Abstract:
A multi-segmented planar antenna with a built in ground plane and method of forming the antenna are described. The antenna elements are formed on a layer of first dielectric having conducting material on both the first and second sides of the layer of first dielectric, such as a printed circuit board. Antenna elements are formed on both sides of the layer of first dielectric using selective etching of the conducting material. Two antenna elements are generally rectangular separated by a narrow gap and electrically connected by two shorting strips across the gap. Two antenna elements are long and narrow wherein the length of each is an integral multiple of a quarter wavelength of the operating frequencies of the antenna. A layer of second dielectric is placed between the layer of first dielectric having the antenna elements and a ground plane. The antenna can be fully encapsulated in a plastic encapsulation material.

Description:
[0001]    This application claims priority to U.S. Provisional Patent Application serial No. 60/392,858, filed Jul. 1, 2002 which is herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    (1) Field of the Invention  
           [0003]    This invention relates to a planar antenna having a built in ground plane, a low profile, and small area which has excellent performance in close proximity to either a conducting or non conducting surface.  
           [0004]    (2) Description of the Related Art  
           [0005]    A number of workers have disclosed planar type antennas.  
           [0006]    U.S. Pat. No. 6,329,950 B1 describes a planar antenna having two joined conducting regions connected to a coaxial cable.  
           [0007]    U.S. Pat. No. 4,410,891 to Schaubert et al. describes a microstrip antenna the polarization of which can easily be changed.  
           [0008]    U.S. Pat. No. 6,097,345 to Walton describes a dual band slot antenna for cellular telephone and global positioning system frequency bands.  
           [0009]    U.S. Pat. No. 6,429,828 B1 to Tinaphong et al. describes a VHF/UHF self-tuning planar antenna system.  
         SUMMARY OF THE INVENTION  
         [0010]    Antennas are essential in any electronic systems containing wireless links. Such applications as communications and navigation require reliable sensitive antennas. It is very desirable if these antennas are compact, stable, and are not affected by the proximity of either conductive or non conductive surfaces.  
           [0011]    In is a principle objective of this invention to provide a very low profile, small area antenna that has excellent performance in close proximity to either conducting or non conductive surfaces.  
           [0012]    In is another principle objective of this invention to provide a method of forming very low profile, small area antenna that has excellent performance in close proximity to either conducting or non conductive surfaces.  
           [0013]    These objectives are achieved using a multi-segmented planar antenna with a built in ground plane. The antenna elements are formed on a layer of first dielectric having conducting material on both the first and second sides of the layer of first dielectric, such as a printed circuit board. First and second antenna elements are formed on the first side of the layer of first dielectric using selective etching of the conducting material on the first side of the layer of dielectric. Third and fourth antenna elements are formed on the second side of the layer of first dielectric using selective etching of the conducting material on the second side of the layer of dielectric.  
           [0014]    The first and second antenna elements are generally rectangular separated by a narrow gap and electrically connected by two shorting strips across the gap. The third and fourth antenna elements are long and narrow wherein the length of the third antenna element is an integral multiple of a quarter wavelength of a first frequency and the length of the fourth antenna element is an integral multiple of a quarter wavelength of a second frequency. The first and second frequencies are the operating frequencies of the antenna. The widths of the segments of the third antenna element are not the same. The widths of the segments of the fourth antenna element are not the same. Conducting vias connect the first antenna element with the first end of the and third antenna element and the second antenna element with the first end of the fourth antenna element. A small shorting strip electrically connects the second end of the third antenna element to the second end of the fourth antenna element.  
           [0015]    A layer of second dielectric is placed between the layer of first dielectric having the first, second, third, and fourth antenna elements and a ground plane. A cavity is formed in the layer of second dielectric for a coaxial cable. The center conductor of the coaxial cable is connected to the second end of the third antenna element. The shield of the coaxial cable is connected to the ground plane. Two conducting pins connect the second antenna element to the ground plane. The antenna element can be fully encapsulated in a plastic encapsulation material having an exit port for the coaxial cable, thereby protecting the antenna assembly from the effects of the environment.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 shows a cross section view of the circuit board on which the antenna elements are to be formed.  
         [0017]    [0017]FIG. 2A shows the top view of the first and second antenna elements.  
         [0018]    [0018]FIG. 2B shows the bottom view of the third and fourth antenna elements.  
         [0019]    [0019]FIG. 3A shows a cross section view of a part of the circuit board on which the antenna elements are formed showing the conducting path between the first and third antenna elements.  
         [0020]    [0020]FIG. 3B shows a cross section view of a part of the circuit board on which the antenna elements are formed showing the conducting path between the second and fourth antenna elements.  
         [0021]    [0021]FIG. 4 shows a top view of the layer of dielectric placed between the circuit board on which the antenna elements are formed and the ground plane.  
