Abstract:
An interconnect device for connecting components of high frequency communication systems, including RF and phased array applications. The device is capable of carrying RF and microwave signals between pairs of components and includes an outer conducting tube and an insulated conducting wire disposed within the tube. The outside diameter of the insulated wire is less than the inside diameter of the tube allowing movement of the wire relative to the tube. As a result of this movement, the longitudinal axis of the wire may vary from the longitudinal axis of the tube resulting in a “sloppy coax” interconnect. The ability of the wire to move within the tube facilitates installation and replacement of the wire when required.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is related to the connection of components in high frequency communication systems and, more particularly, to an interconnect device for RF and phased array applications. 
     RF and phased array systems include many different components. For example, a phased array system typically includes a plurality of antenna elements and modules. The modules may contain, for example, signal polarizers, amplifiers and phase shifters. The systems require that these components be connected together, so that, the signal may be passed between components. The device used to connect the components is typically referred to as an interconnect. 
     Currently, several different interconnects are in use. Some systems utilize a simple coaxial cable. The cable includes coaxial connectors at each end for connecting to the electrical components. These connectors typically take the form of SMA or GPO connectors. However, the use of coaxial cables for interconnects has certain drawbacks. The cables are heavy and at times exhibit degraded RF performance. Furthermore, the use of cables limit the density of the elements in the array. Current phased array system requirements demand an increase in the number of antenna elements within a given area. The bulky coaxial cables and the associated connectors limit the amount of antenna elements that may be placed in a given array. 
     In other systems, connections are made directly between components without the size of the cables. Each component includes a typical connector (e.g., General Purpose Outlets (“GPO”) or Subminature-A (“SMA”)) adapted to be attached to a similar connector located on the other component to be connected to. The use of a direct connection requires that the two components being connected be coaxial aligned. This constraint on positioning further limits the available configurations of components and performance of the system. 
     Other systems include coaxial cables without end connectors. In these systems, the cables are typically soldered to the components. These systems may avoid the drawbacks associated with the use of connectors however, heavy and bulky cables are still required. 
     Still other systems in use do not include coaxial cables or connectors. These systems require more complicated elements to attach the components together. These elements may often include, for example, jumpers, bridges and ribbon/wire bonds. An interconnect of this type typically has a complex design specifically tailored for the configuration of a particular system. The assembly, rework and repair processes are quite difficult due to the complex connections. Furthermore, RF performance is typically degraded by the use of these elements. 
     All of the current interconnect devices are difficult to rework or repair. Currently, there are no simple procedures associated with replacing a failed interconnect device. Rework and repair typically requires major disassembly and reassembly. 
     As discussed above, current interconnect devices have many shortcomings. It is an object of the present invention to obviate many of these shortcomings and to provide a novel interconnect device and method. 
     It is an object of the present invention to provide a novel interconnect device and method that may be easily manufactured, assembled, and repaired. 
     It is another object of the present invention to provide a novel interconnect device and method that permits the optimal geometric orientation and density of components to be employed by supporting interconnection between non-planar, non-parallel and/or nonorthogonal components. 
     It is yet another object of the present invention to provide a novel interconnect device and method that exhibits high performance requirements regardless of the geometric configuration of the components to be connected. 
     It is still another object of the present invention to provide a novel interconnect device and method applicable to a variety of RF applications. 
     It is a further object of the present invention to provide a novel interconnect device and method that meets microwave frequency performance requirements. 
     It is yet a further object of the present invention to provide a novel interconnect device and method that provides consistent performance for each interconnection made. 
     It is still a further object of the present invention to provide a novel interconnect device and method that is lightweight in order to support space based applications. 
     These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of an interconnect device according to the present invention. 
     FIG. 2 is an end view of the interconnect device of FIG.  1 . 
     FIG. 3 is pictorial view of a tray containing antenna elements and modules connected by interconnect devices according to the first embodiment of the present invention. 
     FIG. 4 is a cross-sectional view taken through lines A—A of FIG. 3, showing the first embodiment of the interconnect device. 
     FIG. 5 is a partial view of FIG. 3, showing the first embodiment of the interconnect device. 
     FIG. 6 is an end view of the system of FIG. 3, including a partial cutaway, showing antenna elements and the first embodiment of the interconnect device. 
     FIG. 7 is a cross-sectional view of a tray similar to that in FIG. 3, showing a second embodiment of the interconnect device. 
     FIG. 8 is a plan view of a tray similar to that in FIG. 3, showing the second embodiment of the interconnect device. 
     FIG. 9 is a cross-sectional view of a tray similar to that in FIG. 3, showing a third embodiment of the interconnect device. 
     FIG. 10 is plan view of a tray similar to that in FIG. 3, showing the third embodiment of the interconnect device. 
