GaAs MMIC Nonreciprocal Single-Band, Multi-Band, and Tunable Bandpass Filters

This article reports on the RF design and practical development of active MMIC single-band, multi-band, and tunable bandpass filters (BPFs) with lossless and nonreciprocal transfer functions. They are based on series-cascaded lumped-element frequency-selective cells that are coupled with MMIC-based FETs. The FETs introduce gain and counteract the loss of the lossy elements. Furthermore, due to their unilateral behavior, nonreciprocal transfer functions can be obtained. This allows for an RF codesigned filtering isolator functionality to be created within a single RF component. By cascading multiple frequency-selective cells, both single-band and multi-band transfer functions with and without transmission zeros (TZs) can be realized. The basic operating principles of the MMIC concept are first described through parametric studies on different types of frequency-selective cells. These are followed by tunable and higher selectivity design methodologies. For practical demonstration purposes, four MMIC prototypes were designed, built, and measured using a commercially available GaAs process. They include a three-cell frequency-tunable BPF, two dual-band BPFs, and a quasi-elliptic BPF.