DESIGN ANALYSIS AND FABRICATION OF LUMPED-DISTRIBUTED BRANCH-LINE COUPLERS FOR COPLANAR WAVE-GUIDE MMICS

An analysis of lumped-distributed coplanar waveguide (CPW) branch-line couplers suitable for GaAs MMIC designs is presented. This investigat ion takes into account the degree of coupling, impedance transformatio n, and levels of miniaturization in order to provide a greater design flexibility for integration with uniplanar monolithic circuits. Synthe sis techniques and design graphs are given for these couplers and a mo nolithic 50-15-OMEGA version has been fabricated and tested. The coupl er's measured results show an amplitude balance of 4.7 +/- 0.3 dB, inp ut and output return losses of better than 12 and 15 dB, respectively, and an isolation of better than 20 dB over the range 14-16 GHz. This new method of designing miniaturized couplers demonstrates their suita bility for balanced amplifiers, especially when they are incorporated into CPW MMICs. (C) 1993 John Wiley & Sons. Inc.