Patent Grant
8508421
This invention relates to radio-frequency antenna structures and, more particularly, to low-profile hardened wave-guide antennas.
Mobile radio communications presently mainly rely on conventional whip-type antennas mounted to the roof, hood, or trunk of a motor vehicle. Although whip antennas generally provide acceptable mobile communications performance, they have a number of disadvantages. For example, a whip antenna must be mounted on an exterior surface of the vehicle, so that the antenna is unprotected from the weather, and may for example, be damaged by vehicle washes, unless temporarily removed.
The user of mobile radio equipment is often plagued today by the problem of vandalism of car radio antennas and burglary of the equipment. Indeed, the presence of a whip antenna on the exterior of a car is a good clue to thieves that a radio, telephone transceiver or other equipment is installed within the vehicle.
Varieties of covert antennas are known in the art. Such antennas are usually substantially flush-mounted to a vehicle, covered with fiberglass and refinished to blend with the rest of the car body. In particular, annular slot-type stripline antennas can be useful, as where such an antenna is to be substantially flush-mounted to a vehicle. One such annular slot-type stripline antenna element is described in U.S. Pat. No. 3,665,480. As discussed therein, the antenna element includes a pair of parallel conductive plates formed on opposite faces of a dielectric support structure, one of which has formed therein a generally annular radiating slot of substantially uniform width, and a feed element disposed between the parallel plates and extending radially into the central region of the annular slot for feeding electromagnetic energy into such a slot.
U.S. Pat. No. 4,821,040 describes a compact quarter-wavelength microstrip element especially suited for use as a mobile radio antenna. The antenna is not visible to a passerby observer when installed, since it is literally part of the vehicle. The microstrip radiating element is conformal to a passenger vehicle, and may, for example, be mounted under a plastic roof between the roof and the headliner.
U.S. Pat. No. 4,821,042 describes a vehicle antenna system including high frequency pickup type antennas concealed within the vehicle body for receiving broadcast waves. The high frequency pickups are arranged on the vehicle body at locations spaced apart from one another, that is, at least one adjacent to the vehicle roof and the other on a trunk hinge.
U.S. Pat. No. 5,402,134 describes a flat plate antenna module for use in a non-conductive cab of a motor vehicle and includes a dielectric substrate and one or more antenna loops arranged on the substrate. The substrate is adapted to be installed between the headliner of a cab and the dielectric roof. The module may include a CB antenna loop, an AM/FM antenna loop, a cellular mobile telephone antenna loop, and a global positioning system antenna, without the need for any antenna structure external to the cab. The antennae are arranged on the module in a nested configuration.
U.S. Pat. No. 6,023,243 describes a flat panel antenna for microwave transmission. The antenna comprises at least one printed circuit board, and has active elements including radiating elements and transmission lines. There is at least one ground plane for the radiating elements and at least one surface serving as a ground plane for the transmission lines. The panel is arranged such that the spacing between the radiating elements and their respective groundplane is independent of the spacing between the transmission lines and their respective groundplane. A radome may additionally be provided which comprises laminations of polyolefin and an outer skin of polypropylene.
Despite the prior art in the area of covert antennas, there is still a need in the art for further improvement in order to provide an antenna that might be substantially flush-mounted to a vehicle, has broad band performance and a reduced aperture. It would also be advantageous to have an antenna that would be sufficiently hardened in order to withstand vandalism, and harsh weather conditions. There is also a need and it would be advantageous to have an antenna that can survive the impact of road pebbles, gravel and other objects that can impact the antenna during exploitation.
The present invention partially eliminates disadvantages of cited reference techniques and provides a novel antenna element that is substantially covert and difficult to detect and vandalize.
According to one embodiment, the antenna element includes a waveguide configured for operating in a below-cutoff mode, an exciter configured for exciting the waveguide, and a shield configured for protecting the exciter. The waveguide has a cavity. The shield includes a holder arranged within the cavity, and a front plate mounted on the holder and disposed over at least a part of the exciter. A gap between the inner walls of the waveguide and the front plate defines an aperture of the waveguide. Preferably, the front plate is substantially flush with the aperture.
