Abstract:
A suspended stripline corporate feed with an orthogonal transition to a coaxial transmission line at each of its input/output ports. Alternate I/O ports are pointed in opposite directions so that devices on both sides of the feed can be serviced by the same circuit. The cover for the feed is made out of injection molded, copper plated plastic. When utilized to distribute RF energy to T/R modules in an Active Array, the feed is machined as an integral part of the heat exchanger which cools the modules.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to corporate feed networks for antenna systems. 
     Corporate feed networks are conventionally used to distribute power from transmit/receive (T/R) modules to array radiating elements. 
     Vertical distribution of RF signals in active arrays is presently accomplished by means of suspended stripline feeds with in-line coaxial interconnects. Two feeds are required for every column of T/R modules, one for the upper half of the column and one for the lower half. A typical array might require a total of 120 feeds, which make up a significant portion of the total array cost. 
     The feed housings are made entirely from machined aluminum. They are fabricated and assembled separate from the heat exchangers and installed at a higher assembly level. This method is heavy and consumes a considerable amount of space. 
     An object of this invention is to provide a feed network which can be smaller, lighter and less expensive to fabricate than conventional feed networks. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a suspended stripline corporate feed is described with an orthogonal transition to a matched coaxial transmission line at each of its input/output ports. The suspended stripline can have circuit traces plated on one side or the other or both. Alternate input/output (I/O) ports are pointed in opposite directions, so that T/R modules on both sides of the feed can be serviced by the same circuit. This reduces by half the number of feeds required for a given array. 
     According to one aspect of the invention, half of the feed housing is machined as an integral part of the heat exchanger which cools the T/R modules. The other half is made from injection molded plastic, copper plated to make the surface electrically conductive. The plastic is loaded with glass fibers so that its thermal coefficient of expansion is matched to that of aluminum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features and advantages of the present invention will become more apparent from the following detailed description of an exemplary embodiment thereof, as illustrated in the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view illustrative of a feed network embodying the invention. 
     FIG. 2 shows the feed network of FIG. 1 in assembled form. 
     FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 2. 
     FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3. 
     FIG. 5 is a cross-sectional view illustrative of an alternate interconnection technique. 
     FIG. 6 is a simplified schematic of elements of an active array system embodying this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an active array system assembly 50 embodying the present invention. The array includes a plurality of transmit/receive (T/R) modules 52 and 54 disposed respectively on opposite sides of the assembly. The assembly further includes a heat exchanger 60, and the modules 52 and 54 sandwich the heat exchanger for cooling of the modules. 
     The heat exchanger 60 includes cooling fin stock 62 sandwiched by upper and lower metal plate surfaces 64 and 66, typically formed of aluminum. The lower surface 66 is extended to form aluminum surface 66A, which in turn provides a ground plane channel 72 for a suspended stripline transmission line corporate feed circuit 70 which matches the layout of the feed circuit layout. The other ground plane channel completing the transmission line circuit 70 is defined by a feed cover 80. 
     The cover 80 is fabricated, in accordance with the invention, of injection molded plastic, and copper plated to make the surface electrically conductive. It is desired that the plastic material have a thermal coefficient of expansion matched to that of aluminum. A plastic such as polyetherimide or that marketed under the trade name ULTEM, both of which are marketed by General Electric Company, loaded with 30% by weight of glass fibers, has been found suitable for the purpose. The cover 80 has a relieved channel pattern formed therein which is the mirror image of the channel pattern formed in the surface 66A. 
     A pair of power and control signal distribution printed wiring boards (PWBs) 84 and 86 sandwich the aluminum surface member 62A, and the cover 80. The PWBs 84 and 86 carry dc power and control signals for the active elements comprising the assembly 50. 
     Alternate input/output ports for the transmission line 70 are pointed in opposite directions so that the modules on either side of the heat exchanger can be serviced by the feed comprising the transmission line 70. This is depicted generally in FIG. 1 by coaxial pin launchers 92 and 96, pointing in opposite directions, and the dielectric concentric spacer elements 94 and 98. 
