Abstract:
A microstrip antenna includes a ground plane element and a radiating element. An elongated trough is formed generally in the middle of the radiating element so as to divide the radiating element into two generally equally-sized portions, and in a manner to extend outward from a bottom surface of the radiating element. The trough includes a first side edge, a second side edge, and a bottom surface. A first radiating portion extends from the first side edge, and a second radiating portion extends from the second side edge. The trough provides an elongated microstrip-size element at the bottom surface of the trough. A relatively thin dielectric layer is provided between the bottom surface of the trough and a corresponding portion of the ground plane element, thereby providing that a microstrip transmission line is formed by the bottom surface of the trough, the thin dielectric layer, and the corresponding portion of the ground plane element. A first feed conductor is connected to the ground plane element, and a second feed conductor is connected to the bottom of the trough.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     U.S. Pat. No. 5,734,350, issued Mar. 31, 1998, entitled MICROSTRIP WIDE BAND ANTENNA, is incorporated herein by reference. 
     U.S. patent application Ser. No. 09/155,831, filed Oct. 6, 1998 entitled MICROSTRIP WIDE BAND ANTENNA AND RADOME, is incorporated herein by reference. 
     U.S. Patent application Ser. No. 09/441,529, filed Nov. 16, 1999, entitled WIDE BAND ANTENNA HAVING UNITARY RADIATOR/GROUND PLANE, is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of microstrip antennas. More specifically, this invention relates to a microstrip antenna having a microstrip feed line trough that is integrally formed in the antenna&#39;s radiating element. 
     2. Description of the Related Art 
     The art provides small patch and microstrip antennas that are generally useful for their limited intended purposes. However, the need remains in the art for a patch antenna that is of simple construction and that provides wide bandwidth operation. 
     As a feature of the present invention, an antenna having a two-section radiating element is provided, the radiating element having a microstrip feedline trough formed therein. 
     Uniform rectangular guides having a centered rectangular ridge on one, or both, of its wide sides is known. For example, see the publication WAVEGUIDE HANDBOOK by N. Marcuvitz, 1986, published by Peter Peregrinus Ltd., London, UK. 
     SUMMARY OF THE INVENTION 
     This invention provides a new and unusual form of a patch antenna having a wide bandwidth when the antenna is compared to existing patch antennas of a similar physical size. Antennas in accordance with the present invention are of relatively simple construction, and include a microstrip trough structure that is formed within a metal-radiating patch element. In preferred embodiments, the microstrip trough is formed generally in the center of the radiating element so as to divide the radiating element into two generally identical radiating portions. 
     The bottom of the trough is positioned closely adjacent to a metal ground plane element, to thereby form a pseudo microstrip transmission line by which a feed input is applied to the antenna&#39;s two-portion radiating element. A first input feed probe, or a first input feed conductor, is electrically connected to the bottom of the trough, and a second input feed conductor is electrically connected to the ground plane element. For example, the center conductor of a coaxial cable transmission line is connected to the bottom of the trough, and the metal sheath of the coaxial cable is connected to the ground plane element. 
     In accordance with an embodiment of the invention, a folded or bent radiating element is provided whereby a narrow, linear, elongated, and generally U-shaped cross-section trough is formed by bending, or forming, a rectangular shaped metal (copper) radiating patch generally in its mid-portion, thus providing a first radiating element portion on one side of the trough, and a second radiating element portion on the other side of the trough. In a non-limiting embodiment of the invention, the two radiating element portions are of the same physical shape and size. For example, the two radiating element portions are rectangular or square in shape. 
     The bottom of the U-shaped trough is located closely adjacent and generally parallel to a metal (copper) ground plane element that underlies the two radiating element portions. The bottom of the trough operates as the antenna&#39;s relatively low impedance (50 ohm) microstrip feed line. Since the bottom of the trough is substantially closer to the ground plane element than are the two portions of the radiating element, a shorter feed probe than is traditionally used can be provided to electrically connect to the trough and then to the two radiating elements. This shortness property of the probe operates to control the impedance of the probe in order to provide a good impedance match between the antenna and its feed line. More specifically, this construction and arrangement operates to lower the inductance that is required for a good impedance match, thus allowing the use of existing and well-known commercially-available probe terminating connectors to provide for input feed to the antenna, rather than requiring the use of more complicated structures that are sometimes used to achieve a broad bandwidth patch antenna. 
     In accordance with a feature of the invention, an input feed network is provided comprising a probe feed, or an edge feed, into the metal microstrip line that includes the bottom of the above-described trough. This microstrip line or trough is integral with the two-portion radiating patch element, and this microstrip line is physically sized in width to be of a desired impedance; for example, 50 ohms. This construction and arrangement of the invention provides an efficient electrical transition from a transmission line, such as a coaxial cable into the antenna, further resulting in a structure that provides a broadband characteristic to the antenna as a whole, in particular to the primary resonant mode in which the antenna operates as a one-half wavelength patch antenna, resulting in a directional radiation pattern over a wide range of frequencies. 