According to one embodiment, the exciter includes a printed-circuit antenna arranged within the cavity and configured for feeding the waveguide, and a feed arrangement coupled to the printed-circuit antenna at a feed point for providing radio frequency energy to the printed-circuit antenna. The printed-circuit antenna has a layered structure and includes a thin layer of a dielectric material, a patch printed on an under-side of the thin layer, and a substrate arranged between the patch and a bottom of the cavity. The patch includes an orifice that defines the location of the feed point.
According to one embodiment, the orifice is arranged at a verge of the patch, which is the distant edge from the center of the patch. According to one embodiment, the orifice is arranged within the solid portion of the patch.
According to one embodiment, the printed-circuit antenna also includes a pad and a stub coupled to the pad. The pad and stub are both printed on the upper side of the thin layer and arranged under the orifice of the patch.
According to an embodiment, the waveguide is a circular waveguide. In this case, the patch, the thin layer and the substrate all have ring shapes hollowed out in the ring center to define a lumen.
According to an embodiment, the holder of the shield is inserted through the lumen in the center of the layered structure formed by the patch, the thin layer and the substrate.
According to an embodiment, the holder has a tubular shape and includes a tapered portion and a uniform portion. The tapered portion is tapered with contraction from the front plate towards a uniform portion located at the bottom of the cavity. The contraction of the holder extends from the front plate until the location of the printed-circuit antenna. The uniform portion can have a base threaded into the bottom of the cavity.
According to an embodiment, the feed arrangement includes a pin and a sleeve arranged within the substrate between the patch and the bottom of the cavity. The pin passes through a common hole arranged within the waveguide at the bottom of the cavity, the sleeve and the thin layer. The pin is connected to the pad at the feed point of the printed-circuit antenna.
According to an embodiment, the pin is surrounded with an isolator layer. The isolator layer can, for example, be made of teflon.
According to a further embodiment, the antenna element further comprises a radome mounted on the top of the antenna element over the aperture.
According to another aspect of the present invention, there is provided a phased array antenna that comprises a plurality of the antenna elements described above, and a beam steering system coupled to the antenna elements and configured for steering an energy beam produced by said phased array antenna.
According to one embodiment, the waveguides of the antenna elements are arranged in a common conductive ground plane and spaced apart at a predetermined distance from each other.
According to another embodiment, the antenna elements have individual waveguides. Each waveguide is arranged in an individual conductive ground plane and spaced apart at a predetermined distance from each other.
The antenna element of the present invention has many of the advantages of the prior art techniques, while simultaneously overcoming some of the disadvantages normally associated therewith.
The antenna element of the present invention can generally be configured to operate in a broad band within the frequency range of about 20 MHz to 80 GHz.
The antenna element according to the present invention may be efficiently manufactured. The printed circuit part of the antenna (e.g., exciter) can, for example, be manufactured by using printed circuit techniques.
The installation of the antenna element and antenna array of the present invention is relatively quick and easy and can be accomplished without substantial altering a vehicle in which it is to be installed.
The antenna element according to the present invention is of durable and reliable construction.
The antenna element according to the present invention may be readily conformed to complexly shaped surfaces and contours of a mounting platform. In particular, it can be readily conformable to a car or other structures.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows hereinafter may be better understood. Additional details and advantages of the invention will be set forth in the detailed description, and in part will be appreciated from the description, or may be learned by practice of the invention.
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
The principles of the antenna according to the present invention may be better understood with reference to the drawings and the accompanying description, wherein like reference numerals have been used throughout to designate identical elements. It being understood that these drawings which are not necessarily to scale, are given for illustrative purposes only and are not intended to limit the scope of the invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. Those versed in the art should appreciate that many of the examples provided have suitable alternatives which may be utilized.
Referring now to the drawings,
Preferably, but not mandatory, the waveguide 11 is a circular waveguide. It should be noted that using a circular waveguide has a number of distinct advantages. One advantage is that a circular waveguide, owing to its symmetry, can operate in any polarization. From a mechanical point of view the circular waveguide is appropriate because of its mechanical simplicity and hardness.
