Comparison of MMIC Lumped and Quasi-lumped Quadrature Coupler Performance

In this work the performance of two 90deg GaAs hybrid coupler MMICs based on lumped and quasi-lumped designs are compared for S-band operation. The quasi-lumped coupler consists of parallel lambda/8 long 50 Omega lines separated at each end by lumped capacitors, and as a consequence occupies only 0.15 the area of an equivalent lambda/4 distributed quadrature coupler. The lumped coupler is a lumped line version of a classical lambda/4 quadrature coupler. The experimental S-parameter performances for both couplers are compared. The quasi-lumped design has only 0.5 dB insertion loss as compared to 1.3 dB for the MMIC lumped hybrid. In addition the quasi-lumped hybrid offers superior return loss as well as reduced sensitivity to process variations