Abstract:
A non-conductive frame supports the resonators in a patch antenna assembly. The frame supports the resonators without making holes in the resonators and thereby avoids the problem of creating unwanted electric field polarizations. Additionally, the frame grasps the resonators in areas of low current density and thereby avoids creating additional disturbances in the radiation pattern. The frames may also include posts that are used to attach the frames to the feedboard without using additional components such as screws.

Description:
CROSS REFERENCE TO RELATED INVENTIONS 
     This application is related to the following commonly assigned and concurrently filed U.S. patent applications entitled “Patch Antenna”, Ser. No. 09/425,368; and “Patch Antenna Using Non-Conductive Thermo Form Frame”, Ser. No. 09/425,373. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to antennas; more particularly, patch antennas. 
     2. Description of the Prior Art 
     FIG. 1 illustrates an exploded view of a prior art patch antenna assembly. Non-conductive front housing  10  and conductive rear housing  12  form the outer surfaces of the antenna assembly. The two sections of the housing enclose multi-layered feedboard  14 , resonators  16  and  18  and spacers  20 . Spacers  20  are attached to front side  22  of feedboard  14  by screws  24 . Screws  24  mate with threads on the inside of spacers  20  by passing through holes  26  in feedboard  14 . Resonators  16  and  18  are attached to spacers  20  in a similar fashion. Screws  28  mate with threads on the inside of spacers  20  by passing through holes  30  in resonators  16  and  18 . The spacers are chosen so that they provide a space of approximately {fraction (1/10)} of a wavelength at the frequency of operation between feedboard  14  and resonators  16  and  18 . The assembled feedboard, spacers and resonators are mounted inside of the enclosure formed by front housing  10  and rear housing  12 . A signal to be transmitted by the antenna assembly is provided to conductor  40  of multi-layered feedboard  14 . Conductor  40  is typically positioned on one layer of feedboard  14  such as on top layer  42 . An insulating layer is typically provided between conductor  40  and a ground plane layer of feedboard  14 . The ground plane layer  22  normally has openings or slots  44  which allow the signal from conductor  40  to couple to resonators  16  and  18  so that the signal can be transmitted through front housing  10 . 
     FIG. 2 provides a more detailed illustration of the assembled feedboard  14 , spacers  20  and resonators  16  and  18 . Screws  24  pass through holes in feedboard  14  to mate with the threaded inside portion of spacer  20 . Similarly, screws  28  pass through holes in resonators  16  and  18  to mate with the threaded inside portion of spacers  20 . 
     This prior art patch antenna assembly suffers from several shortcomings. The assembly is expensive to assemble because of the many individual parts such as eight spacers and  16  screws. The spacers are expensive to mass produce because they include threaded inner portions. Additionally, the holes made through resonators  16  and  18  to allow screws  28  to mate with spacers  20  create unwanted patterns in the radio frequency energy radiated by the antenna assembly. For example, if the antenna is being used for a horizontally polarized transmission, the holes introduce additional non-horizontal polarizations in the transmitted signal. 
     SUMMARY OF THE INVENTION 
     The present invention solves the aforementioned problems by providing a non-conductive frame that supports the resonators. The frame supports the resonators without making holes in the resonators and thereby avoids the problem of creating unwanted electric field polarizations. Additionally, the frame grasps the resonators in areas of low current density and thereby avoids creating additional disturbances in the radiation pattern. In another embodiment of the invention, the frames include posts that are used to attach the frames to the feedboard without using additional components such as screws. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 illustrates a prior art patch antenna assembly; 
     FIG. 2 illustrates a prior art feedboard, spacer and resonator assembly; 
     FIG. 3 illustrates an exploded view of a patch antenna assembly having non-conductive frames; 
     FIG. 4 illustrates a cross section of an assembled patch antenna system having non-conductive frames; 
     FIG. 5 illustrates a non-conductive frame; 
     FIG. 6 is a cross section of the frame of FIG. 5 along line A—A; and 
     FIG. 7 is a cross section of the frame of FIG. 5 along line B—B. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 illustrates patch antenna assembly  100 . The assembly is enclosed by conductive rear housing section  112  and non-conductive front housing section  114 . Resonator elements  116  and  118  are held in non-conductive frames  124  and  126 , respectively. Posts  128  of the non-conductive frames are received by post holes  129  of feedboard  130 . Feedboard  130  is positioned in front housing section  114  by positioning tabs  132 . Feedboard  130  is multilayered and contains a ground plane, a plane containing conductor  134 , and insulating layers on the top and bottom surfaces and between conductor  134  and the ground plane. Slots  136  and  138  in the ground plane permit a radio frequency (RF) signal on conductor  134  to couple to resonators  116  and  118  so that RF energy may be transmitted through front housing section  114 . Rear housing section  112  then mates with front housing section  114  and locks in place by interacting with locking tabs  142 . Rear section  112  contains opening  144  which provides a passage through which a conductor can pass for attachment to point  148  on conductor  134 . 
