A Wideband Magnetic-Free Circulator Using Spatio-Temporal Modulation of 2-pole Bandpass Filters

Abstract

Spatio-temporal modulation (STM) has been recently introduced to efficiently implement angular momentum biasing, which is a biasing technique that breaks the time reversal symmetry yielding a non-reciprocal response. In literature, several circulators have been designed using STM of triple first-order series or shunt resonators connected in Y or $\Delta$ topology. Utilizing first-order resonators leads to a narrow band response in terms of isolation and return loss. In this paper, we tackle this problem by using a 2-pole series bandpass resonators. As a proof-of-concept, the circulator is designed at 500MHz, and demonstrates a 15-dB isolation fractional bandwidth of 8.5%, insertion loss of 3.9 dB, and return loss of better than 13 dB.)