The antenna element 10 also includes a shield (shown schematically by a reference numeral 17) configured to protect the printed-circuit antenna 15, for example, from vandalism, impact of road pebbles and gravel, and/or from other damaging actions. The shield 17 includes a holder 171 arranged within the cavity 13, and a front plate 172 mounted on the holder 171. A gap between the inner walls of the waveguide 11 and the front plate 172 defines an aperture 14 of the waveguide 11.
When the waveguide 11 is a circular waveguide, the front plate 172 preferably has a shape of a disk. It should be noted that the shield 17 has a twofold purpose. Electrically, the shield causes the antenna to operate the antenna above the cutoff frequency. This function of the shield is in addition to protecting the antenna from foreign elements.
According to one embodiment, the holder 171 has a tubular shape and includes a tapered portion 173 having a varied diameter, and a uniform portion 174 having a uniform diameter. The tapered portion 173 is tapered with contraction from the front plate (disk) 172 towards a uniform portion 174 that is located at a bottom 131 of the cavity 13.
When the waveguide 11 is a circular waveguide, the printed-circuit antenna 15 has a ring shape with a circular lumen 150 arranged in the center of the ring. As shown in
According to an embodiment, the uniform portion 174 of the holder 171 is attached to the bottom 131 of the cavity 13. The connection of the holder 171 to the bottom 131 can, for example, be made with a laser weld, plasma weld pulse, electromagnetic weld or other welding process. Moreover, such fixing may be done by soldering, brazing, crimping, application of glues or by any other known technique depending on the material selected for each component. When desired, the holder 171 can include a base 175 of the uniform portion 174 that can be threaded into the waveguide 13 at the bottom 131 of the cavity 13. When desired, the base 175 of the holder 171 can have a screw thread for screwing the shield 17 to the waveguide 13 at the bottom 131.
The front plate 172 is disposed over the printed-circuit antenna 15 of the exciter 12, and is substantially flush with the aperture 14 and does not protrude. This provision can prevent the onset of surface waves.
There is a wide choice of materials available suitable for the antenna element 10. The waveguide 11 can, for example, be formed from aluminum to provide a lightweight structure, although other metallic, materials, e.g., zinc plated steel, etc. can also be employed.
The shield 17 can, for example, be formed from a hard and strong material to provide good protection from vandalism. Examples of the material suitable for the shield 17 include, but are not limited to, metallic materials.
According to a further embodiment, the antenna element 10 can include a radome 19 mounted on the top of the antenna element over the aperture 14. Placement of a relatively thin radome ensures, inter alia, that the antenna can be waterproof. As will be shown hereinbelow, the thickness of radome affects to a very large extent the resonant frequency of the antenna.
When desired, the space in the cavity 13 between the printed-circuit antenna 15 and the aperture 14 can be filled with a dielectric material.
Exemplary values of design parameters are shown in Table 1.
It should be noted that the geometric parameters of the antenna element are represented within the present description in the dimensions normalized to the value of the wavelength in free space λo. In particular, λo is defined by c/f, where c is the speed of light and f is the frequency of operation of the antenna element.
Referring to
For example, as shown in
In the example shown in
It should still further be noted that the phase array antenna 20 may be used as a single radiator in conjunction with a transceiver device, or it may be combined together with additional antenna arrays to form a larger array antenna. And it should still further be noted that although the front side 22 of the array antenna shown in
Furthermore, this array antenna can include a beam steering system (not shown) coupled to the plurality of the antenna elements 10 and configured for steering an energy beam produced by the phased array antenna. The beam steering system is a known system that can, inter alia, include such components as T/R modules, DSP-driven switches, and other components required to control steerable multi-beams.
It was found that the configuration and parameters of the antenna element 10 and the array antenna structure 20 significantly affect their performance. Several examples of such dependencies will be illustrated herein below.
One of the important parameters of a phased array antenna is spacing S between antenna elements. The spacing S determines the required scan angle of the antenna. Specifically, the farther out the antenna needs to be scanned, the closer the element should be arranged in order to eliminate the onset of grating lobes into real space.
In operation, the spacing S has a major effect on the antenna element (10 in
It should be understood that the spacing S between the elements 10 limits the diameter D of the cavity (13 in
The computer simulations were carried out when the radius R of the cavity was set to 0.200 λo (curve 31), 0.212 λo (curve 32), and 0.217 λo (curve 33), correspondingly. As was noted above, the radius R of the cavity as well as all other geometric parameters of the antenna element are represented herein in the dimensions normalized to the value of the wavelength in free space λo.
