Miniature active conversion between microstrip and coplanar wave guide

Abstract

An active device, such as a field effect transistor ("FET") or MMIC, converts microwave signals between a microstrip transmission line ("microstrip") and a coplanar wave guide ("CPW"). In microstrip-to-CPW conversion using a simple FET, a gate connection is made to the microstrip signal conductor. A drain connection is made to the center conductor on the CPW. Two FET source terminals are connected respectively to each CPW ground strip. The ground strips are electrically coupled to the microstrip ground plane with a minimum length connection so the inductance common to the FET input and output is minimized. The FET can be reconnected so as to reverse the input and output, providing for conversion of signals from CPW to microstrip. Conversion from microstrip to an intermediate CPW and back to microstrip provides for mounting an intermediate circuit, such as an amplifier or other MMIC, directly on the CPW.

What is claimed is: 
     
       1. An electrical circuit apparatus for converting transmission of signals between a microstrip transmission line and a coplanar wave guide transmission line comprising: substrate means having opposite faces;   a microstrip transmission line having a signal conductor mounted on one face of the substrate and a ground plane mounted to the other face of the substrate;   a coplanar wave guide having a center conductor and two coplanar ground strips mounted on the one face of the substrate means;   means coupling the ground plane to the two ground strips; and   an active device having a control terminal, an output terminal, and a common terminal, the active device being . .mounted adjacent to the substrate.!. .Iadd.flip-mounted to the coplanar wave guide .Iaddend.with the control terminal and the output terminal each coupled to a different respective one of the signal conductor and the center conductor, and with the at least one common terminal coupled to one of the ground strips, so that the active device couples a signal between the signal conductor and the center conductor.   
     
     
       2. An apparatus according to claim 1 in which the active device is a field effect transistor. 
     
     
       3. An apparatus according to claim 1 in which the active device is a MMIC. 
     
     
       4. An apparatus according to claim 3 in which the coplanar waveguide is formed on the MMIC. . .5. An apparatus according to claim 1 wherein the 
     
     
        active device is flip-mounted to the coplanar wave guide..!.6. An apparatus according to claim . .5.!. .Iadd.1 .Iaddend.wherein the active 
     
     
        device iS also flip-mounted to the signal conductor. 7. An apparatus according to claim 6 wherein the substrate means comprises first and second coplanar substrates, with the microstrip transmission line mounted on the first substrate and the coplanar wave guide mounted on the second 
     
     
        substrate. 8. An apparatus according to claim 7 wherein the microstrip transmission line includes a signal conductor extension mounted on the second.substrate and connected to the signal conductor mounted on the 
     
     
        first substrate. 9. An apparatus according to claim 1 wherein the substrate means comprises first and second substrates, with the microstrip transmission line mounted on the first substrate and the coplanar wave 
     
     
        guide mounted on the second substrate. 10. An apparatus according to claim 9 wherein the first and second substrates have adjacent edges and the coupling means comprises conductor means extending between the adjacent 
     
     
        edges. 11. An apparatus according to claim 1 wherein the substrate means 
     
     
        comprises a unitary substrate. 12. An apparatus according to claim 11 wherein substrate has opposing lateral edges and the coupling means 
     
     
        comprises a conductive strip extending around each lateral edge. 13. An electrical circuit apparatus for processing signals comprising: substrate means having opposite faces;   an input microstrip transmission line having an input signal conductor mounted on one face of the substrate and an input ground plane mounted to the other face of the substrate;   an input coplanar wave guide having an input center conductor and two coplanar input ground strips mounted on the one face of the substrate means;   means coupling the input ground plane to the two input ground strips;   an input active device having a control terminal, an output terminal, and two common terminals, the active device being mounted adjacent to the substrate with the control terminal coupled to the input signal conductor and the output terminal coupled to the input center conductor, and the two common terminals coupled to respective ones of the input ground strips;   an output coplanar wave guide having an output center conductor and two coplanar output ground strips mounted on the one face of the substrate means;   an intermediate circuit mounted to the input coplanar wave guide and the output coplanar wave guide for processing a signal received on the input coplanar wave guide and outputting the processed signal on the output coplanar wave guide;   an output microstrip transmission line having an output signal conductor mounted on one face of the substrate and an output ground plane mounted to the other face of the substrate;   an output active device having a control terminal, an output terminal, and two common terminals, the output active device being mounted adjacent to the substrate with the control terminal coupled to the output center conductor and the output terminal coupled to the output signal conductor, and the two common terminals coupled to respective ones of the output ground strips;   means coupling the two output ground strips to the output ground plane;   whereby a signal input on the input microstrip transmission line is transmitted to and from the intermediate circuit via coplanar wave guides,   
     
     
        and output on the output microstrip transmission line. 14. An apparatus according to claim 13 wherein the intermediate circuit is on a chip flip 
     
     
        mounted to the input and output coplanar wave guides. 15. An apparatus according to claim 13 wherein the input device and the output device are 
     
     
        on a single MMIC. 16. An apparatus according to claim 15 wherein the input 
     
     
        and output coplanar waveguides are also on the MMIC. 17. An apparatus according to claim 16 wherein the MMIC is flip mounted to the input and 
     
     
        output microstrip transmission lines. 18. An apparatus according to claim 
     
     
        16 wherein the intermediate circuit is also on the MMIC. 19. An apparatus according to claim 15 wherein the intermediate circuit is also on the MMIC.