Abstract:
An ‘orthogonally stacked’ support and cooling architecture for RF signaling circuits includes a plurality of RF amplifier circuit cards mounted on edge-mountable RF printed circuit support and heat dissipation modules, that are affixed to a first side of a base plate, so that the RF circuit cards extend in a direction that is generally orthogonal to the base plate. Arranged on a second side of the base plate are RF distribution networks for the RF circuit cards. The RF signal distribution networks are RF-coupled to the RF printed circuit boards by,blind-mating, square post type multi-pin connectors through the base plate. Orienting the RF distribution networks in a plane orthogonal to the RF circuit cards and having the heat exchangers extend into gaps between the modules serves to considerably reduce the size of the architecture.

Description:
CROSS-REFERENCE TO RELATED INVENTION  
       [0001]    The present invention relates to subject matter depicted in U.S. Design Pat. No. D428,850 issued Aug. 1, 2000, assigned to the assignee of the present application and the disclosure of which is incorporated herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates in general to an RF circuit support architecture for securely retaining and providing for convective cooling of multiple printed circuit cards containing RF signaling circuits and components. In particular, the present invention is directed to a support structure in which RF printed circuit board support and cooling modules are effectively ‘stacked’ generally transverse to a first side of a base plate in mutually adjacent, spatially separated relationship. Each module includes a convectively cooled heat exchanger to which the RF printed circuit card is mounted and which extends into a gap between mutually adjacent boards. RF signal distribution networks associated with the RF printed circuit boards are disposed on the opposite side of the base plate, and are electrically (RF). coupled to the RF printed circuit boards of the modules by means of square post type multi-pin connectors that extend through the base plate.  
         BACKGROUND OF THE INVENTION  
         [0003]    A variety of communication systems are designed to be environmentally robust in terms of their hardware and signaling format. As a non-limiting example, for the case of a communication system intended for use with a plurality of UHF line-of-sight and satellite links, a multi-link transceiver mounting rack may contain diverse pieces of communication equipment, that typically include RF transmitters, RF receivers, and various digital signal processing units, which control the operation of the RF signaling components, and interface digital communications signals with attendant signal processing circuits. Since each communication link has its own dedicated signalling scheme (modulation format, link protocol, band occupancy assignment, etc.), suppliers of such equipment will typically provide each system as an integrated unit.  
           [0004]    In a conventional multi-transistor RF power amplifier, it has been customary practice to mount the power divider, power combiner, power transistors, and associated circuitry, all on the same plane. This ‘co-planar’ housing approach has several drawbacks. First, not only is considerable area required for the entire assembly, but if a divider/combiner is employed, it becomes a significant portion of the overall layout, as the length of the transmission lines is dictated by the frequency of operation. A divider/combiner is preferred over commercially available surface mount couplers because it has less power loss.  
           [0005]    Although they are relatively small sized devices, surface mount couplers require long lengths of transmission line between couplers and active circuitry, as the spacing of the active devices dictates the size of the assembly and is greater than the size of the coupler. These long lengths of transmission line dissipate power. The dissipated loss of each surface mount coupler is also greater than that of a microstrip hybrid coupler installed on a high quality dielectric. Microstrip hybrid couplers can be designed os that they occupy most of the space between the active devices and inter-connecting transmission line length is minimized. Surface mount couplers offer only a two-way power divider/combiner, so that the amplifier must have a binary number of combined stages. Properly designed cascaded hybrids can be employed to combine any number of stages from 2 to N.  
           [0006]    In addition, complexity is added to the assembly by the necessity of physically separating the power transistors and the divider/combiner (usually by means of dividing walls), in order to ensure electrical isolation. Moreover, when more than two active stages are combined, it is a challenge to deliver DC power to the center devices without compromising the RF transmission paths. One solution would be to run the DC distribution beneath the RF paths; however, this method increases the cost and complexity of the assembly. Also, it is difficult to match the performance of all of the active devices, both in gain and phase, without some provision for subdividing the assembly into smaller sub-circuits for testing. Each port of the divider/combiner and the active amplifier sections can be connectorized to allow for ease of testing and matching. This solution increases costs, due to the number of connectors required, and increases size due to the length of the connectors.  