As can be seen, the resonant frequency decreases when the radius R of the cavity increases. In practice, the radius of the cavity should be chosen such that the antenna radiates at the desired frequency and bandwidth.
Another parameter of the cavity (13 in
Referring to
The first parameter for which the effect of its magnitude on the frequency response was checked was the thickness l of the front plate 172. Referring to
In practice, the thickness l of the front plate 172 should, inter alia, be chosen to withstand vandalism and other aggressive actions against the antenna. Preferably, the thickness of the front plate is equal to or greater than about 8 mm, in order to properly mechanically protect the antenna element. Accordingly, further computer simulations were carried out in which the front plate was selected in the shape of a disk and the thickness of the front disk was set to 8 mm. For this case, the following parameters were optimized: the radius δ of the holder 171 at the bottom portion 174, the tapering angle α of the holder, the radius r of the front disk and the length s of the cavity (14 in
Referring to
Referring to
Referring to
In practice, the gap should preferably be chosen to be as small as possible. This should be done to make the face of the aperture as smooth as possible, thereby to prevent the antenna from penetrating any foreign objects into the cavity. On the other hand, the gap is the area from which the antenna radiates. Thus, when designing the antenna, one inherently chooses the largest possible gap that is acceptable. The designer then chooses the gap dimension from which the other antenna parameters can be optimized. The inventor believes that in practice, a gap that is suitable can, for example be the gap having dimensions in the range of about 0.0375 λo to 0.0475 λo.
Referring to
The printed-circuit antenna 15 has a layered structure and includes a supporting layer 152 having an underside 153 and an upper side 154. The supporting layer 152 is a thin layer of a dielectric material. As used throughout this description, the terms ‘underside’ and ‘upper side’ are referred to surfaces of the plates and layers in relation to the cavity of the waveguide (10 in
The printed-circuit antenna 15 also includes a patch 151.
Referring back to
According to an embodiment, the patch 151, the supporting layer 152 and the substrate 155 are all have ring shapes hollowed out in the ring center. As shown in
It should be appreciated that from an electromagnetic standpoint it is permitted to place the holder 171 within the center of the patch 151 since the voltage is zero at the center and as the current travels along one direction the voltage is positive, and while the current travels in the opposite direction the voltage is negative. As a result, placing a metallic object in the center of patch symmetric about its center does not disable the patch and does not prevent it from operating properly. The only effect of placing a metallic object is that the resonant frequency is altered.
It was found that the dielectric constant of the substrate can affect the bandwidth and resonant frequency of the antenna element. Accordingly, the dielectric constant of the substrate 155 arranged beneath the patch 151 must be chosen to optimize the performance of the antenna. One must be judicious in choosing the dielectric constant. Choosing a very high dielectric constant might reduce the bandwidth, however choosing a very low dielectric constant might make the exciter too large and unable to fit into the cavity.
An example of the dielectric material suitable for the substrate 155 includes, but is not limited to, ROHACELL® foam which can, for example, be produced by thermal expansion of a co-polymer sheet of methacrylic acid and methacrylonitrile. It should be noted that ROHACELL® foam is formed of a dielectric material having a dielectric constant nearly equivalent to the dielectric constant of air.
Referring to
Referring to
The thickness of the supporting layer 152 should be as thin as possible. The reason for this is in order for the pad 158 and the stub 159 to be as close to the printed circuit patch 151 as possible, since the patch acts as a ground plane for the stub and the pad.
An example of the dielectric material suitable for the supporting layer 152 includes, but is not limited to epoxy glass, however other dielectric materials can also be suitable. The substrate 155 can, for example, be made of a dielectric material, however other materials, e.g., semiconducting ceramics, could also be used for substrate. It was found that the dielectric constant of the PC Board is of minor significance. Since the antenna is very thin, the dielectric constant of the PC Board is not a significant parameter. More important, are the mechanical characteristics of the material. Moreover, one needs a material which can be bonded onto the substrate 155.
