Abstract:
Antennas and methods of forming the antennas having a very low profile and a built in ground plane are described. The antenna elements are formed of conducting material on a layer of dielectric material, such as an integrated circuit board. The antenna elements are mounted on a ground plane having a number of shorting elements between one of the antenna elements and the ground plane. In some embodiments the antenna elements are on a single side of the layer of dielectric material. In other embodiments the antenna elements are formed on both the top and bottom surfaces of the layer of dielectric material. The self contained ground plane makes the antenna performance independent of proximity to conducting or non conducting surfaces.

Description:
This Patent Application claims priority to the following U.S. Provisional Patent Application, herein incorporated by reference: 
     Ser. No. 60/324,416, filed Sep. 24, 2001 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to low profile antennas having a built-in ground plane which provide good performance in close proximity to either a conducting or a non-conducting surface. 
     (2) Description of the Related Art 
     Antennas are an essential part of electronic communication systems that contain wireless links. Antenna performance is often adversely influenced by close proximity to conducting surfaces. Antennas which provide good performance in close proximity to either a conducting or a non-conducting surface offer significant advantages for these systems. 
     U.S. Pat. No. 5,371,507 to Kuroda et al. describes a planar antenna comprising a ground conductor, a dielectric layer laminated on the ground conductor, and a radiation element laminated on the dielectric layer. 
     U.S. Pat. No. 5,703,600 to Burrell et al. describes a microstrip antenna comprising a planar antenna radiating element, a ground plane, and a dielectric material placed between the radiating antenna element and the ground plane. 
     U.S. Pat. No. 6,355,703 to Chang et al. describes a microstrip patch antenna with enhanced beamwidth characteristics. The antenna comprises a patch element and a ground plane separated from the patch element by a first dielectric layer. 
     U.S. Pat. No. 4,779,097 to Morchin describes a segmented phased array antenna system for scanning two different ranges of directions with a single set of antenna elements. 
     SUMMARY OF THE INVENTION 
     Antennas are an essential part of electronic systems that contain wireless links. The performance of antennas is frequently affected by the environment in which they operate such as close proximity to conductors or conducting surfaces. Environmental degradation of performance is a significant disadvantages for antennas. 
     It is a principal objective of this invention to provide an antenna having antenna elements formed on a single side of a layer of dielectric material which has excellent performance in close proximity to either a conducting or a non-conducting surface. 
     It is another principal objective of this invention to provide an antenna having antenna elements formed on both the top surface and the bottom surface of a layer of dielectric material which has excellent performance in close proximity to either a conducting or a non-conducting surface. 
     It is another principal objective of this invention to provide a method of forming an antenna having antenna elements formed on a single side of a layer of dielectric material which has excellent performance in close proximity to either a conducting or a non-conducting surface. 
     It is another principal objective of this invention to provide a method of forming an antenna having antenna elements formed on both the top surface and the bottom surface of a layer of dielectric material which has excellent performance in close proximity to either a conducting or a non-conducting surface. 
     These objectives are achieved with a very low profile antenna that has a built-in ground plane. The antenna elements are formed by etching conducting material formed on an insulating material, such as an integrated circuit board. One set of implementations requires an insulating board with one side having a conducting material. Another set of implementations requires an insulating board with both sides having conducting materials. The antenna elements are mounted on a ground plane having a number of shorting elements between one of the antenna elements and the ground plane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A shows a top view of the active part of an antenna of this invention using conducting material on a single side of an insulator board. 
     FIG. 1B shows a cross section view of the active part of the antenna shown in FIG. 1A, taken along line  1 B- 1 B′ of FIG.  1 A. 
     FIG. 2A shows a top view of an antenna of this invention using the active antenna part of the antenna shown in FIGS. 1A and 1B. 
     FIG. 2B shows a cross section view of the antenna of FIG. 2A taken along line  2 B- 2 B′ of FIG.  2 A. 
     FIG. 2C shows a perspective view of the antenna shown in FIGS. 2A and 2B. 
     FIG. 3A shows a top view of a ground plane of this invention after shorting elements and standoff members have been delineated in the ground plane material. 
     FIG. 3B shows a top view of the ground plane of FIG. 3A after the shorting elements and standoff members have been bent at 90° from the ground plane. 
     FIG. 3C shows a cross section view of the ground plane of FIG. 3B taken along line  3 C- 3 C′ in FIG.  3 B. 
     FIG. 4 shows a cross section view of part of the ground plane of FIGS. 3A-3C and part of the active part of an antenna showing electrical contact between the ground place and active part of the antenna and a mechanical standoff with insulation between the ground plane and the active part of the antenna. 