     Non-conductive frames  124  and  126  include posts  128 . It should be noted that frames  124  and  126  may be manufactured using injection molding and may also be formed as one part rather than two in order to simplify assembly. Post holes  129  in feedboard  130  receive posts  128 . The frames may be held in place by melting the portion of post  128  that extends through feedboard  130  to form a mushroom cap that holds the frames in place. Resonators  116  and  118  are snapped into frames  124  and  126 , respectively. The frames hold resonators  116  and  118  approximately {fraction (1/10)} of a wavelength at the frequency of operation away from feedboard  130 . Front housing section  114  includes tabs  132  that assist in the alignment or placement of feedboard  130  into front housing section  114 . If the frames and resonators are placed into front housing section  114  before they are attached to feedboard  130 , ridges  120  and  122  assist in the alignment or placement of the frames and resonators. It should be noted that guide ridges  120  and  122  do not extend higher than non-conductive frames  124  and  126  to ensure that ridges  120  and  122  do not interfere with the {fraction (1/10)} wavelength spacing provided by the non-conductive frames. 
     FIG. 4 illustrates a cross section of antenna assembly  100 . Interlocking tabs  142  and  170  hold front housing sections  114  and  112  together. Resonators  116  and  118  are supported in frames  124  and  128 , respectively. Retention tabs  180  hold the resonators in their respective frames. As mentioned earlier, the frames may be attached to feedboard  130  using posts  128 ; however, it is also possible to maintain the relationship between the frames and feedboard using a compression force provided by rib  172  of rear housing section  112 . The placement of the frames in front housing section  114  is facilitated by guide ridges  120  and  122 . Placement of feedboard  130  is facilitated by placement tabs  132 . Rear housing section  112  includes a series of parallel ribs  172 . When sections  114  and  112  are interlocked using tabs  170  and  142 , ribs  172  press down on the components beneath them so that the components are effectively compressed between ribs  172  and the inner surface of front housing section  114 . 
     In reference to FIG. 3, it should be noted that the radio frequency (RF) signal on conductor  134  couples to the resonators through sections  149  of conductor  134  which pass over slots  136  and  138 . The desired dominant polarization direction  174  is shown. When the RF signal couples to the resonators, the higher current densities on the resonators occur on the sides of the resonators that are parallel to conductor sections  149 . As a result, side sections  152  of resonators  116  and  118  contain the higher current densities. In order to limit interfering with the higher current densities, it is desirable that frames  124  and  126  minimize contact with the resonators along side sections  152 . In order to minimize this contact, frames  124  and  126  make contact with the resonators along perimeter surfaces  154  using retention tabs and support surfaces or ridges positioned along frame sides  156  and  158 . 
     FIG. 5 illustrates frame  124 . It should be noted that frames  124  and  126  are identical and may be formed in one piece by using ribs that interconnect the two frames. The frames may be fabricated using a material such as a polycarbonate or Noryl® type plastic. (Noryl® is a registered trademark of General Electric Company.) In general, the material should have a low dielectric loss tangent. Frame surface  190  faces in the direction of the inner surface of front housing section  114  when the patch antenna assembly is constructed. Posts  128  are received in holes  129  of feedboard  130 . It should be noted that posts  128  may be inserted through the receiving holes of feedboard  130  and then heated to create a mushroom-type cap that will hold the frame in place. It is desirable that frame sides  192  do not contact the resonator because the higher current densities on the resonator occur along surfaces adjacent to these edges and contacting the high current density surfaces will interfere with the resulting radiation pattern. In general, the frame should not contact the resonator along edges that are parallel to the conductor that couples the RF signal to the resonator or along surfaces that are adjacent to those edges. Sides  156  of frame  124  include retention tabs  180  and support surface  194 . The resonator is inserted into the frame by pressing the resonator past retention tabs  180  so that the edges of the resonator are supported by surface  194  and are held against or adjacent to surface  194  by tabs  180 . 
     FIG. 6 is a cross section of the frame of FIG. 5 along line A—A. The figure illustrates posts  128 , retention tabs  180  and resonator support surfaces  194 . 
     FIG. 7 is a cross section of the frame of FIG. 5 along line B—B. Posts  128  are illustrated along with tabs  180  and support surface  194 .