         SUMMARY OF THE INVENTION  
         [0007]    Pursuant to the Invention, the above-described shortcomings of a conventional RF circuit housing architecture are effectively obviated by means of an ‘orthogonally stacked’ support assembly, that is configured to provide maximum power density for a given volume, while still being able to dissipate heat generated from RF components, in particular, RF power amplifier transistors. As will be described, the support architecture of the present invention arranges a plurality of RF amplifier circuit cards (each of which may include a driver stage transistor and a pair of push-pull transistors for the output stage) on associated edge-mountable RF printed circuit support and heat dissipation modules.  
           [0008]    These edge-mountable modules are affixed to a first side of a base plate, so that the RF circuit cards or boards mounted thereto extend generally in a direction that is essentially transverse or orthogonal to the base plate. Arranged on a second side of the base plate are RF distribution networks for the RF circuit cards, that may include quadrature hybrid couplers for both power divider and complementary power combiners. These RF signal distribution networks are RF-coupled to the RF printed circuit boards by means of relatively inexpensive blind mating, square post type multi-pin connectors that extend through the base plate.  
           [0009]    Thus, in the invention, rather than being placed side-by-side on a common heat sink, the active amplifier sub-circuits are effectively mounted in a ‘stacked’ modular arrangement and having individual heat sinks. For each module, the area of the transistors and associated circuitry of each RF amplifier circuit card is the same, as is the case with their associated divider/combiners on the second side of the base plate. Since the divider and combiner circuits are oriented in a plane orthogonal to the RF circuit cards, the required area and volume is considerably reduced.  
           [0010]    RF and DC connections for a respective RF circuit card are provided at one edge of a module&#39;s RF printed circuit card, with input and output RF connections spaced apart at opposite ends of the RF circuit board and DC power connected near the center of the board. In contrast, a conventional co-planar layout usually places the RF connections at opposite ends of the circuit. Thus, all of the RF amplifier circuit cards may be identical, since there are no special considerations as to the routing of DC power to centrally located cards.  
           [0011]    This adjacent parallel mounting or ‘stacking’ of the RF sub-circuit cards allows each to be individually shielded, so as to ensure very high isolation between each active RF circuit card and the power divider and combiner circuitry on the opposite side of the base plate. Also, within the RF distribution circuitry on the bottom of the base plate, the RF combiner circuitry may be electrically separated from the RF combiner by a center wall region therebetween along which DC power is provided. The three-pin configured post-type RF connectors are designed so that they are completely shielded by conductive material (e.g., aluminum) of the assembly so as to minimize electromagnetic interference (EMI) and RFI leakage. RF power may be supplied at the top of the assembly and RF output derived at the bottom, thereby providing a maximum separation to minimize feedback.  
           [0012]    DC power distribution is readily accomplished by mounting a separate circuit board to the back side of the divider/combiner support plate into which each edge-mounted RF circuit card and heat sink assembly is plugged. The design of the divider/combiner on the underside of the base plate is such that RF connections are located near the outer edge of the assembly. The area between the RF connectors, on the back side of the divider/combiner assembly, is then used to support a DC power distribution board. This area would normally be wasted space in a conventional co-planar amplifier layout. However, with the DC distribution board attached to the divider/combiner assembly, all of the RF and DC connector pins are aligned with one another, allowing a card mounting assembly to be readily blind-mated and held in position with screws. A small amount of floating of the square-post three-pin connectors allows for alignment during assembly. DC power is delivered at a common point on the top of the assembly.  
           [0013]    Advantageously, with the architecture of the invention, the active device sub-circuits can be individually tested and aligned, to ensure that the power division and re-combination is optimal, before being installed in the assembly. The stacked alignment of the RF circuit card modules ensures that the gain and insertion phase falls within certain established limits, which allows for easy repair of the overall RF amplifier by replacing a failed card with a suitably aligned spare. Conventional co-planar designs may require intensive disassembly, alignment and re-assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a diagrammatic perspective view of the RF circuit support architecture of the present invention (absent protective covers;  
         [0015]    [0015]FIG. 2 is a diagrammatic end view of the RF circuit support architecture of FIG. 1;  
         [0016]    [0016]FIG. 3 is a bottom view of the RF circuit support architecture of FIG. 1, showing an RF divider/combiner distribution network assembly;  
         [0017]    [0017]FIG. 4 is an enlarged partial sectional view of a respective RF printed circuit card assembly mounted to the base plate of the RF circuit support architecture of the present invention, taken along lines  4 - 4  in FIG. 1;  
         [0018]    [0018]FIG. 5 is an enlarged view of that portion of the diagrammatic end view of the RF circuit support architecture of FIG. 2 surrounded by circle  2 - 5 ; and  
         [0019]    [0019]FIG. 6 is an enlarged view of that portion of the diagrammatic bottom view of the RF circuit support architecture of FIG. 3 surrounded by circle  3 - 6 . 
