Frequency Tunable Circulator Using Spatiotemporal Modulation of Mixed Static and Time-Modulated Resonators

This paper presents RF design methodology for frequency tunable circulator using spatio-temporal modulation. By utilizing spatiotemporal modulated static resonators with time-modulated resonators in each branch, the proposed circulator can achieve a low transmission insertion loss (IL) with flat passband response and sharp roll-off in stopband. Simulation results demonstrate that the proposed circulator exhibits two null reverse isolation and two reflection poles frequency characteristics within passband. The static resonators function as a bandpass filter, providing flat passband response and as a bandstop filter for intermodulation (IM) frequencies, resulting in significant reduction in IM signal power. For proof-of-concept, a microstrip line circulator with frequency tunable characteristics is designed and fabricated, showing continuous frequency tuning from 1.45 GHz to 1.70 GHz. Measured IL varied between 3.95 to 4.60 dB and reverse isolation ranging 19 to 40 dB at center frequency.