         [0022]    [0022]FIG. 5 shows a top view of the ground plane showing the connection between a coaxial cable shield and the ground plane.  
         [0023]    [0023]FIG. 6 shows a top view of the completed antenna.  
         [0024]    [0024]FIG. 7 shows a cross section view of the completed antenna showing the connection of the center conductor of a coaxial cable to the third antenna element.  
         [0025]    [0025]FIG. 8 shows a cross section view of the completed antenna showing the conducting paths between the second antenna element and the ground plane.  
         [0026]    [0026]FIG. 9 shows a cross section view of the completed antenna which has been encapsulated in plastic.  
         [0027]    [0027]FIG. 10 shows a flow diagram of the method of this invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Refer now to FIGS. 1-9 for a description of the preferred embodiment of the antenna of this invention. FIG. 1 shows a cross section view of a layer of first dielectric material  34  having a top surface  23  and a bottom surface  25 . A first layer of conducting material  15  is formed on the top surface  23  of the layer of first dielectric material  34  and a second layer of conducting material  17  is formed on the bottom surface of the layer of first dielectric material  34 . As an example the first  15  and second  17  layers of conducting material can be a metal such as copper and formed on the layer of first dielectric material  34  by means of deposition, lamination, plating, or the like. This layer of dielectric with conducting material on the top and bottom is used to form the antenna elements of this antenna.  
         [0029]    [0029]FIG. 2A shows a top view of the layer of dielectric material with conducting layers on both the top and the bottom showing a first antenna element  12  and a second antenna element  14  formed in the first layer of conducting material using a means such as selective etching. The layer of dielectric material with conductive layers on both the top and the bottom has a rectangular shape with a first length  112  and a first width  110 . A notch  10  is removed from the layer of dielectric material with conductive layers on both the top and the bottom to accommodate and additional antenna if one is desired. The notch has a second length  116  and a second width  114 . The first antenna element  12  is separated from the second antenna element  14  by a gap having a first segment  16 A, a second segment  16 B, and a third segment  16 C each segment having a third width  22 . A first shorting strip  19  separates the second segment  16 B of the gap from the third segment  16 C of the gap and electrically connects the first antenna element  12  to the second antenna element  14 . A second shorting strip  21  separates the first segment  16 A of the gap from the second segment  16 B of the gap and electrically connects the first antenna element  12  to the second antenna element  14 . The first shorting strip  19  and the second shorting strip  21  have the same width, a fourth width  18 . The antennas&#39; resonance frequencies and resonance impedances can be fine tuned by the location of the first  19  and second  21  shorting strips of the antenna There is a conducting path  30  between the first antenna element  12  and a third antenna element and a conducting path  28  between the second antenna element  14  and a fourth antenna element. There are conducting paths,  24  and  26 , between the second antenna element  14  and a ground plane. The third and fourth antenna elements and the ground plane are yet to be described.  
         [0030]    [0030]FIG. 2B shows a bottom view of the layer of dielectric material with conducting layers on both the top and the bottom showing a third antenna element;  36 A,  36 B, and  36 C; and a fourth antenna element;  38 A,  38 B,  38 C, and  38 D; formed in the second layer of conducting material using a means such as selective etching. The third antenna element has a first segment  36 A having a fifth width  42  and a third length  118 , a second segment  36 B having a sixth width  44  and a fourth length  120 , and a third segment  36 C having the sixth width  44  and a fifth length  122 . The fourth antenna element has a first segment  38 A having the sixth width  44  and a sixth length  124 , a second segment  38 B having the sixth width  44  and a seventh length  126 , a third segment  38 C having the sixth width  44  and an eighth length  128 , and a fourth segment  38 B having the sixth width  44  and a ninth length  130 . The sum of the third  118 , fourth  120  and fifth  122  lengths is equal to an integral multiple of one quarter of the wavelength of a first frequency. The sum of the sixth  124 , seventh  126 , eighth  128 , and ninth  130  lengths is equal to an integral multiple of one quarter of the wavelength of a second frequency.  
         [0031]    The fifth  42  and sixth  44  widths are chosen to achieve the desired impedance of the third and fourth antenna elements. A third shorting strip  40  having a tenth width  52  electrically connects one end of the first segment  36 A of the third antenna element with one end of the fourth segment  38 D of the fourth antenna element. As shown in FIGS. 2B and 3A the conducting path  30  between the third antenna element and the first antenna element is located at the free end of the third segment  36 C of the third antenna element and goes directly through the layer of first dielectric  34 . As shown in FIGS. 2B and 3B the conducting path  28  between the fourth antenna element and the second antenna element is located at the free end of the first segment  38 A of the fourth antenna element and goes directly through the layer of first dielectric  34 . As an example these conducting paths,  28  and  30 , can be plated through holes, filled holes, or like. One end of the first segment  36 A of the first antenna element has a contact point  50  for connection to the center conductor of a coaxial cable.  
