Abstract:
A phased array antenna system including a mandrel having compliant portions and an internally formed cooling passageway. The compliant portions are formed by removing portions of material along one end of the mandrel to form a plurality of pairs of generally U-shaped, leaf spring-like connecting areas. The connecting areas allow a degree of movement of a lower portion of the mandrel relative to the remainder of the mandrel, when the mandrel is fixedly secured to a printed wiring board (PWB). This enables flexible electrical interconnects, positioned over the compliant portions, to make electrical contact with circuit traces on the PWB, even if the PWB has a curved or undulating surface.

Description:
FIELD OF THE INVENTION 
   The present invention relates to phased array antenna systems, and more particularly to a longitudinally compliant, internally cooled phased array antenna system in which a cooling medium is flowed through an interior area of a core component to cool the core component and other electronic components supported on the core component. 
   BACKGROUND OF THE INVENTION 
   Phased array antennas are used in a variety of commercial and military applications. Typically, these antennas include hundreds of transmit/receive radiating elements that are supported adjacent one surface of a core component. Typically, the core component is made from a thermally conductive material such as aluminum. Also supported on the core component is a plurality of ceramic chip carrier boards that support a plurality of monolithic microwave integrated circuits (MMICs), phase shifters and other components. These components generate heat which is radiated through thermally conductive standoffs that are used to support the ceramic chip carrier boards closely adjacent the core component. In previously developed systems, the core component itself is supported on a cold plate. The cold plate has internally formed channels or tubes integrally formed with it to circulate a fluid through the cold plate. The fluid helps to draw heat from the core component, which in turn enables the ceramic chip carrier boards to be cooled. 
   While the above arrangement has proven to be successful in many applications, it would nevertheless be desirable to provide even more efficient cooling of the ceramic chip carrier and its components. Increased cooling ability is expected to become important as phased array antennas support even greater numbers of radiating elements and associated MMICs, phase shifters, etc., that will generate even greater amounts of heat that will need to be dissipated. 
   Thus, there remains a need to even further improve the cooling of a phased array module using a cooling medium, but which does not significantly complicate the construction of a phased array antenna, nor which limits the number of radiating/reception elements that may be employed or otherwise interferes with mounting of the ceramic chip carrier boards on a module core component. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a phased array antenna system in which a cooling medium is circulated through an elongated core component of the system to even more efficiently cool the electronic components of the antenna system during use. The core component also includes a leaf spring-like structure formed at a lower portion of the core component that allows the lower portion to flex slightly, relative to the remainder of the core component, when the core component is secured to a printed wiring board subassembly. This enables excellent electrical contact to be maintained with the printed wiring board subassembly along the full length of the core component. 
   In one preferred implementation the core component forms an elongated mandrel having both a cooling medium carrying channel formed inside, as well as a hollowed out area for allowing air to circulate within the inside area of the mandrel. The core component has a length sufficient to support a plurality of electronic component boards in side-by-side fashion, on opposing side surfaces of the mandrel. 
   In one preferred implementation the core component is formed from a solid block of aluminum. The leaf spring-like structure is formed by removing material from an interior area of the mandrel, as well as from opposing side portions, such that a plurality of U-shaped leaf spring-like sections of material are formed. The U-shaped leaf spring-like sections of material enable one end portion of the mandrel to be compliant and thus to flex slightly along its length as the mandrel is secured to a printed wiring board. A multi-layer flexible interconnect circuit assembly is coupled to the one end of the mandrel. The compliant section of the mandrel ensures that the multi-layer flexible interconnect circuit assembly makes excellent contact with conductive traces on a printed wiring board, along its full length, once the mandrel is secured to the printed wiring board. This ensures electrical communication between contacts on the printed wiring board and circuit traces formed on the flexible interconnect circuit assembly. 