     FIG. 11 is a cross-sectional view in elevation depicting the connection between an interconnect device according to the present invention and an antenna element of a phased array system. 
     FIG. 12 is an end view in elevation of the antenna elements of FIG. 11 showing the connection between several antenna elements and several interconnect devices. 
     FIG. 13 is a cross-sectional view in elevation depicting the connection between an interconnect device that includes a tab attached to the conducting wire and an antenna element of a phased array system. 
     FIG. 14 is a plan view of the device depicted in FIG.  13 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the figures, like numerical designations indicate identical elements on all figures. The interconnect device  40  of the present invention, as shown in FIG. 1, may include an outer tube  43 , a conducting wire  45  and a layer of insulator  47 . The outer tube  43  is conductive and is formed from a light weight conductive material such as aluminum or copper. A light weight interconnect is preferred due to its potential use in several space based applications. The conducting wire  45  may be any suitable conductor such as, for example, copper or gold. The wire  45  is coated with an insulator  47 . The insulator  47  may be formed from a suitable conventional dielectric material, such as TEFLON (i.e. polytetrafluoroethylene (PTFE)). 
     The outer diameter of the insulated coating  47  is less than the inner diameter of the conducting tube  43 . As a result, a gap or space  41  is present between the inside of the tube  43  and the insulated wire  47 . As shown in FIG. 2, the difference in diameter permits the axis of the insulation  47  and wire  45  to deviate from the axis of the tube  43 . The tube  43  and wire  45  are not coaxial but, may be said to have “sloppy” or approximate coaxial relationship. The gap  41  permits the insulated wire  45  to be inserted and removed from the tube  43  with relative ease. TEFLON is preferred for use as insulator  47  due to its relatively smooth surface. While the interconnect  40  has been discussed with reference to a tube with a cylindrical cross-section, the tube cross-section may be modified to suit the particular system design. 
     The interconnect device  40  described above, may be employed in a wide range of systems. These systems include, for example, phased array antenna structures, communication payload RF electronics, radar electronics and other wireless communications. The frequency carried by the interconnect may exceed 20 GHz and may range up to the cut-off frequency of the tube size chosen. In a phased array RF system the interconnect may typically carry a signal of approximately 26 GHz. 
     The interconnect device  40  according to the present invention may be used with a RF phased array antenna system, as depicted in FIG.  3 . The system includes a plurality of antenna elements  20  and RF modules  30  mounted on a support tray or housing  10 . As described above, the modules  30  may perform numerous functions such as signal amplification and polarization. The entire system typically includes a plurality of trays  10  in a stacked configuration. The trays are typically formed from a suitable high strength and light weight material such as aluminum or aluminum beryllium. 
     The antenna elements  20  may be connected to the modules  30  through the use of the interconnect device  40 , as disclosed in FIG.  3 . Interconnect  40  includes a conducting wire  45  with an insulator  47 . (See FIG. 1) The tube may have an outside diameter of between about 31-37 mils and an inside diameter of between about 23-29 mils. The dielectric layer may have an outside diameter of between about 18-22 mils. The conducting wire may have a diameter of between about 6-10 mils. The dimensions of the elements of the interconnect  40  may be modified to suit the particular use. In a preferred embodiment, the outer tube  43  has an outside diameter of 34 mils and an inside diameter of 26 mils. The outside diameter of the insulated wire is approximately 20 mils. The conducting wire has a diameter of 8 mils. 
     The interconnect device  40  may be secured to the tray  10 , as shown in FIG.  4 . The tray  10  is constructed to include ridges  13  and  15 , see FIG. 3, to provide support to the device  40 . The ends  42 ,  44  of the tube  43  may be secured to the ridges  13 ,  15  of the tray  10  by brazing or other suitable procedure. The brazing operation may adversely affect the layer of insulation  47  surrounding the wire  45 . As a result, the outer rube  43  is typically mounted to the tray  10  prior to the insertion of the insulated wire  45 . As described above, the “sloppy coax” design of the interconnect  40  permits the insulated wire  45  to slide easily into the tube  43 . 
     The tube  43  may be preformed to suit the dimensions required by the tray  10 . The ends  42 ,  44  of the tube may have different spatial coordinates in all three dimensions, as shown in FIGS. 5 and 6. The tube may be bent as required to support the connection between the elements  20  and the modules  30 , as shown in FIG.  4 . 