     FIG. 5A shows a top view of a second antenna of this invention using conducting material on a single side of an insulator board. 
     FIG. 5B shows a cross section view of the antenna of FIG. 5A taken along line  5 B- 5 B′ of FIG.  5 A. 
     FIG. 6A shows a top view of a third antenna of this invention using conducting material on a single side of an insulator board. 
     FIG. 6B shows a cross section view of the antenna of FIG. 6A taken along line  6 B- 6 B′ of FIG.  6 A. 
     FIG. 7A shows a top view of an antenna of this invention using conducting material on a two sides of an insulator board. 
     FIG. 7B shows a cross section view of the antenna of FIG. 7A taken along line  7 B- 7 B′ of FIG.  7 A. 
     FIG. 7C shows a cross section view of the antenna of FIG. 7A taken along line  7 C- 7 C′ of FIG.  7 A. 
     FIG. 7D shows the bottom view of the antenna of FIG. 7A without the ground plane, coaxial cable, insulating standoffs, or electrical connections between the ground plane and active part of the antenna. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to FIGS. 1A to  6 B for a description of the preferred embodiments of this invention for antennas using a layer of dielectric material, such as an insulator board, having conductor material on a single side of the layer of dielectric material for the active part of the antenna. FIG. 1A shows a top view and FIG. 1B a cross section view of the active part of an antenna of this invention. The cross section shown in FIG. 1B is taken along line  1 B- 1 B′ of FIG.  1 A. The active part of the antenna comprises a first antenna element  14  and a second antenna element  12  formed of conducting material. The first antenna element  14  and the second antenna element  12  comprise conducting material; such as aluminum, copper, or the like; formed on a layer of dielectric material  11 . An insulating gap  16  separates the first antenna element  14  from the second antenna element  12 . First shorting elements  15  form electrical connections between the first antenna element  14  and the second antenna element  12 . In this example there are two first shorting elements  15 . The two first shorting elements are narrow in width with locations affecting the optimum resonance frequency of the antenna as well as the impedance of the antenna resonance. In effect the two shorting elements  15  affect the inductance and capacitance of the active part of the antenna. 
     The length of the outer perimeter of the first antenna element  14  is a first distance and the length of the outer perimeter of the second antenna element  12  is a second distance. In this example the first antenna element  14  is a rectangle having a length  17  and a width  19 . To realize resonance at the desired frequency, the perimeter of the first antenna element  14  (twice the length  17  plus twice the width  19 ) must be equal to a multiple of one quarter of the wavelength of the desired frequency. The length  17  and width  19  of the first antenna element  14  can vary, but as long as the perimeter, twice the length  17  plus twice the width  19 , is a multiple of one quarter of the wavelength of the desired frequency the antenna will resonate at the desired frequency. In order to realize optimum performance of the antenna at the desired frequency, the outer perimeter of the second antenna element  12  must also be equal to a multiple of a quarter wavelength of the desired frequency. The active part of the antenna  10  is typically formed by etching a pattern in a layer of conducting material formed on a layer of dielectric material  11 . A gap  16  of a third distance  18  separates the first antenna element from the second antenna element  12 . In this example the third distance  18  is typically about 0.5 inches, however other values of the third distance  18 , larger or smaller, are possible and can be used. 
     In the completed antenna the active part of the antenna  10  is positioned over a ground plane. FIG. 2A shows a top view and  2 B shows a cross section view of the completed antenna with the active part of the antenna  10  positioned over the ground plane  80 . FIG. 2B shows a cross section of the antenna shown in FIG. 2A taken along line  2 B- 2 B′ of FIG.  2 A. The first antenna element  14  and the second antenna element  12  lie in a single plane which is parallel to the ground plane  80 . The plane having the first antenna element  14  and the second antenna element  12  is a fourth distance  21  from the ground plane. The fourth distance  21  is between about 0.1 and 0.25 inches in a typical implementation, however the fourth distance  21  may vary, larger or smaller, for optimum performance at a given frequency. A number of second shorting elements  24  form electrical connections between the second antenna element  12  and the ground plane  80 . As shown in FIG. 2A the second shorting elements  24  can be located either on the outer periphery or the interior of the second antenna element  12 . The purpose of these shorting elements is to modify the capacitance and inductance of the active part of the antenna and thereby optimize the antenna impedance at the resonance frequency. In most cases the goal of this optimization is to realize an antenna impedance of 50 ohms. 
