Abstract:
A TM microstrip antenna designed to transmit telemetry data for use by a fourteen inch diameter projectile. The microstrip antenna is configured to wrap around the projectile&#39;s body without interfering with the aerodynamic design of the projectile. The TM microstrip antenna operates at the 2200 to 2300 MHz TM frequency band. Eight microstrip antenna elements equally spaced around the projectile provide for linear polarization and a quasi-omni directional radiation pattern.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 10/817,412, filed Mar. 31, 2004, now U.S. Pat. No. 7,009,564, 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 
   1. Field of the Invention 
   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 TM cylindrical shaped microstrip antenna array having a GPS band stop filter which transmits telemetry data and which is adapted for use on a 14-inch diameter weapons system such as a missile. 
   2. Description of the Prior Art 
   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 layer. 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. 
   There is currently a need to provide 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 2200 to 2300 MHz telemetry (TM) frequency band. The antenna must also provide for additional isolation of RF noise from the TM transmitter on the 14-inch diameter missile at the GPS L1 frequency band which is 1565 to 1585 MHz. 
   SUMMARY OF THE INVENTION 
   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 for use at a receiving station. The 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. 
   The TM microstrip antenna is designed to transmit telemetry data and is adapted for use on a fourteen inch diameter projectile. The TM microstrip antenna operates at the 2200 to 2300 MHz TM frequency band. Eight microstrip antenna elements equally spaced around the projectile provide for linear polarization and a quasi-omni directional radiation pattern. 
   The TM microstrip antenna includes a feed network which consist of equal amplitude and phase power dividers and a GPS band stop filter at the GPS L1 frequency band so that noise from the TM transmitter will be reduced to an acceptable noise level of approximately 50 decibels. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the TM microstrip antenna comprising the present invention; 
       FIG. 2  is a view illustrating the top layer of the circuit printed circuit board for the TM microstrip antenna of  FIG. 1 ; 
       FIG. 3  is a view illustrating the bottom layer of the ground printed circuit board for the GPS antenna of  FIG. 1 ; 
       FIG. 4  is a plot illustrating a voltage standing wave ratio plot for the GPS microstrip antenna of  FIG. 1 ; and 
       FIG. 5  is a view illustrating the three dielectric layers stacked on top of one another which form the GPS microstrip antenna comprising the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 and 2 , there is shown a TM microstrip antenna  10  which is a wrap around conformal antenna designed for a small projectile having a maximum diameter of fourteen inches which equates to a maximum radius R of seven inches. The actual radius of the antenna  10  is 6.969 inches. The maximum width W for antenna  10  is five inches. Antenna  10  operates at the TM Band centered at 2.25 GHz. The frequency of operation is 2200 to 2300 MHz telemetry (TM) frequency band and there is a band stop filter requirement at the GPS frequency range of 1565 to 1585 MHz. Antenna  10  provides for quasi-omni directional radiation pattern coverage. 
   Referring again to  FIGS. 1 and 2 , the top layer of the circuit printed circuit board  12  for microstrip antenna  10  includes eight half-wavelength antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26  and  28 . Equally dividing the circumference of GPS microstrip antenna  10  into eight parts in the manner illustrated in  FIG. 2  and placing a half-wavelength microstrip antenna element  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26  and  28  in each part provides the required quasi-omni direction radiation pattern. The bottom layer of circuit printed circuit board  12  comprises dielectric material. The antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26  and  28  have a rectangular shape and are fabricated from etched copper. 
   The top layer of the circuit printed circuit  12  board includes a feed network  30  and a signal input  32  which receives telemetry data from the weapon&#39;s on board telemetry system. The signal input  32  is located at the center of the top layer of circuit printed circuit board  12  as shown in  FIG. 2 . One end of a single quarter wavelength open-circuited stub  34  tuned at the GPS frequency band is connected to signal input  32 . The open-circuited stub  34  forms a GPS band stop filter that substantially reduces noise from the TM signal at the GPS frequency band, which is 1565 MHz to 1585 MHz. An acceptable noise level reduction may be for example 50 decibels. 
   The open circuited stub  34  is also connected to the feed network  30  for TM microstrip antenna  10 . The feed network  30  drives each of the microstrip antenna elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26  and  28  of antenna  10  with equal amplitude and equal phase. The feed network  30  includes a main transmission line  36  and eight branch transmission lines  38 . 