   The features, functions, and advantages can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a preferred embodiment of an antenna system in accordance with the present invention; 
       FIG. 2  is a partially exploded perspective view of one module row of the antenna of  FIG. 1 ; 
       FIG. 3  is a view of the opposite side of the module row of  FIG. 2 ; 
       FIG. 4  is an exploded perspective view of a portion of the module row of  FIG. 3 ; 
       FIG. 5  is a plan view of a portion of the mandrel in accordance with arrows  5  in  FIG. 2 ; 
       FIG. 6  is a perspective view of a lower portion of the module row of  FIG. 2  with the fasteners omitted; and 
       FIG. 7  is an end view of a portion of the module row of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   Referring to  FIG. 1 , an antenna system  10  in accordance with the preferred embodiment of the present invention is shown. The antenna system  10  is illustrated as a phased array antenna system having a plurality of identical antenna module rows  12 , each of which comprises a plurality of eight element phased array antenna modules  16  supported on a printed wiring board  18 . Thus, each antenna module row  12  has  32  elements. Each module row  12  is coupled at opposite ends to a pair of manifolds  20  and  22 . Manifold  20  forms an input manifold that carries a cooling medium, for example a fluid such as water, an inert gas, or any other flowable medium capable of drawing heat from the module rows  12 , from a supply conduit  24  to supply the cooling medium to each module row  12 . Manifold  22  forms an output manifold that collects the cooling medium flowing through each module row  12  and returns the cooling medium to a radiator, heat exchanger or supply source coupled to conduit  26 . In this manner, the cooling medium flowing through each module row  12  is used to cool the electronic components on each of the modules  16 . This provides even more efficient cooling of the electronic components on each antenna module  16 . While only eight module rows  12  are shown, a greater or lesser number of module rows  12  could be implemented to suit the needs of a specific application. In the example embodiment of  FIG. 1 , the system  10  forms a 256 element phased array antenna. 
   Referring to  FIG. 2 , one module row  12  is shown in a partially exploded prospective fashion. The printed wiring board  18  has been omitted to better illustrate the structure of the antenna modules  16 . 
   Referring to  FIGS. 2-4 , each module row  12  is formed by an elongated, thermally conductive core component in the form of a metallic mandrel  28  having a plurality of components supported thereon in thermal communication with the mandrel  28  ( FIGS. 2 and 3 ). In one preferred form, the mandrel  28  is formed by a single piece of aluminum stock. The mandrel  28  supports a plurality of ceramic chip carrier assemblies  30  adjacent one another along one side surface of the mandrel  28 , and a corresponding plurality of chip carrier component assemblies  30  on an opposing side surface of the mandrel  28  ( FIG. 3 ). A plurality of conventional circulator assemblies  32  are also disposed on each side of the mandrel  28 . Each circulator assembly  32  is associated with a single one of the chip carrier assemblies  30 . Eight element antenna integrated printed wiring boards (AIPWBs)  34  are disposed on an upper surface of the mandrel  28  ( FIG. 4 ). Four flexible interconnect circuit assemblies  36  are secured at a lower end of the mandrel  28  and are electrically coupled to the ceramic chip carrier assemblies  30  using conventional wire bonds  30   a . Each flexible interconnect circuit assembly  36  may be secured by bonding, as generally described in U.S. application Ser. No. 10/991,291, filed Nov. 17, 2004, and assigned to the Boeing Company, and incorporated by reference herein. Each AIPWP  32  provides eight dual polarization radiating elements, as well as an interface to DC logic and power subsystems (not shown) associated with the antenna. 
   Referring to  FIGS. 2 ,  5  and  7 , it is a principal advantage of the antenna system  10  that each mandrel  28  includes a pair of leaf spring-like structures  38  formed at a lower end thereof. The leaf spring-like structure  38  is formed by removing material on the interior area of the mandrel  28 , as well as along lower exterior side portions  40  of the mandrel, so that the material left forms a generally sideways-facing U-shaped structure. Cut-outs  46  are also formed along the lower side portions  40  of the mandrel  28  such that a plurality of independently compliant sections  47  are formed on the mandrel  28 . When the mandrel  28  is secured to the printed wiring board  18  ( FIG. 1 ) via fastening elements  48  and  50  ( FIGS. 2 and 7 ), the entire length of the lower surface portion of the mandrel  28  can be held securely against the printed wiring board  18 . This eliminates the possibility of undulations in the surface of the printed wiring board  18 , or a slight curvature or undulations of the mandrel  28 , from preventing electrical content from being made between surface traces on the printed wiring board  18  and the flexible interconnect circuit assemblies  36 , at one or more points along the length of the mandrel  28 . 
   With further reference to  FIGS. 2 and 3 , the AIPWBs  34  may be formed in accordance with the teachings of U.S. patent application Ser. No. 10/200,088, filed Jul. 19, 2002; U.S. Pat. No. 6,670,930, issued on Dec. 30, 2003; and U.S. Pat. No. 6,580,402, issued on Jun. 17, 2003, each of which are hereby incorporated by reference into the present application, and each of which are assigned to The Boeing Company. 
