A Novel Balanced Nonreciprocal Bandpass Filter Based on Stepped-Impedance Resonator and Time-Modulated Resonator

Abstract

A novel balanced nonreciprocal bandpass filter based on the stepped impedance resonator and the time-modulated resonator is proposed in this paper. The balanced nonreciprocal bandpass filter is fabricated on a single PCB board, and the compact structure is achieved through the gap coupling structure of the microstrip resonators. Utilizing the quarter-wavelength transformer and gap coupling structure, good isolation between RF and modulated signals is achieved without adding lumped elements. Relying on the efficient modulation circuit and the half-wavelength stepped impedance resonator’s inherent resonance characteristic, an excellent nonreciprocal characteristic of the differential signal and effective suppression of common-mode noise are achieved. A balanced microstrip nonreciprocal bandpass filter operating at the center frequency of 1.5 GHz is designed, simulated, and experimentally verified. The measured reverse isolation is greater than 20 dB with a bandwidth of 48.8 MHz. The measured forward differential-mode insertion loss is 3.7 dB at the center frequency of 1.5 GHz. In the range of 1.2–1.8 GHz, the measured common-mode noise suppression is larger than 60.4 dB.