     A perspective view of the antenna is shown in FIG.  2 C. As shown in FIG. 2C electrical connection is made to the first antenna element  14  using a coaxial cable  26  having an outer shield, hidden from view in FIG.  2 C and an center conductor  30 . The coaxial cable  26  is routed between the active part of the antenna  10  and the ground plane  80  with the center conductor  30  passing through a hole  28  in the first antenna element  14  and electrically connected to the top surface of the first antenna element  14 . The outer shield of the coaxial cable  26  is connected to the ground plane  80 . 
     The antenna of this invention is very compact and has its own ground plane so that the antenna performance is not affected by proximity to either conducting or non conducting surfaces. The antenna of this embodiment is currently used for frequencies from about 100 megahertz (MHz) to about 3 gigahertz (GHz), but the same design concept can be used for frequencies as low as 3 kilohertz (KHz) and frequencies as high as 100 GHz. Specific product designs of this invention have been used at frequencies of 400 MHz, 850 MHz, 1500 MHz, 1900 MHz, and 2400 MHz. 
     FIGS. 3A,  3 B,  3 C, and  4  show an example of a method of forming the second shorting elements and mechanical standoffs holding the active part of the antenna in position relative to the ground plane. In this method, as shown in FIG. 3A, gaps  34  are cut in the ground plane  80  of form second shorting elements  36  and standoffs  38 . As shown in FIGS. 3B and 3C the second shorting elements  36  and standoffs  38  are then bent at 90° to the ground plane  80 . FIG. 3B shows a top view and FIG. 3C a side view, taken along line  3 C- 3 C′ of FIG. 3B, of the ground plane  80  after the second shorting elements  36  and standoffs  38  have been separated from the ground plane  80  and bent at 90°. FIG. 4 shows one of the second shorting elements  36  in position to be electrically connected to the second antenna element  12  and one of the standoffs  38  in contact with the dielectric layer  11 . 
     Other shapes can also be used for the first antenna element in this embodiment for frequencies between about 3 KHz and 30 GHz. FIGS. 5A shows a top view and  5 B a cross section view, taken along line  5 B- 5 B′ of FIG. 5A, of an antenna having a rectangular first antenna element  54  with any ratio of the length  57  to width  59  which is practical to implement as long as the perimeter, twice the length  57  plus twice the width  59 , is a quarter multiple of a quarter wavelength of the desired resonance frequency of the antenna. Also the outer perimeter of the second antenna element  52  must be equal to a multiple of a quarter wavelength of the desired resonance frequency for optimum antenna performance. 
     Also, as previously described, the impedance of the antenna is tuned by the number and location of the second shorting elements  24 , and connections to the antenna are made using a coaxial cable routed and connected as previously described. 
     FIG. 6A shows a top view and  6 B a cross section view, taken along line  6 B- 6 B′ of FIG. 6A, of an antenna having a circular first antenna element  64 . The length of the outer perimeter of the first antenna element  64  is the first distance. The length of the outer perimeter of the second antenna element  62  is the second distance. As previously described a gap  66  separates the first antenna element  64  from the second antenna element  62 , first shorting elements  65  connect the first antenna element  64  and second antenna element  62 , and second shorting elements  24  connect the second antenna element  62  to the ground plane  80 . The first antenna element  64  and second antenna element  62  are co-planar and formed on a layer of dielectric  61 . The first antenna element  64  and second antenna element  62  are the fourth distance  21  from the ground plane. 
     As previously described the first distance and second distance are integral multiples of a quarter wavelength, the impedance of the antenna is tuned by the number and location of the second shorting elements  24 , and connections to the antenna are made using a coaxial cable routed and connected as previously described. 
     Although the spacing between the active part of the antenna and the ground plane has been shown as an air gap in these embodiments, other dielectric materials can be used. Any dielectric material having low dielectric losses at the frequencies of operation can be used. In these embodiments the first and second antenna elements are formed on a layer of dielectric material. One example of such a dielectric material is circuit board material, which provides low cost implementation in the range of frequencies from about 100 MHz to 5 GHz. At frequencies in the gigahertz range ceramic dielectric material can be used and multilayer ceramic can be used to provide both the dielectric layer and conducting layers. A frequencies where one quarter of a wavelength are in the millimeter range the antennas can be implemented in the wiring layers of an integrated circuit. 
     Refer now to FIGS. 7A to  7 D for a description of the preferred embodiment for antennas of this invention using a layer of dielectric material, such as insulator board, with conducting material on both the top surface and the bottom surface of the layer of dielectric material to form the active part of the antenna. As in the previous embodiment, the active part of the antenna  70  is positioned above a ground plane  80 . The top view of the active part of the antenna  70  can be seen in FIG.  7 A and the bottom view of the active part of the antenna  70  is shown in FIG.  7 D. FIG. 7B shows a cross section view of the antenna taken along line  7 B- 7 B′, and FIG. 7C shows a cross section view of the antenna taken along line  7 C- 7 C′. 
