GaAs Filter/Isolator Using Transmission-Zero-Generating Unilateral Frequency-Selective Stages

A Ku-band GaAs monolithic microwave integrated circuit (MMIC) RF component that co-integrates the function of a quasi-elliptic bandpass filter and an RF isolator (BPFI) is reported. It is based on cascaded unilateral frequency-selective stages (UFSs) comprising a transistor-based path and multi-resonant feedback that introduces one pole and two transmission zeros (TZs). A coupled-resonator-based synthesis methodology is developed, extending conventional reciprocal filter synthesis to scalable UFS-based non-reciprocal filters. For experimental validation, a two-stage BPFI was manufactured using a 0.15-μm GaAs process. The prototype exhibits a quasi-elliptic response with center frequency of 15.9 GHz, a 3-dB fractional bandwidth of 20%, 60 dB directivity, and wide upper stopband shaped by four TZs and with greater than 20 dB rejection between DC to 12.4 GHz and 20.1 to 48.3 GHz (measured up to 38 GHz; simulated thereafter).