   The two end antenna  14  and  28  elements located at each end of the circuit printed circuit board  12  are of an equal phase because the lengths of the transmission line to the antenna elements  14  and  28  form the signal input  32  are identical. The remaining antenna elements  16 ,  18 ,  20 ,  22 ,  24  and  26  are also equal phase but may differ by a multiple of 360 degrees. The configuration of feed network  30  insures that the feed network  30  operates as an equal amplitude, equal phase power divider providing for equal distribution of RF signals with respect to the eight antenna elements  12 ,  14 ,  16 ,  18 ,  20 ,  22 ,  24 , and  26  in both amplitude and phase. The feed network  30  matches a 50 ohm input impedance to the signal input  32 . The polarization of TM microstrip antenna  10  is linear polarization. 
   Referring to  FIGS. 1 ,  3  and  5 , TM microstrip antenna  10  comprises three Printed Circuit Board layers  12 ,  44  and  46  stacked on top of one another in the manner illustrated in  FIG. 5 . The outside layer  46  is a protective layer having a thickness of 0.062 inches and is fabricated from Rogers Corporation RT/5870. The middle Printed Circuit Board layer is Circuit Printed Circuit Board  12  and the inside layer is the Ground Printed Circuit Board  44 . Both the Circuit and Ground Printed Circuit Boards are made from Rogers Corporation&#39;s Duriod RT/6002 with a 0.060-inch thickness clad with one-ounce copper. The material used for the Circuit and Ground Printed Circuit Boards were selected because of their extremely stable properties with respect to temperature. Two layers are required because a thickness in excess of 0.060-inch would result in cracking when the Printed Circuit Boards  12  and  44  are bent into the configuration required by antenna  10 . As shown in  FIG. 5 , the bottom layer of the Ground Printed Circuit Board  44  is solid copper with a clearance hole  48  for the signal input  32 . The top layer of the Ground Printed Circuit Board  44  and bottom layer of the Circuit Printed Circuit Board  12  have no copper resulting in a dielectric surface. The Printed Circuit Boards  12 ,  44  and  46  are gold plated to protect the boards from environmental conditions and a high bonding temperature. 
   An SMA female chassis mount connector is installed on the inside of the antenna  10  at the input location  32  to connect antenna  10  to the weapons system on board telemetry system. 
   Referring to  FIG. 4 , the Voltage Standing Wave Ratio (VSWR) for antenna  10  was measured and a typical response is shown in  FIG. 4 . It should be noted that the VSWR is less than 2:1 over most of the 2200 to 2300 MHz TM frequency range. 
   Referring to  FIGS. 3 and 5 , the ground printed circuit board  44  of TM microstrip antenna  10 , has an upper portion boarder  50  (depicted in  FIG. 3 ) above the copper plated middle portion  52 , and a lower portion or border  54 . The boarders  50  and  54  of ground printed circuit board  44 , which each have a width of 0.50 of an inch, are machined off during the fabrication process for TM microstrip antenna  10 . Printed Circuit Boards  12  and  44  also have 0.50 inch upper and lower portions or boarders which are machined off during the fabrication process for TM microstrip antenna  10 . Alignment holes  56  are centrally located in the boarders  50  and  54  of board  44  as well as boards  12  and  46 . The alignment holes in each of the boards  12 ,  14  and  46  are used to align the Printed Circuit Boards  12 ,  44  and  46  during the high temperature bonding process which bonds the boards  12 ,  44  and  46  together. The alignment holes  56  have a ¼″ diameter. 
   When TM microstrip antenna  10  is fully assembled only the copper plated middle portion  48  of circuit board  52  remains. The middle portion of the circuit printed circuit board  12  which includes the antenna elements and feed network, as shown in  FIG. 2 , is the only portion of board  12  which remains when the fabrication of the TM microstrip antenna  10  is complete. The 0.5 inch boarders of each printed circuit board  12 ,  14  and  44  are machined off after the boards are bonded together. 
   Mounting holes are placed as required along both edges of the TM microstrip antenna  10  within 0.375 inch from each edge of the antenna  10 . 
   From the foregoing, it is readily apparent that the present invention comprises a new, unique, and exceedingly useful TM 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.