplary embodiment form a
series (capacitive) line coupling at the foot point of
the antenna element 15, that is to say a series or
capacitive inner conductor coupling. The length of the
first and second coupling elements 11 and 15c,
respectively, should thus preferably be chosen such
that the desired optimum coupling can be provided for
the various frequency ranges. The coupling element 15c
which forms one part of the antenna element arrangement

is thus generally chosen to be longer than the length
of the coupling element 11 on the feed cable side. The
length of the coupling element 11 on the feed side is
preferably chosen as a function of the upper frequency
bands, such that this length is lambda/4 or n x
lambda/4, where n is an odd integer number, that is to
say n = 1, 3, 5 .... The open end of the line coupling
is thus connected (at the mid-frequency of the
respective band) to the feed point 15' via the short
circuit, that is to say conductively. The coupling
element 11 on the feed cable side is thus both
capacitive and inductive at the limit frequencies. For
the frequencies for which the length of the coupling
element 11 on the feed side is lambda/2, this results
in a resonance, that is to say the open end at the foot
point 15' of the antenna element 15 acts as an open
circuit (high impedance). For the lowermost frequency
band (in the illustrated and explained exemplary
embodiment, that is to say the band from about 800 to
1000 MHz), the length of the coupling element 11 on the
feed cable side is very short in comparison to lambda/4
(that is to say 11 capacitance, which allows broadband impedance matching
at this frequency and is also a governing factor for a
small physical structure.
Figure 3 shows a schematic perspective illustration of
the first electrically conductive coupling element 11,
which is in the form of a rod, with the antenna element
15 removed, and with the coupling element being
electrically conductively connected in the area of the
recess 3 to the coaxial plug element that is located on
the lower face of the base plate 1, that is to say in
the inner conductor plug there.
As can be seen from the schematic perspective
illustration in Figure 3, the tubular isolator element
13 is just plugged onto this first coupling element 11,
is preferably composed of plastic and has a good

dielectric constant value. As stated, the second
internal tubular element 15c of the antenna element 15
can then be plugged onto this.
Figure 4 shows the antenna element 15 on its own, in
the form of a perspective illustration, subdivided into
a conical antenna element section 15a and a cylindrical
antenna element section 15b.
Figure 5 shows a schematic cross-section illustration
of a modified exemplary embodiment of an antenna
element which comprises just one conical antenna
element 15, which may have a truncated conical shape.
Corresponding to the cross-section illustration shown
in Figure 6, this shows that, in this case, only one
antenna element, which is cylindrical or is in the form
of a pot and is like a monopole, is used as the antenna
element 15, and does not have a conical section. In
this situation, the coupling element 15c is connected
by means of a radial connecting or base section (15d)
to the outer casing of the cylindrical antenna element
(15) .
The coupling section 15c, which forms part of the
antenna element arrangement, is seated centrally and
internally and is in the form of a hollow cylinder, is
shown, in each case in the form of a section, both in
the exemplary embodiment in Figure 5 and in Figure 6,
and is then plugged onto the first coupling element 11,
engaging over it and preferably with the interposition
of a hollow-cylindrical isolator.
An antenna element as shown in Figure 5 makes it
possible to produce a physically small omnidirectional
antenna which can be operated in particular in low
frequency ranges. An antenna element as shown in Figure
6, that is to say an antenna element which is only
conical or in the form of a truncated cone, results in

a physically small antenna which can be operated in
particular in high frequency bands. Preferably,
however, an antenna type having an antenna element as
shown in Figures 1 and 2 is provided, whose bandwidth
covers both relatively low as well as high and very
high frequency ranges and bands.
The described antenna type not only makes it possible
to produce a very broadband antenna but also, in
particular, the serial feed allows the antenna element
height to be minimized, thus in turn also allowing the
counterweight area (base plate) to be designed to be
smaller. The described antennas thus have the advantage
that they have a broader bandwidth with a smaller
physical size than conventional antennas and, at the
same time, can be assembled, installed and produced
even more easily, since, in principle, each of the
respective antenna elements, with its integrated
coupling element 15c, just has to be pushed onto the
first coupling element 11, which is electrically
connected to the feed line.
In principle, there is no need for an isolator element
13 provided only that the antenna element, which is in
the form of a monopole, can be arranged with its
coupling element 15c electrically conductively isolated
from the first coupling element 11. For this purpose,
it may be sufficient for the antenna element to be held
and fixed only in the area of its foot point on an
isolator element which is in the form of a disk or
plate, so that the two coupling elements 11 and 15c do
not make any electrical contact.
In contrast to the illustrated exemplary embodiments,
the plug element 5 need not necessarily be a female
connector (for example an N female connector). It is
also possible to use a permanently connected cable,
that is to say in particular with the inner conductor
of a coaxial cable being positioned appropriately such