   The circulator subassemblies  32  each comprise four channel open (i.e., quad) circulators that are commercially available. The circulator subassemblies  32  are in electrical communication with associated ceramic chip carrier subassembly boards  30 . Referring to  FIGS. 2 and 5 , each circulator subassembly  32  includes four permanent magnets  32   a  that project through four corresponding holes  28   a  in the mandrel  28 . Thus, there are 16 circulators for each eight element antenna module  16 . 
   Referring further to  FIG. 2 , each AIPWB  34  is positioned against a conventional, mechanically compliant spring assembly  50  that forms a thin, conductive layer for making electrical contact with a conventional honeycomb wave guide component  52  that covers each of the AIPWBs  34 . Alignment pins  52  (not shown) projecting from the mandrel  28  through each of the AIPWBs  34  enable precise positioning of the honeycomb wave guide  52  and the spring assembly  50  over each of the AIPWBs  34 . 
   Referring further to  FIGS. 2 and 3 , the mandrel  28  includes a hollowed-out area  54  and a cooling medium passageway  56 . Fastening elements  48  and  50  form attachment posts that can be threaded into openings  60  (in  FIG. 6 ) in the mandrel  28  to enable attachment of the mandrel  28  to the printed wiring board  18 . Threaded nuts  62  ( FIG. 7 ) may be used to accomplish securing of the mandrel  28  to the printed wiring board  18 . 
   While the mandrel  28  of  FIGS. 2 and 3  is illustrated as a single section of metallic material, the mandrel  28  could just as readily be formed in two or more sections that are secured together to form an elongated subassembly. However, forming the mandrel  28  from a single length of material eliminates the need for using seals, gaskets, etc., that would otherwise be needed to seal two or more sections of the mandrel together to ensure that the cooling medium flowing through the entire mandrel does not leak at the interfaces of adjacent mandrel sections. The compliant leaf spring-like structures  38  enable a single, elongated length of material to be used while still permitting each module section  16  to be secured flush against the outer surface of the printed wiring board  18 . 
   Each of the ceramic chip carrier boards  30  are preferably secured via thermally conductive adhesive to the mandrel  28 . Suitable electrically conductive adhesives are commercially available. 
   Referring further to  FIG. 6 , a bottom surface of the mandrel  28  can be seen in greater detail. The depth of each slot  46  extends upwardly past the U-shaped leaf spring-like structures  38 . Thus, the slots  46 , in combination with the leaf spring-like structures  38 , enable the length designated by dash line  66 , representing one compliant section  47 , to flex independently of adjacent compliant sections  47  along the length of the mandrel  28  when the mandrel  28  is secured to the printed wiring board  18 . 
   Referring further to  FIG. 7 , the mandrel  28  is shown clamped securely down to the printed wiring board  18 . The flexible interconnect circuit  36  makes electrical contact with traces on the upper surface  18   a  of the printed wiring board  18 . The flexing of the lower portion  42  of the mandrel  28  does not affect the flow of the cooling medium through the passageway  56 , since each compliant portion  47  of the mandrel  28  is independently secured to the printed wiring board  18 . The mandrel  28  can form slight undulations or a slight curvature along its length that conforms to undulations and/or a slight curvature of the printed wiring board  18 , to thus ensure that full contact is made along the entire length of the flexible interconnect circuit  36  and the upper surface  18   a  of the printed wiring board  18 . 
   The system  10  of the present invention thus enables an elongated core component of a phased array antenna module to be secured along its full length to a printed circuit assembly while ensuring that proper electrical contact is made along the full length of the core component with the printed wiring board to which it is secured. The internal cooling passageway incorporated into the mandrel  28  allows even more efficient cooling of the ceramic chip carrier boards used with phased array antenna systems, since the cooling medium is flowed very close to the source of the heat being generated in the module (i.e., the ceramic chip carrier boards). The use of a single length of thermally conductive material (for example, aluminum) to form the mandrel further eliminates the need for seals or gaskets to be employed, if the mandrel was to be formed in two or more independent sections and then secured together to form a single mandrel assembly. 
   While various preferred embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the inventive concept. The examples illustrate the invention and are not intended to limit it. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.