     
    
     DETAILED DESCRIPTION  
       [0020]    Attention is initially directed to FIG. 1, which shows a perspective view of the overall configuration of the RF circuit support architecture of the present invention (absent covers for the RF circuits), for the non-limiting example of supporting (N=5) RF amplifier circuit boards within an integrated housing unit. As shown therein, a rigid, generally planar conductive base plate  10 , such as an aluminum plate, has a first side thereof  12 , upon which a plurality of edge-mounted RF circuit board modules  20  are affixed, so as to support respective RF printed circuit boards  22  in a direction that is essentially transverse (e.g. orthogonal) to the base plate  10 . The modules  20  may include protective covers (not shown) for the RF printed circuit boards. A second side  14  of the base plate  10  supports an arrangement of N (five in the present example) RF signal distribution networks  30  (e.g., combiner/divider including quadrature hybrid couplers) shown in detail in the plan view of FIG. 3 associated with RF signaling circuits of the RF printed circuit board modules  20 . Although not shown in FIG. 3, a protective cover for the RF distribution networks  30  may be attached to the base plate  10 .  
         [0021]    As further shown in the perspective view of FIG. 1, the side view of FIG. 2 and the enlarged partial sectional view of FIG. 4, a respective RF printed circuit board support and cooling module  20  is comprised of a generally planar, electrically and thermally conductive land region  21 , from a first side  23  of which project a plurality of heat exchanger fins  24  over which a cooling fluid, such as forced air, may pass, for removing heat from the circuit components of the printed circuit board module  20 . The heat exchanger fins  24  project in a direction that is substantially orthogonal to the land region  21 , and occupy the volume of space between the spaced apart modules  20  affixed to the first side  12  of the base plate  10 . As described above, this ‘orthogonal’ physical integration of the various components provides for a very efficient use of the available volume within the support structure of the invention.  
         [0022]    A first, base end  25  of the land region  21  of the RF printed circuit board module  20  terminates at a generally L-shaped flange  26 , the bottom  27  of which is configured to abut directly against the first side  12  of the base plate  10 . The L-shaped flange  26  is sized to receive mounting hardware, such as screws and the like (shown at  28  in the bottom view of FIG. 3), that are insertable through bores in the base plate  10  and may be screwed into tapped bores (not shown) in the flange  26  of the module. A second, upper end of the land region  21  has a lip  38  that defines the upper or top end portion of a respective RF printed circuit module  20 .  
         [0023]    The land region  21  of a respective RF circuit module  20  has a generally planar second side  31 , to which an RF signaling circuit board  22  is affixed, as by means of hardware fittings, such as screws  32 . As described above, as a non-limiting example, the RF signaling circuitry  33  of the printed circuit board  22  may include an RF amplifier driver stage transistor and a pair of push-pull transistors for the RF output stage.  
         [0024]    In order to provide RF connectivity to the RF signaling circuitry  33  of the printed circuit board  22 , a plurality of first multi-pin (three-pin) connectors  34  are mounted at an edge region  35  of the board  22  adjacent to the first end  25  of the land region  21  of the module  20 . In a preferred, but non-limiting embodiment, a male connector portion  35  of a mated pair of three-pin connectors  34  is mounted to the board  22 , proper. As shown in the enlarged sectional view of FIG. 4 and the enlarged side view of FIG. 5, the three-pin connector  34  has a three-pin, 0.025″ square post, male, surface mount technology (SMT) connector  35  arranged to engage a three-pin female receptacle  36 . As pointed out above, this type of square-post connector is primarily intended for DC applications, so that the cost of a mated pair is much less than typical coaxial connectors. In order to accommodate the connectors  34 , the generally L-shaped flange  26  of the module  20  is provided with an aperture or slot  29 , that is aligned with a complementary aperture  37  in the base plate  10 .  
         [0025]    Because the male connector  35  is an SMT component it may be readily installed with pick-and place (robotic) equipment. Also, the length of a mated pair of multi-pin connectors  34  is relatively small (on the order of only approximately one-half that of a typical SMA connector pair). The square-post female connector  36  is retained in the aperture  37  through the base plate  10 , so that the female connector portion  36  has a small amount of play, or ‘floats’, thereby providing for blind mating of the male and female portions of the connectors  34  within the mechanical tolerances of the orthogonal connector design of the invention.  