that it is used as the coupling element 11 on the feed
side, in a corresponding manner to the illustrations in
the drawings. The chosen expression "coupling element
11 on the feed side" may thus also be understood as
meaning an embodiment in which the coupling element 11
represents the end of a corresponding feed conductor
(preferably the end of the inner conductor of a
corresponding coaxial feed line cable).
Finally, in a further modification, it is likewise
possible to provide for the coupling element 11 which
is on the feed conductor side, the isolation 13 which
surrounds the coupling element 11 and, preferably and
furthermore, also the plug element 5 including the
inner conductor 7a to be provided and used as a
prefabricated unit which can be handled as an entity,
is inserted in and is mechanically anchored on a
corresponding hole in the base plate 1, in order then
just to only fit the antenna element 15 with its
coupling element 15c on the antenna element side.
As is evident from the cross-section illustration shown
in Figures 7 and 8, the reflector has indentations or
so-called mounting points 31 which are recessed at a
number of points that are located offset from the
center, in each of which a hole 33 is incorporated, in
order to make it possible to attach the reflector in an
appropriate manner to a mount, by the insertion of
screws.
Finally, the entire antenna arrangement is held and
fixed by means of an inner shroud 35. The inner shroud
35 has latching or clipping elements 37 which are
located offset in the circumferential direction on the
reflector side and can be inserted into corresponding
stamped-out areas or openings in the reflector 1. In
the snapped-in state, the latching elements 37 then
latch behind the stamped areas in the reflector, thus
ensuring that the antenna and the inner shroud 37 are

held securely, without any further installation
measures.
In this case, the inner shroud 35 is designed such
that, centrally, it has a holding section 37a which
engages at the bottom in the cup-shaped antenna
element, and whose reflector-side end face 37b secures
the antenna element in the plugged-on position. The end
face 37b of the inner shroud may in this case touch the
upper end face, which faces it, of the coupling element
15c on the antenna element side. This inner shroud thus
secures and fixes the antenna element 15 against
sliding out axially and thus against radial tilting.
Finally, a so-called outer shroud 41 can be fitted such
that it covers everything, in which case the outer
shroud may likewise latch in via latching or clipping
elements 37, which are located internally, for example
on a step on the inner shroud in openings that are
incorporated there, and/or in openings in the
reflector, to be precise such that corresponding
latching or clipping elements are passed through the
opening and can latch in behind the corresponding
material sections of the inner shroud and/or of the
reflector. The outer shroud is in this case designed
such that it extends over and thus covers everything,
including the reflector.
The inner shroud 35 and outer shroud 41 are in this
case manufactured from a material which is particularly
transparent for electromagnetic beams in the frequency
range to be transmitted.
Finally, it should be noted that the various
embodiments of the antenna element 15 do not
necessarily need to be composed of conductive material
from the start, but that the antenna element 15 may
also be formed from other non-conductive material, for
example plastic. In this case, the antenna element 15

should have, or else be provided with, a suitable
electrically conductive layer on its inner and/or outer
surface, or in some other way.

WE CLAIM :
1. A broadband omnidirectional antenna comprising:
an antenna element in the form of a monopole, the antenna
element projecting from a base plate and arranged such that it
is electrically conductively isolated from the base plate, the
antenna element having at least a first antenna section which
widens conically or at least partially conically away from the
base plate at a foot point,
the base plate having a recess in the area of the foot
point,
the antenna element comprising a first coupling element and
a second coupling element,
the first coupling element comprising a rod-like structure,
the second coupling element comprising a tubular structure,
whereby the first coupling element is inserted into the second
coupling element,
the first coupling element projecting from the base plate
and being isolated from the base plate, the first coupling
element being electrically connectable with a feed line,
the second coupling element being electrically connected
with the antenna element,
said first and second coupling elements providing a series
or capacitive inner conductor line coupling,
the second coupling element being positioned within the
antenna element first antenna section.
2. The antenna as claimed in claim 1, having a feed line and
wherein the first coupling element extends transversely with
respect to and preferably at right angles to the base plate and
is electrically connected to the feed line such that it is
electrically conductively isolated from the base plate.

3. The antenna as claimed in Claim 1, wherein the first and
second coupling elements are electrically conductively connected
to or part of the antenna element, said coupling elements not
being conductively connected to one another providing series
line coupling.
4. The antenna as claimed in claim 1, wherein the antenna has
or comprises at least one cylindrical antenna element section.
5. The antenna as claimed in claim 1, wherein the antenna
element first antenna element section widens conically away from
the base plate and merges into a cylindrical antenna element
section.
6. The antenna as claimed in claim 1, wherein the second
coupling element is part of the antenna element and has a side
which faces the base plate, said side being connected to a
conical or truncated conical antenna element section, by the
interposition of a connecting section running parallel to the
base plate.
7. The antenna as claimed in claim 1, wherein the antenna
element operates on a predetermined frequency band centered at a
mean wavelength A, and wherein the axial length of the first
coupling element is λ/4 - 40% λ/4 4.
8. The antenna as claimed in claim 1, wherein the antenna
operates at a mean wavelength A, and wherein the axial length of
the first coupling element is (n x λ/4) - 40% (n x λ/4) length
9. The antenna as claimed in claim 1, wherein the axial length
of the first coupling element is designed for the lowermost
frequency in one of the two or more frequency bands, such that
it is small in comparison to Lambda/4, where Lambda represents
the mid-frequency of the relevant frequency band.
10. The antenna as claimed in claim 1, wherein the antenna
element is composed of electrically conductive material.
11. The antenna as claimed in claim 1, wherein the antenna
element comprises an injection-molded plastic part provided with
a conductive coating.
12. The antenna as claimed in claim 1, wherein the first
coupling element is positioned within a conical void formed
within a conically widening portion of said first antenna
section.
13. The antenna as claimed in claim 1, wherein the first
coupling element and the isolator element comprise a unit which
can be handled as an entity, the isolator on the first coupling
element being composed of a sprayed-on substance.
14. Antenna as claimed in Claim 13, wherein the first coupling
element is mounted on a base plate to comprise a unit which can
be handled as an entity by means of the isolator element which
is located thereon and a plug element anchored on the base
plate.
15. The antenna as claimed in claim 1, wherein the antenna
element is covered with a shroud, by means of which the antenna
element is protected against axial sliding and radial tilting.

