A comparative study of active and passive GaAs microwave couplers

This paper compares the design and performance of two types of wide band multi-octave MMIC couplers. An active coupler is based on pHEMT devices and fabricated in a GaAs foundry and a passive coupler uses coplanar 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 5 dB and isolation of 10 dB is realized over 10 to 35 GHz. A 180 /spl deg/ coupler using pHEMT devices realized a coupling factor of 5 dB and isolation of 26.5 dB over 2 to 20 GHz. For the first time the relative merits of the performance and implementation of these couplers are compared in view of their respective applications.