Abstract:
An X-Band microstrip antenna for use on a fourteen inch diameter projectile to transmit telemetry data. The X-Band microstrip antenna is configured to wrap around the projectile&#39;s body without interfering with the aerodynamic design of the projectile. The X-Band microstrip antenna operates at 7900 to 8100 MHz telemetry frequency band. Sixteen microstrip antenna elements equally spaced around the projectile provide for linear polarization and a quasi-omni directional radiation pattern.

Description:
[0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/145,234, filed Jun. 1, 2005, which is a continuation in part of U.S. patent application Ser. No. 10/817,412, filed Mar. 31, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 10/664,614, filed Sep. 19, 2003, U.S. Pat. No. 6,856,290. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a microstrip antenna for use on a weapons system to transmit telemetry data. More specifically, the present invention relates to a cylindrical shaped microstrip antenna array which operates in the X-band frequency of the electromagnetic spectrum and which is adapted for use on a 14-inch diameter weapons system such as a missile.  
         [0004]     2. Description of the Prior Art  
         [0005]     A microstrip antenna operates by resonating at a frequency. The conventional design uses printed circuit techniques to put a printed copper patch on the top of a layer of dielectric with a ground plane on the bottom of the dielectric. The frequency that the microstrip antenna operates at is approximately a half-wavelength in the microstrip medium of dielectric below the patch and air above the patch.  
         [0006]     There is currently a need to produce a quasi omni-directional radiation pattern from a conformal wrap-around microstrip antenna with a 14-inch maximum diameter and 5-inch maximum length. The antenna is to be used on a weapons system or projectile such as a missile. The required frequency of operation for the antenna is 7900 to 8100 MHz telemetry frequency band which is the X-Band frequency range of the electromagnetic spectrum.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention overcomes some of the disadvantages of the past including those mentioned above in that it comprises a highly effective and efficient microstrip antenna designed to transmit telemetry data from a missile/projectile at the X-Band frequency range of the electromagnetic spectrum. The X-Band microstrip antenna comprising the present invention is configured to wrap around the projectile&#39;s body without interfering with the aerodynamic design of the projectile.  
         [0008]     The X-Band microstrip antenna is designed to transmit telemetry data and is adapted for use on a fourteen inch diameter projectile. The microstrip antenna operates at the 7900 to 8100 MHz X-Band frequency band. Sixteen copper plated microstrip antenna elements equally spaced around the projectile provide for linear polarization and a quasi-omni directional radiation pattern.  
         [0009]     The X-Band microstrip antenna includes a feed network which consist of equal amplitude and phase power dividers. The feed network for the X-Band microstrip antenna drives the antenna elements with equal amplitude and equal phase. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of the fourteen inch X-Band microstrip antenna comprising the present invention;  
         [0011]      FIGS. 2A and 2B  illustrate the top layer of the circuit printed circuit board including the radiating elements for the fourteen inch X-Band microstrip antenna of  FIG. 1 ;  
         [0012]      FIG. 3  is a top view illustrating the bottom layer of the circuit printed circuit board for the fourteen inch X-Band microstrip antenna of  FIG. 1 ;  
         [0013]      FIG. 4  is a view illustrating the top layer of the ground printed circuit board for the fourteen inch X-Band microstrip antenna of  FIG. 1 ;  
         [0014]      FIG. 5  is a top view illustrating the bottom layer of the ground printed circuit board for the fourteen inch X-Band microstrip antenna of  FIG. 1 ; and  
         [0015]      FIG. 6  is a plot which illustrates the Voltage Standing Wave Ratio (VSWR) as a function of Frequency for the fourteen inch X-Band microstrip antenna of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Referring to  FIGS. 1, 2A  and  2 B, there is shown a X-Band microstrip antenna  10  which is a wrap around conformal antenna designed for a small projectile having a maximum diameter of fourteen inches. The maximum width W for antenna  10  is five inches. Antenna  10  operates at the X-Band frequency which is 7900 MHz to 8100 MHz.  
         [0017]     Referring again to  FIGS. 1, 2A , and  2 B, the top layer of the circuit printed circuit board  12  for microstrip antenna  10  includes sixteen half-wavelength antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44 . Equally dividing the circumference of microstrip antenna  10  into sixteen parts in the manner illustrated in  FIG. 2A  and placing a half-wavelength microstrip antenna element  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  in each part provides the required quasi-omni direction radiation pattern for antenna  10 .  