         [0026]    As further shown in the enlarged side view of FIG. 5, the center pin  41  of the male connector  35  is (surface mount)-attached to a section of microstrip conductor  51  of the printed circuit board  22 . The microstrip conductor  51  has a stepped size in geometry and spacing from an adjacent ground plane conductor  54  in the vicinity of its connection with the center pin width, in order to provide impedance matching compensation between the connector  34  and the microstrip transmission line of the RF printed circuit. Respective pins  42  and  43  of the male connector  35  on opposite sides of the center pin  41  are (surface mount)-attached to respective portions  52  and  53  of RF ground plane conductor  54  of the printed circuit board  22 .  
         [0027]    The enlarged side view of FIG. 5 and the enlarged partial bottom view of FIG. 6 show the female connector  36  having a center pin  61 , connected to a section of microstrip conductor  71  of a RF distribution network  30  of a printed circuit board  60  mounted to the bottom side  14  of the base plate  10 . As in the case of the connection of the male connector center pin  51  with the transmission line conductor of the RF printed circuit board  22 , the geometry of the microstrip  71  in the vicinity of its connection with the center pin width, is tailored to provide impedance matching compensation between the female connector  35  and the microstrip of the RF distribution network  30 . Measurements have shown that the mated pair of multi-pin connectors  35 - 36  has a VSWR less than 1.04:1, which is comparable with SMA coaxial connectors.  
         [0028]    The additional pins  62  and  63  of the female connector  36  on either side of center pin  61  are attached to respective pads  72  and  73  that are electrically connected (grounded) by way of conductive vias to the base plate  10 , so as to provide effective shielding for the RF signal center pins of the male and female portions of the three-pin connector  34 .  
         [0029]    The use of the orthogonal connector configuration described above, using relatively inexpensive and reduced size, multi-pin in-line connectors provides a number advantages over conventional coaxial connectors. First, coaxial connectors typically must be installed manually on the circuit in which they are used, as opposed to the use of robotic installation of the multi-pin connectors used in the invention. Also, coaxial connectors require extra room, due to the considerable length along their axis in order to mate two devices together. Multiple connections on a single assembly often require that the connectors “float” for proper alignment—something that is readily achieved by the mated connector pairs of the invention, as described above. A further shortcoming of conventional coaxial connectors is the fact that the cost per mated pair of coaxial connectors can often be a significant percentage of a unit&#39;s cost.  
         [0030]    DC power distribution to the components of the invention is readily accomplished by means of a separate DC power and control circuit board  80 , having a connector  81  and which may be mounted to the back side of the divider/combiner support base plate  10  into which each RF circuit card and heat sink module  20  is plugged. As shown in the bottom view of FIG. 3, with RF connections located adjacent to the outer edges of the modules  20 , a region or area  82  between the RF connectors  34  is employed to provide DC power distribution from the board  80 . This area  82  would normally be wasted space in a conventional co-planar amplifier layout. However, with the DC distribution board  80  attached to the divider/combiner assembly, as shown, all of the RF and DC connector pins are aligned with one another, allowing an RF module  20  to be blind-mated and retained in position.  
         [0031]    From the foregoing description, it will be appreciated that the orthogonal connector approach of the invention successfully addresses all of these issues. In place of a coax connector, a mated pair of relatively inexpensive, three-pin, surface mount connector components are used, with the male connector  35  being an SMT component that can be readily attached to the printed circuit board  22  using standard pick and place equipment. Also, in addition to the reduced length of a mated multi-pin connector pair (e.g., one-half that of a typical SMA connector pair), the square-post female connector has a small amount of float or play in the contacts, that allows for blind mating of the connector halves, within the mechanical tolerances of the orthogonal connector architecture.  
         [0032]    As described above, in terms of its effectiveness in coupling RF signals, the center pin of the three-pin connector corresponds functionally to the center conductor of a coaxial transmission line, while the two adjacent outer pins provide the ground path for this three-conductor transmission line. Depending upon the intended impedance of the transmission line, the impedance of the three-pin connector may be compensated (as by geometry sizing and shaping) to ensure that it matches a prescribed impedance (e.g., a 50 ohm transmission line).  
         [0033]    While we have shown and described an embodiment in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as known to a person skilled in the art. we therefore do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.