Co-Designed Quasi-Circulator and Bandpass Filter

This paper focuses on RF co-designed front-end components that simultaneously exhibit the function of a quasi-circulator (QC) and a bandpass filter (BPF). They are based on transistor-based non-reciprocal stages that are effectively combined with a Wilkinson divider and/or passive resonators. RF front-end miniaturization is achieved through: i) a magnetic-free design method that exploits the inherent non-reciprocal properties of transistors and ii) the realization of an RF component with co-located signal processing actions. For proof-of-concept validation purposes, two QC/BPF prototypes were designed, manufactured and measured at 2.4 GHz. The first prototype exhibited a single-pole BPF response with minimum in-band insertion loss (IL) of 0.9 dB, 3-dB FBW of 18.9% and maximum isolation (IS) of 21 dB, 16.9 dB and 46 dB for respectively RF signal transmission between ports 1 and 2, 1 and 3 and 2 and 3. The second prototype exhibited a two-pole BPF response with minimum in-band IL of 0.5 dB, 3-dB FBW of 14.6%, and maximum IS of 21.3 dB, 20.3, and 47.4 dB for respectively RF signal transmission between ports 1 and 2, 1 and 3 and 2 and 3.