         [0018]     As shown in  FIG. 2B , there is also a three sided gap  50  formed around the top and two sides of the sixteen antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  of X-Band microstrip antenna  10 . The three sided gap  50  exposes the top surface of the dielectric substrate for circuit board  12 . The X-Band microstrip antenna&#39;s electric field is confined primarily to the three sided gap  50  around each of the antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  which is substantial different than a conventional microstrip copper antenna element where the electric field extends well beyond the antenna element.  
         [0019]     Referring to  FIGS. 2A and 3 , the feed network  52  for the antenna elements of X-Band microstrip antenna  10  is a located on the bottom layer of the circuit board  12  for the X-Band microstrip antenna  10 . The signal input  54  for each of the antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  is located at the center of each antenna element. The configuration of feed network  52 , which includes a main transmission line  57  and a plurality of branch transmission lines  59 , insures that the feed network  52  operates as an equal amplitude, equal phase power divider providing for equal distribution of RF signals with respect to the sixteen antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  42  and  44  in both amplitude and phase. The feed network  52  matches a 50 ohm input impedance to the feed networks signal input  56  to the missile&#39;s on board electronics and computer. The feed networks signal input  56  is centrally located on bottom layer of circuit board  12 . The polarization of X-Band microstrip antenna  10  is linear polarization.  
         [0020]     Referring to  FIG. 6 ,  FIG. 6  is representative of a typical VSWR measurement (plot  80  of  FIG. 6 ) for the X-Band microstrip antenna  10 . Plot  80  shows a frequency bandwidth from 7.6 GHz to about 8.4 GHZ which greatly exceeds the 7900 to 8100 MHz requirement for antenna  10 .  
         [0021]     Copper plating (designated generally by reference numeral  58  in  FIG. 2A  and reference numeral  60  in  FIG. 3 ) surrounds each of the antenna elements on the top layer of circuit board  12  and the feed network  52  on the bottom layer of circuit board  12  to reduce radiation from the feed network  52  and closely control the radiation pattern from the antenna elements.  
         [0022]     Referring to  FIGS. 2, 3  and  4 , X-Band antenna  10  includes three printed circuit boards arranged as a stack. The outside or cover board is a protective layer having the same dimensions as circuit board  12 . The outside layer, which has a thickness of 0.062 inches, is fabricated from Rogers Corporation RT/5870 commercially available from Rogers Corporation of Rogers, Connecticut. The middle layer printed circuit board in the stack is circuit board  12  and the inside layer printed circuit board for antenna  10  is the ground printed circuit board  62  ( FIGS. 3 and 4 ). Circuit board  12  and ground board  62  are each fabricated from Rogers Corporation Duroid RT/6002 which has a 0.600 inch thickness clad with one ounce copper. The dielectric material selected for boards  12  and  62  was used because of the dielectric materials extremely stable properties with large temperature variations. X-Band microstrip antenna  10  utilizes two dielectric layers, circuit board  12  and ground board  62 , because a board thickness in the board in excess of 0.060 inches for this dielectric material will cause the material to crack when bent in the configuration required by antenna  10 .  
         [0023]     The top layer of the ground printed circuit board  62  is copper plating and is identical to the bottom layer of circuit board  12  except the feed network has been removed exposing the dielectric material of circuit board  62 . The bottom layer of circuit board  12  is solid copper with a clearance hole  64  for the signal input to feed network  52  and antenna elements.  
         [0024]     As seen in  FIG. 5 , when the X-Band antenna  10  is assembled the upper portion  66  and the lower portion  68  of the ground board are removed. This leaves only the middle portion  70  of the ground board  62  when the antenna is fully assembled. The circuit board  12  and cover board also have their upper and lower portions removed when the antenna is fully assembled.  
         [0025]     Each of the printed circuit boards of X-Band microstrip antenna  10  is gold plated to protect the printed circuit boards from environmental conditions and high bonding temperatures.  
         [0026]     Referring to  FIG. 6 ,  FIG. 6  is representative of a typical VSWR measurement (plot  80  of  FIG. 6 ) for the X-Band microstrip antenna  10 . Plot  80  shows a frequency bandwidth from 7.6 GHz to about 8.4 GHZ which greatly exceeds the 7900 to 8100 MHz requirement for X-Band microstrip antenna  10 .  
         [0027]     From the foregoing, it is readily apparent that the present invention comprises a new, unique, and exceedingly useful X-Band microstrip antenna adapted for use on 14 inch diameter projectiles, which constitutes a considerable improvement over the known prior art. Many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.