16. The antenna as claimed in Claim 15, wherein the covering
device comprises an inner shroud and an outer shroud, the outer
shroud covering everything can be fitted on the inner shroud,
the outer shroud being anchored on the inner shroud and/or on
the reflector via a clipping and/or latching device.
17. The antenna as claimed in claim 19, comprising a reflector
and a covering device comprising an inner shroud attached to the
reflector by a clipping and/or a latching device.
18. The antenna as claimed in claim 17, wherein the inner
shroud has a central fixing section which projects into the
interior of the cup-shaped antenna element, presses against the
adjacent end face of the second coupling element and thus
protects the antenna element against axial movement and/or
radial tilting.
19. The antenna as claimed in claim 1 having a tubular isolator
element arranged between the first coupling element and the
second coupling element.
20. The antenna as claimed in claim 19, wherein the isolator
element has a radially projecting stop, flange or flange section
in the area of the foot point on the antenna element via which
the isolator element is supported or held with respect to the
base plate.
21. The antenna as claimed in claim 20, wherein the foot point
of the antenna element rests on the flange.

22. The antenna as claimed in claim 21, wherein the first
coupling element is part of a feed conductor and is formed from
the inner conductor of a coaxial feed line.
23. The antenna as claimed in claim 22, wherein the first
coupling element is formed from the inner conductor of a coaxial
feed line.
24. A multiband indoor omnidirectional antenna comprising:
a base plate;
a monopole antenna element projecting from and electrically
isolated from the base plate, said monopole antenna element
comprising a tubular conical section and a cylindrical section,
said tubular conical section operating as a radiator for a first
frequency band, said cylindrical section operating as a radiator
for a second frequency band lower than said upper frequency
band; and
a series inner conductor line coupler for feeding the
antenna element, said inner conductor line coupler comprising a
tubular coupling structure and rod-like coupling structure that
is insertable into said tubular coupling structure to couple
with said monopole antenna element,
the rod-like coupling structure projecting from the base
plate and being isolated from the base plate, the rod-like
coupling structure being electrically connectable with a feed
line,
the tubular coupling structure being electrically connected
with the antenna element,
said rod-like coupling structure and the tubular coupling
structure providing a series or capacitive inner conductor line
coupling,

the series inner conductor line being positioned within the
antenna element tubular conical section.
25. The antenna of claim 24 wherein said wherein said antenna
operates on a predetermined frequency band having a mean
wavelength A, and wherein said coupler has an axial length of λ/
4 - 40% λ/4 26. The antenna as claimed in claim 24, wherein said antenna
operates on a predetermined frequency band having a mean
wavelength A, and wherein said coupler has an axial length of (n
x λ/4) - 40% (n x λ/4) λ/4), where n = 1, 3, 5 ....
27. The antenna as claimed in claim 24, wherein said coupler
provides both capacitive coupling and inductive coupling at
least at limit frequencies.
28. The antenna of claim 24 wherein for some frequencies of
interest the electrical length of the coupler is a half
wavelength which results in a resonance such that open end at
the base of the antenna element acts as an open circuit, and for
other frequencies of interest the length of the coupler is short
in comparison to quarter wavelength and thus forms a series
capacitance allowing broadband impedance matching.
29. The antenna of claim 24 wherein said coupler provides
capacitive and inductive coupling.
30. The antenna of claim 24 wherein the series inner conductor
line coupler is positioned within a hollow formed by the tubular
conical section.

ABSTRACT

A BROADBAND OMNIDIRECTIONAL ANTENNA
The invention relates to a broadband antenna, in particular an omnidirectional
antenna with the following characteristics : the emitter (15) projects upwards from a base
plate or counterweight surface (1); said emitter (15) has a jacket surface extending away
from the base plate (1); the base plate (1) is equipped with a cavity (3), in the vicinity of
which the foot point (19) of the monopole emitter (15) is electro-galvanically separated
from the base plate or the counterweight surface (1); and the emitter (15) is supplied with
energy by means of a serial or capacitive inner conductor line coupling.

A BROADBAND OMNIDIRECTIONAL ANTENNA

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