     Antennas in accordance with the present invention operate in multiple resonant modes within the same physical antenna structure, with a smooth transition being provided between the various resonant modes, where the various modes comprise regions of radiation in particular patterns. The presence of these multiple modes give rise to an overall bandwidth of 50-percent or more, all of the modes being effectively impedance matched by the impedance matching trough construction and arrangement above described. As a result, antennas in accordance with the invention are impedance matched across an extremely large frequency range as compared to known patch antennas of similar physical size. Stated another way, antennas in accordance with the invention, exhibit multiple resonances, all of which are impedance matched to the input feed line. 
     These and other features and advantages of the present invention will be apparent to those of skill in the art upon reference to the following detailed description, which description makes reference to the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective top/front view of a first embodiment of a broadband microstrip patch antenna in accordance with the invention. 
     FIG. 2 is a front view of the FIG. 1 embodiment, this figure showing two of the four dielectric space adjustment posts, or bolts, that physically support the antenna generally planar and trough-type metal radiating element above the antenna generally planar metal ground plane element, and this figure showing the generally U-shaped cross section of a pseudo microstrip transmission line that includes the bottom wall of the trough that is formed in the radiating element. 
     FIG. 3 is a top view of the FIG. 1 embodiment. 
     FIG. 4 is a front-side view of a second embodiment of a broadband microstrip patch antenna/radome assembly in accordance with the invention, the base and cover of the radome being shown in section in order to expose a patch antenna of the type above described relative to FIGS. 1-3. 
     FIG. 5 is a side view of the antenna/radome assembly of FIG. 4 wherein the base and cover of the radome is again shown in section. 
     FIG. 6 is a top view of the ground plane element of the antenna of FIG.  4 . 
     FIG. 7 is a top view of the radiating element of the antenna of FIG.  4 . 
     FIG. 8 is an enlarged view of the end of the microstrip trough that is formed in the FIG. 7 radiating element. 
     FIG. 9 is an enlarged view of the soldering area that is provided in the microstrip trough of the FIG. 7 radiating element. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a top and front-side perspective view of a first embodiment of a broadband antenna  10  in accordance with the invention, antenna  10  having a three-member composite radiating element  12  that is made of two radiating element portions  29 ,  30 , and a centrally-located pseudo microstrip feed line trough  19  having generally a U-shaped cross section. 
     FIG. 2 is a front-side view of antenna  10 . FIG. 2 shows two of the four dielectric support and/or adjustment posts or bolts  11  that physically support the antenna trough-type metal radiating element  12  above the antenna metal ground plane element  13 . FIG. 2 also shows an electrical connector  14  of the coaxial cable type, the outer metal housing  15  of connector  14  being mounted on, and electrically connected to, the bottom surface  16  of ground plane element  13  , and the centrally located metal conductor or feed probe  17  of connector  14  being electrically connected, or soldered, to the bottom metal surface  18  of trough  19  that is formed in radiating element  12 . 
     While radiating element  12  and ground plane element  13  are specified as being copper members, the spirit and scope of the invention does not require the use to this specific metal. More generally, an electrically conductive metal or a metal-clad composite material that is thick enough to be generally self-supporting is all that is required. For example, it may be desirable for purposes such as lower cost to use a dielectric substrate that is copper-clad on one, or both, sides thereof. 
     FIG. 3 is a top view of antenna  10 , this figure showing all four of the dielectric posts  11  that physically space/support radiating element  12  and ground plane element  13  relative to each other. In a non-limiting embodiment of the invention, each of the four posts  11  was located, or spaced, generally 0.3-inch from the adjacent corner of radiating element  12 , as shown by dimensions  21  in FIG.  3 . 
     While in a preferred embodiment, radiating element  12  was generally centered over ground plane element  13 , as is best seen in FIG. 3, the spirit and scope of the invention is not to be limited to this centered arrangement. All that is required is that any given portion of radiating element  12  be provided with a corresponding underlying portion of ground plane element  13 . 
     The FIG. 1-3 embodiment of the invention provides a broadband microstrip patch antenna  10 , wherein the width  20  of the trough  19  that is formed in radiating element  12  is chosen and adjusted to provide a desired microstrip feed line impedance for feeding radiating element  12 ; for example, a 50 ohm input feed line impedance. 
     The frequency mode characteristic or property of antenna  10  is broadband in a manner that is similar to that of a ridged waveguide. The use of an electrically small, or short, length feed probe  17  (for example, about 0.1-inch long) desirably provides a decrease in the feed probe inductance at the higher frequency modes of antenna  10 . The length of feed probe  17  is frequency dependent in that the higher the frequency of operation of antenna  10 , the shorter will be feed probe  17 . 