Turning back to
The electrically conductive pin 163 passes through a common hole 164 arranged within the waveguide 11 at the bottom of the cavity 13, the sleeve 162 and the supporting layer 152. The pin 163 is connected to the pad 158 at the feed point 161 of the printed-circuit antenna 15. The connection of the pin 163 to the pad 158 can, for example, be carried out by soldering, welding, or by any other suitable technique. According to one embodiment, the pin 163 is surrounded with an isolator layer 165 made, for example, from teflon.
The pin 163 is coupled electromagnetically to the printed circuit patch 151. The pad 158 acts a capacitor in series with the pin 163. The pad 158 and the stub 159 together act as a reactive transmission line in which the patch 151 acts as its ground plane. The purpose of the stub 159 is to tune the patch 151 to 50 ohms or to any other impedance desired. The stub 159 can also increase the bandwidth of the antenna element.
It should be appreciated that the antenna element described above has the ability to operate in any polarization chosen. This implies that the antenna element can provide vertical, horizontal or circular polarized radiation. When desired, the radiation can be polarized to 45 degrees or any other polarization desired. The reason is that the polarization is determined by the position of the feed point 161 with respect to the printed circuit patch 151. Since the patch 151 is symmetric the feed point 161 can be located in any position desired. If circular polarization is desired, two feed points and, correspondingly, two coaxial feed arrangements can be used placed orthogonally to each other and phased 90° apart to achieve circular polarization.
As discussed above, the configuration and parameters of the antenna element and the array antenna structure significantly affect their performance. Several examples of the dependencies of the geometric dimensions of the waveguide (11 in
As one can see, the resonant frequency varies with outer radius of the patch 151. As one can see, the resonant frequency decreases with decrease in the patch radius. It was found by the applicant that the behavior of the resonant frequency of the antenna element, in which the patch is enclosed within a cavity, differs from the behavior of a conventional patch, in which the resonant frequency usually increases with decrease in the patch radius.
The next parameter analyzed was the inner radius rinner of the printed circuit patch (151 in
The next parameter analyzed was the thickness s of the substrate (155 in
As one can see, the thickness of the substrate has a direct effect on the bandwidth and resonant frequency of the antenna. For example, in order that an antenna properly operate between 0.975 fo and 1.02 fo (where fo=c/λo, and c is the light velocity), one can choose a thickness of 0.065 λo.
As described above with reference to
As one can see from
The next parameter analyzed was the radius Rpad of the pad 158. Simulations were done to determine the effect of modifying the radius of the pad.
The further analyzed parameters are the length Lstub and the width Wstub of the stub 159 when the stub has a rectangular shape (as shown in
As can be seen from
It was also found that the distance of the feed point 161 from the center O of the patch 151 has a very noticeable effect on the impedance of the patch 151.
As can be seen from
Turning back to
As one can see from
Turning back to
As such, those skilled in the art to which the present invention pertains, can appreciate that while the present invention has been described in terms of preferred embodiments, the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures systems and processes for carrying out the several purposes of the present invention.
The antenna of the present invention may be utilized in various intersystems, e.g., in communication within the computer wireless LAN (Local Area Network), PCN (Personal Communication Network) and ISM (Industrial, Scientific, Medical Network) systems.
The antenna may also be utilized in communications between a LAN and cellular phone network, GPS (Global Positioning System) or GSM (Global System for Mobile communication).
It is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims. Other combinations and sub-combinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to different combinations or directed to the same combinations, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the present description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201812 | Oct 2009 | IL | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2010/000829 | 10/12/2010 | WO | 00 | 8/17/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/051931 | 5/5/2011 | WO | A |
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| Number | Date | Country |
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| 1 076 379 | Feb 2001 | EP |
| Entry |
|---|
| Gonzalez De Aza et al., “Broad-Band Cavity-Backed and Capacitively Probe-Fed Microstrip Patch Arrays,” IEEE Transactions on Antennas and Propagation, May 2000, pp. 784-789, vol. 48, No. 5, IEEE. |
| May 24, 2013 Office Action issued in European Patent Application. No. 10 773 408.9. |
| Number | Date | Country | |
|---|---|---|---|
| 20120306710 A1 | Dec 2012 | US |