     A second embodiment of the interconnect device may be formed without the use of the outer conducting tube  43 , as shown in FIGS. 7 and 8. Instead, the wire  45  and insulated coating  47  are located within a hole  50  in the tray  10 , see FIGS. 7 and 8. Together the hole  50 , wire  45  and insulation  47  form the interconnect. Hole  50  is preferably drilled into tray  10 ; however, any hole forming procedure capable of creating a smooth passage of relatively precise size is acceptable. The outside diameter of the insulation  47  is sufficiently less than the inside diameter of the hole or bore  50  in order to permit easy insertion and removal of the wire. The bore  50  and the insulation  47  have the same relationship as the tube  43  and insulation  47 , as shown in FIG.  2 . The conductive enclosure provided by tube  43  has been replaced by passage  50  in the tray  10 , as shown in FIGS. 7 and 8. As described above, the tray  10  is preferably formed from a strong light weight conductor, such as aluminum, beryllium-berylliumoxide or aluminum-beryllium. 
     A third embodiment of the interconnect device is formed by placing a dielectric coated wire  45  into a slot or channel  60  in the tray  10 , as shown in FIGS. 9 and 10. As with the second embodiment, no outer tube  43  is required. The depth of the slot  60  may vary. The depth of slot  60  may be approximately twice the diameter of the insulated coating  47 , as shown in FIG.  9 . Alternatively, slot  60  may be shallower and a cover (not shown) placed over the trench to form an enclosure around wire  45 . Slot  60  may be formed in a variety of different shapes and sizes depending on the type and the configuration of the components to be connected and the available tooling, e.g., polygonal or elliptical in cross-section. 
     The design of interconnect  40  facilitates a novel method of constructing a phased array system. This method includes providing a housing or support tray  10 , such as the one depicted in FIG.  3 . The tray  10  is configured as necessary to receive the various components of the system, such as the antenna elements  20 , the modules  30  and the interconnect devices  40 . The tray configuration may include, for example, ridges  13 ,  15  to support interconnect devices. When the interconnect devices take the form of an alternative embodiment, the required holes  50  or slots  60  are created prior to attaching the various components to the tray  10 . After the tray is provided, the antenna elements  20 , modules  30  and outer tubes  43  are secured to the housing or support tray  10 . The tube  43  may be secured to the housing by brazing or other suitable process. 
     Preferably, after the tube  43  is secured to the housing, the insulated wire  45  may be inserted into the tube. The wire  45  may be connected to the antenna element  20  and module using a soldering process. Alternatively, when a gold wire is employed a thermo-compression weld bonding process may be employed. The wire  45  may be attached to a microstrip in contact with the component to be connected. In addition, a conductive tab may be used on the end of the wire  45  to facilitate attachment to the components. 
     The interconnect may be connected to the antenna element  20  in any suitable manner. This connection might include for example, a microstrip line as shown in FIGS. 11 and 12. By way of example, a typical antenna element  20  including active and parasitic components is disclosed in FIG.  11 . Element  20  may include a substrate  70  overlying the housing  10  and secured thereto by a suitable conventional adhesive  82 . Substrate layer  70  may be a conventional dielectric material such as ceramic and glass loaded PTFE (e.g. Rogers DUROID 6002). The adhesive layer  82  may be a pressure sensitive acrylic adhesive such as 3M Y966. Partially overlying the substrate is an active patch  72  of a conductor layer, typically copper. The active patch includes a microstrip line  73 . The microstrip facilitates the connection between the conducting wire  45  and the active element of the antenna. The wire  45  may be soldered to the microstrip  73 . Also overlying the substrate is a foam spacer  80 , which may be any suitable conventional material, exhibiting a low dielectric constant such as a rigid methacrylimide foam. The spacer  80  may be bonded to the substrate using an adhesive layer  78 . Similar to the lower adhesive layer  82 , layer  78  may be formed from 3M Y933. Overlying the spacer  80  is a parasitic patch of conducting material  76 . The element  20  may further include an adhesive layer  74  to connect the patch  76  to the spacer  80 . The adhesive layer  74  may be any suitable adhesive layer including bonding films such as ARLON 6700 CuClad 6250 thermoplastic or 3M Y966 acrylic. 
     The three embodiments of the present invention discussed above, may be further modified to include a conductive tab  90  to connect the microstrip  73  of the active patch  72  to the wire  45 , as shown in FIGS. 13 and 14. During construction of the antenna structure the tab  90  is aligned with microstrip  73  and soldered in place. A Sn62/Pb36/Ag2 solder preform coated with 1 percent RMA may be utilized during the soldering process. The use of resistance soldering equipment is preferred. The soldering may take place without damage to the substrate. An 800 msec reflow may be utilized without causing damage to the dielectric substrate  70 . Furthermore, use of a titanium thermode may minimize indentation in the copper patch  72 . 
     While, the figures depict the use of the interconnect between antenna elements and modules, the interconnect device may support interface between many different components. For example, the interconnect may be used to make the following connections: module to module, module to substrate, module to connector, module to element, substrate to connector, substrate to element, connector to element. 
     While preferred embodiments of the present invention have been described, it is to be understood that the embodiments described are illustrative only and the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalence, many variations and modifications naturally occurring to those of skill in the art from a perusal hereof.