     In an embodiment of the invention, antenna  10  operated in a broadband frequency range from about 1.50 to about 2.75 GHz, and ground plane element  13  comprised a generally flat or planar copper member that was about 20-mils thick and in the range of from about 4.08 to about 4.75-inch square. Note that the planar shape of ground plane element is not critical to the invention since other shapes can be provided to accomplish the antenna ground plane function. 
     In this embodiment of antenna  10 , the thickness of the air dielectric layer that separated the bottom surface  18  of trough  19  from the top surface  25  of ground plane element  13  was quite thin, and in the range of from about 0.082 to about 0.1-inch, this dimension establishing the length of feed probe  17 . 
     It is to be noted that use of an air dielectric layer is not required by the spirit and scope of the invention. For example, a dielectric plastic material may occupy the space that exists between the bottom surface  18  of trough  19  and the top surface  25  of ground plane element  13 . 
     Radiating element  12  and its trough  19  is also formed of copper that is about 20 mils thick. Trough  19  is made of three structural copper walls, i.e. a narrow bottom wall  26  having a microstrip width  20  in the range of from about 0.481 to about 0.539-inch, and two parallel side walls  27  and  28  that each meet bottom wall  26  at a right angle, i.e. side walls  27  and  28  extend perpendicularly upward from bottom wall  26 . 
     In this embodiment of the invention, radiating element  12  includes two identical size and rectangular-shaped radiating element portions  29  and  30  wherein the long dimension  32  of each rectangle extends parallel to the centrally-located longitudinal axis  22  of trough  19 . In an embodiment of the invention, the planar area or size occupied by composite radiating element  12  comprised a rectangle having a long side  32  that was about 2.68-inch long, and having a short side  33  that was about 2.55-inch long. 
     It is to be noted that within the spirit and scope of the invention, other planar shapes of radiating element portions  29 ,  30  can be provided, including radiating element portions  29 ,  30  that are of different individual physical shapes, and/or of different individual planar areas. 
     Without limitation thereto, radiating element portions  29  and  30  occupy a common flat plane that is generally parallel to a plane that is occupied by ground plane element  13 . The plane that is occupied by radiating element portions  29 ,  30  is spaced from the plane that is occupied by ground plane element  13  by a distance  31  that is in the range of from about 0.430 to about 0.495-inch. 
     In an alternative embodiment, radiating element portions  29 ,  30  can occupy two different individual planes that are each tilted to the plane that is occupied by ground plane element  13 , as is taught by above cited U.S. Pat. No. 5,734,350. 
     In accordance with this invention, the three-member structural combination that comprises (1) the microstrip narrow and planar metal bottom wall  26  of trough  19 , (2) the corresponding thin and microstrip narrow and planar dielectric layer  23  (see FIG. 1) that underlies bottom wall  26 , and (3) the corresponding microstrip narrow and planar underlying metal portion of ground plane element  13 , operates as a pseudo microstrip transmission line that is constructed and arranged to provide impedance matching to an antenna feed line and probe  17  that are connected to connector  14 . For example, 50 ohm impedance matching is provided between antenna  10  and a coaxial feed cable (not shown) that is connected to connector  14 . This three-member microstrip transmission line also operates somewhat like a ridged waveguide. It is to be noted that the thinness parameter of dielectric layer  23  is directly related to the length of feed probe  17 , this thinness parameter operating to control, at least in a major part, the impedance of the three-member microstrip transmission line, and this thinness parameter of dielectric layer  23  also enabling the use of a short-length feed probe  17 , thus contributing to the antenna&#39;s broadband characteristic. 
     While the bottom wall  26  of trough  19  is preferably a planar wall that extends parallel to the plane that is occupied by ground plane element  13 , the spirit and scope of the invention is not to be limited thereto. For example, bottom wall  26  may comprise an outwardly-convex curved surface, and preferably a convex curved surface that is formed about an axis that extends parallel to the plane that is occupied by ground plane element  13 . 
     The physical location whereat feed probe  17  is electrically connected to the bottom wall  26  of trough  19  is not critical to the invention. In an embodiment of the invention, feed probe  17  was centrally-located on the width  20  of trough  19 , and feed probe  17  was located at a distance  24  that was in the range of from about 0.425 to about 0.470-inch from the front edge  34  of trough  19 . It is within the spirit and scope of the invention to provide an edge-type electrical feed connection to radiating element  12  by way of an electrical connection to edge  34 ; for example, by way of a microstrip line (not shown) that connects to edge  34 . 
     While no radome is shown relative to this first embodiment, a radome of the type described in above-mentioned copending patent application Ser. No. 09/155,831 can be used to good advantage. 