     In this embodiment the first antenna element  74  is formed on the bottom surface of a layer of dielectric material  71  and the second antenna element  72  is formed on the top surface of the layer of dielectric material  71 . In FIG. 7A the outline of the outer perimeter of the first antenna element is shown by a dashed line  75 . In FIG. 7C the outline of the inner perimeter of the second antenna element is shown by a dashed line  77 . As can be seen in FIGS. 7A,  7 B, and  7 D the outer perimeter of the first antenna element  74  overlaps the inner perimeter of the second antenna element  72 . As can be seen in FIGS. 7A and 7B a first electrical connection  94  connects the center conductor  93  of a coaxial cable  90  to the first antenna element  74  and a second electrical connection  92  connects the shield  91  of the coaxial cable to the ground plane  80 . FIGS. 7A and 7B show that the coaxial cable and connections are located at one end of the first antenna element  74 . The location of the first electrical connection  94 , connecting the center conductor  93  of a coaxial cable  90  to the first antenna element  74 , relative to the first antenna element  74  is shown by a dashed circle in FIG. 7A and a solid dot in FIG.  7 B. 
     As shown in FIGS. 7A and 7C there are a number of second shorting elements  24  connecting the second antenna element  72  to the ground plane  80 . In this example two second shorting elements  24  are shown but more or fewer can be used. Also shown in FIGS. 7A and 7C there are a number of insulating standoff elements  85  holding the active part of the antenna  70  is position relative to the ground plane  80  and maintaining a fourth distance  82  between the bottom of the layer of insulating material and the top of the ground plane  80 . In this example thirteen insulating standoff elements  85  are shown but more or fewer can be used. 
     The capacitive coupling between the first antenna element  74  and the second antenna element  72 , due to the overlap between the outer perimeter of the first antenna element  74  and the inner perimeter of the second antenna element  72 , provides the electrical coupling necessary between the first antenna element  74  and the second antenna element  72 . In this embodiment two second shorting elements  24  are used to provide electrical connection between the second antenna element  72  and the ground plane  80 , however more or fewer second shorting elements  24  could be used. The capacitance of the overlap regions and the inductance modifications of the second shorting elements  24  optimize the antenna impedance at the resonance frequency. In most cases the goal of this optimization is to realize an antenna impedance of 50 ohms. The bottom of the layer of dielectric material  71  is a fourth distance  82  from the ground plane  80 , see FIG.  2 B. The fourth distance  82  is generally between about 0.1 and 0.5 inches, however the fourth distance  82  may vary, larger or smaller, for optimum performance at a given frequency. 
     As in the preceding embodiment, the length of the outer perimeter of the first antenna element  74 , the first distance, is equal to an integral multiple of a quarter wavelength of the resonance frequency of the antenna. The length of the outer perimeter of the second antenna element  72 , the second distance, is also equal to an integral multiple of a quarter wavelength of the resonance frequency of the antenna. The impedance of the antenna is tuned by the location of the two second shorting elements  24 . Electrical connection to the antenna of this embodiment is made using a coaxial cable routed between the active part of the antenna  70  and the ground plane  80  with the center conductor electrically connected to the first antenna element  74  and the outer shield of the coaxial cable connected to the ground plane  80 . The location and detail of the coaxial cable connections are shown in FIGS. 7A and 7B. 
     The antenna of this embodiment of the invention also has its own ground plane so that the antenna performance is not affected by proximity to either conducting or non conducting surfaces. The antenna of this embodiment is generally used for frequencies from about 100 MHz to about 5 GHz, but can also be scaled to be used at frequencies from 3 KHz to 100 GHz. 
     Although the spacing between the active part of the antenna and the ground plane has been shown as an air gap in these embodiments, other dielectric materials can be used. Any dielectric material having low dielectric losses at the frequencies of operation can be used. In these embodiments the first and second antenna elements are formed on a layer of dielectric material. One example of such a dielectric material is circuit board material, which provides low cost implementation in the range of frequencies from about 100 MHz to 5 GHz. At frequencies in the gigahertz range ceramic dielectric material can be used and multilayer ceramic can be used to provide both the dielectric layer and conducting layers. A frequencies where one quarter of a wavelength are in the millimeter range the antennas can be implemented in the wiring layers of an integrated circuit. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.