CMRR analysis for widedand passive monolithic differential quadrature coupler

This paper presents the performance characteristics along with the common mode rejection ratio (CMRR) analysis of a broadband passive quadrature differential coupler implemented using GaAs technology. The coupler utilizes a multi-dielectric layer structure to achieve a broadband performance from 15 to 45 GHz in a simple coplanar configuration. A return loss better than 12 dB with isolation better than 15 dB and CMRR of 20 dB have been achieved over the entire frequency band. Also phase and amplitude mismatch within +5°and 1.5 dB, respectively have been realized over the same frequency range. This performance is especially important to the intended use with wideband double balanced mixers, and amplifiers. A slow-wave mechanism was also introduced to the coupler and has led to 14% reduction in the coupled length.