         [0032]    As an example the first frequency is between about 148 and 151 MHz and the second frequency is between about 136 and 140 MHz. The dimensions of the antenna are scaled to correspond to the desired frequencies and examples of some of the dimensions of the antenna will be given to correspond to the example frequencies. Those skilled in the art will readily recognize that the antenna dimensions can be scaled to operate at other frequencies. In this example the first length  112  is about 10.25 inches and the first width  110  is about 7.25 inches. The second length  116  and the second width  114  are both between about 1.0 and 1.375 inches. The third width  22  is about {fraction (1/32)} inches and the fourth width  18  is between about 0.05 and 0.25 inches, see FIG. 2A.  
         [0033]    In this example the third length  118  is about 9.125 inches, the fourth length  120  is about 5.3125 inches, and the fifth length  122  is about 4.1875 inches which is consistent with the first frequency of between about 148 and 151 MHz. In this example the sixth length  124  is about 3.635, the seventh length  126  is about 3.4375 inches, the eighth length  128  is about 8.0 inches, and the ninth length  130  is about 4.0 inches which is consistent with the second frequency of between about 136 and 140 MHz. As previously indicated the dimensions can be scaled to achieve an antenna having good operating characteristics at different frequencies.  
         [0034]    [0034]FIG. 4 shows a top view of a layer of second dielectric  56  which will be placed between the layer of first dielectric having the first, second, third, and fourth antenna elements formed thereon and a ground plane. The layer of second dielectric  56  has a first cavity  54  formed therein to enable a coaxial cable to make connections to the contact point  50  on the first segment  36 A of the third antenna element as well as to the ground plane. The layer of second dielectric  56  can also have a second cavity  58  formed therein to accommodate an edge connector, not shown. FIG. 5 shows a top view of a ground plane  70  of the antenna of this invention. The ground plane is a conducting material such as copper. The ground plane  70  has a contact region  78  to connect to the shield  74  of a coaxial cable  72 . The center conductor  76  of the coaxial cable  72  is to be connected to the third antenna element. The ground plane  70  also has connection points,  25  and  27 , to connect to the conducting paths,  24  and  26  shown in FIG. 2A, between the second antenna element and the ground plane.  
         [0035]    [0035]FIG. 6 shows a top view of the completed antenna assembly. FIG. 7 shows a cross section view of the completed antenna assembly taken along line  7 - 7 ′ of FIG. 6. FIG. 7 shows the connection of the center conductor  76  of the coaxial cable  72  to the connection region  50  on the first segment  36 A of the third antenna element and the connection of the shield  74  of the coaxial cable  72  to the connection region  78  on the ground plane  70 . FIG. 8 shows a cross section view of a part of the completed antenna assembly taken along line  8 - 8 ′ of FIG. 6. FIG. 8 shows the conduction paths,  24  and  26 , between the second antenna element  14  and the ground plane  70 . As shown in FIG. 8 all of the conducting material has been removed from this region of the second surface of the layer of first dielectric  34 .  
         [0036]    As shown in FIG. 9, the antenna assembly can be fully encapsulated in a plastic material  80  or other suitable insulating and encapsulating material. The cross section of the antenna assembly shown in FIG. 9 is also taken along line  7 - 7 ′ of FIG. 6. As shown in FIG. 9, the plastic encapsulating material  80  covers the ground plane  70 , the top of the antenna assembly, and the edges of the antenna assembly. The coaxial cable  72  extends through the plastic encapsulating material  80 .  
         [0037]    The antenna described herein can be scaled to operate efficiently at frequencies between about 3 KHz to 300 GHz.  
         [0038]    [0038]FIG. 10 shows a flow diagram of the method of forming an antenna of this invention. As shown in the first box  140 , a layer of first dielectric material having a top surface, a bottom surface, a first layer of conducting material on the top surface of the layer of first dielectric material, and a second layer of conducting material formed on the bottom surface of the layer of first dielectric material is provided. As shown in the next box  142 , the antenna elements and shorting strips are formed in the first and second layers of conducting material. As shown in the next box  144 , conducting paths are formed between the first and third antenna elements and between the second and fourth antenna elements. As shown in the next box  146 , a layer of second dielectric having a cavity for a coaxial cable formed therein is provided. As shown in the next box  148  a ground plane is provided. As shown in the next box  150 , the assembly is formed by placing the layer of second dielectric on the ground plane and the layer of first dielectric with the antenna elements formed thereon is placed on the layer of first dielectric. As shown in the next box  152  conduction paths are formed between the ground plane and the second antenna element. As shown in the next box  154 , the coaxial cable is connected to the antenna assembly. As shown in the next box  156  the assembly is encapsulated if desired. The steps shown in FIG. 10 have been previously described in greater detail.  
         [0039]    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.