     FIG. 4 is a front-side view of a second embodiment of a broadband microstrip patch antenna/radome assembly  40  in accordance with the invention, this assembly including a plastic radome having a base portion  41  and a cover portion  42 . A non-limiting and example size of antenna/radome assembly  40  is about 8.81-inch wide and about 2.22-inch high, as is represented respectively by dimension  43  and  44  in FIG. 4, and about 11.19-inch long, as is represented by dimension  45  in FIG.  5 . 
     In FIGS. 4 and 5, radome  41 ,  42  is shown in section in order to expose a metal and generally planar ground plane element  113  and a metal trough-type radiating element  112 , both of which are constructed and arranged as above-described relative to ground plane element  13  and radiating element  12  shown in FIG.  1 . By way of example only, radome  41 ,  42  may comprise a white, vacuum formed, textured side out, acrylonitrile butadiene styrene copolymer (ABS resin) that is about {fraction (3/32)}-inch thick. 
     FIG. 6 is a top view of the ground plane element  113  that is housed or sealed within radome assembly  41 ,  42 . In this embodiment of the invention, dimension  46  of FIG. 6 was about 10.50-inch, and dimension  47  was about 8.13-inch. In this embodiment of the invention, ground plane element  113  is a rigid dielectric substrate having a thin layer of copper on both sides thereof. 
     The top copper layer  125  (i.e., the copper layer that faces radiating element  112 ) of ground plane element is processed at an annular area  48  having a diameter of about 0.50-inch in order to remove that annular portion of top copper layer  125 , thus exposing dielectric substrate  49 . A through hole  50  of about 0.10-inch diameter is formed through ground plane element  113 . Through hole  50  provides for the passage of an electrical feed conductor that electrically connects to the bottom surface  126  of the trough  119  that is formed in radiating element  112 , as above described relative to the FIG. 1-3 embodiment of the invention (in this case, by way of a simple and inexpensive soldering operation). 
     In order to aid in the support of radiating element  112  at the soldering portion thereof, a hollow brass tube  117 , having an length of about 0.50-inch and having an outer diameter of about 0.094-inch, is provided. The annular bottom surface of brass tube  117  physically engages dielectric substrate area  49 , and is thus electrically insulated from top copper surface  125 , whereas the top annular surface of brass tube  117  physically engages and electrically connects to the bottom surface  126  of metal trough  119  that is formed in radiation element  112 . 
     FIG. 7 is a top view of the trough-type radiating element  112  of antenna/radome assembly  40 , and FIG. 8 is an enlarge view of the front side of the copper trough  119  that is formed by walls  126 ,  127 ,  128  that are formed in radiating element  112 . In this embodiment of the invention, the dimension  52  of radiating element  112  that extends generally perpendicular to the axis  122  of trough  119  was about 7.00-inch, whereas dimension  53  that extends generally parallel to the axis  122  of trough  119  was about 6.22-inch. Again, radiating element  112  was generally centered over ground plane element  113 , as best seen in FIGS. 4 and 5. 
     In this embodiment of the invention, the microstrip width  120  of trough  119  was about 1.250-inch, and the height  51  of the two side walls  127 ,  128  was about 0.920-inch. Again, the width parameter of trough  119  is selected to provide impedance matching to the antenna feed means. 
     FIG. 9 is an enlarged view of a soldering area  200  that is provided in the bottom wall  126  of the trough  119  of radiating element  112 . As is taught by above-cited copending patent application Ser. No. 09/441,529, soldering area  200  includes a pair of parallel and generally equal size through slots  201  and  202  that thermally isolate the metal (copper) area  203  that exists between the two slots  201 ,  202 . A small through hole  205  is provided in bottom wall  126  of trough  119 . A feedline metal electrical conductor (not shown in FIG. 9) extends upward through hole  205 , and this conductor is soldered to the top surface of bottom wall  126 . The thermal isolation that is provided by slots  202 ,  203  is such that the heat sink characteristic of solder area  203  is considerably reduced, and as a result, simple and low cost soldering procedures can be used to solder thin conductor to the top surface of bottom wall  126 . As is taught by this copending patent application, slots  202 ,  203  preferably extend parallel to the direction in which current flows in bottom wall  126  of trough  119 . In this embodiment of the invention, through slots  202 ,  203  were about 0.5-inch long and about 0.045-inch wide, and slots  202 ,  203  were spaced from each other by about 0.25-inch, to thus provide a rectangular-shaped soldering area  203  that measured about 0.5×0.25-inch. 
     The invention has been described while making detailed reference to preferred embodiments thereof. However, since it is known that others skilled in the art will, upon learning of the invention, readily visualize yet other embodiments that are within the spirit and scope of the invention, this detailed description is not to be taken as a limitation on the spirit and scope of the invention.