A comparative study of active and passive GaAs microwave couplers

This paper compares the design andperformanceoftwo types of wide band multi-octave MMIC couplers.Anactive coupler is based on pHEMT devices and fabricated in a GaAs foundry and a passivecouplerusescoplanar waveguide (CPW) multilayer techniques.The multilayer couplers are fabricated on GaAs semi-insulating substrate and are reciprocal and directional. The active coupler design is adapted from the distributed amplifier circuit and is non-reciprocal. On-wafer RF measurements were carried out on the fabricated multilayer directional couplers and pHEMT based couplers. A multilayer quadrature directional coupler with coupling factor of 5dB and isolation of 10dB is realized over 10 to 35 GHz. A 180 coupler using pHEMT devices realized a coupling factor of 5dB and isolation of 26.5dB over2 to 20GHz. For the first time the relative merits of the performance and implementation of these couplers are compared in view of their respective applications.