     FIG. 2 shows the active array system assembly 50 in a assembled configuration. 
     FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 2. FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3. FIGS. 3 and 4 illustrate in further detail the relationship of the transmission line circuit and the coaxial pin launchers. An end of the dielectric stripline substrate board 70A is supported by a shoulder 67 of the heat exchanger plate 66A, so that the board 70A is suspended between the plate 66A and cover plate 80. As shown in FIG. 3, cover 80 is plated with a copper coating 80A. A conductive line 70B is defined on the upper surface of the substrate board 70A, thereby defining a suspended substrate stripline transmission line. The line 70B makes electrical contact with the conductive coaxial pin launcher 92 extending upwardly through a circular opening formed 104 in the cover 80. The dielectric spacer 94 supports the pin 92 within the opening 104. 
     An RF/DC flexible interconnect circuit 110 includes a flexible dielectric substrate 112, on which is defined an RF conductive trace 114. The conductive trace 114 contacts the pin launcher 92 to electrically connect to the coaxial line, thereby coupling the suspended stripline circuit 70 to the interconnect circuit 110. The trace 114 in turn leads to a connection (not shown) with circuitry comprising the T/R module 52. 
     The suspended stripline circuit 70 is also electrically coupled to the T/R module 54 located on the opposite side of the heat exchanger 60 from the module 52. This is done via the coaxial feedthrough comprising coaxial pin launcher 96 and dielectric spacer 98 fitted within circular opening 106 (shown in phantom) in the plate 66A. This coaxial feedthrough extends orthogonally to the suspended stripline circuit, but in the opposite direction from the coaxial feedthrough comprising pin launcher 92, thus allowing the suspended stripline feed network 70 to service T/R modules located on both sides of the heat exchanger. The pin launcher 96 makes electrical contact with the conductive trace 120 comprising flexible interconnect circuit 116, which also includes a flexible dielectric substrate 118. The conductive trace 120 in turn leads to a connection (not shown) with circuitry comprising the T/R module 54. 
     FIG. 5 shows an alternative embodiment of the manner for connecting the T/R modules 52 and 54 to the suspended stripline feed circuit 70. In this embodiment, the orthogonal pin launchers are connected to orthogonally disposed coaxial feedthroughs, in turn connected through short coaxial cables to coaxial feedthroughs on the T/R modules. The pin launchers 92&#39; and 96&#39; have material removed at the ends thereof to form shoulders 122 and 134, respectively. Coaxial center conductor pins 140 and 150 of respective sub-subminiature assembly (SSMA) connectors extend through bores formed in the cover 80 and in the plate 66A, and are supported by dielectric plugs 142 and 152. The ends of the pins 140 and 150 intersect the respective ends of the pin launchers 92&#39; and 96&#39; and make electrical contact therewith. Connector fittings 144 and 154 complete the respective SSMA connectors. Coaxial cables 160 and 170 electrically interconnect between these SSMA connectors and corresponding connectors 174 and 176 of the T/R modules 52 and 54, thereby completing the connection between the suspended stripline feed circuit 70; and the T/R modules 52 and 54. Covers 130 and 132 seal the exposed ends of the coaxial transitions. 
     FIG. 6 shows a simplified schematic diagram of components of an active array system 200 embodying the present invention. The system 200 includes a suspended stripline RF feed network 202 including a plated plastic housing as described above. Orthogonal coaxial transitions 204 connect the suspended stripline feed network 202 and the T/R modules 206, the T/R modules 206 are in turn connected to the array radiating elements 208. The feed network 202 further includes an I/O port 210. 
     It is understood that the above-described embodiments are merely illustrative of the possible specific embodiments which may represent principles of the present invention. Other arrangements may readily be devised in accordance with these principles by those skilled in the art without departing from the scope and spirit of the invention.