A Novel Balanced Nonreciprocal Bandpass Filter Based on Stub-Loaded Ring Time-Modulated Resonator

In this paper, a novel balanced nonreciprocal bandpass filter based on stub-loaded ring time-modulated resonators (TMRs) is proposed, which is co-designed to integrate the feed circuits and common-mode (CM) suppression circuits. The design employs the fewest TMRs necessary, which is at least two, to achieve a reverse isolation level of larger than 20 dB. This configuration also ensures the presence of two reverse isolation poles, thereby maximizing the reverse isolation bandwidth. Even- and odd-mode analysis elucidates the isolation of signals under differential mode (DM) and the suppression of noise under common mode. This approach eliminates the need for separate feed lines and complex CM noise suppression circuit designs. Furthermore, parameterization analysis is adopted to verify the modulation parameters on the impact of the circuit. A balanced microstrip nonreciprocal bandpass filter, centered at 1.5 GHz, has been designed, simulated, and experimentally verified. The measured DM forward insertion loss is 3.9 dB, and the reverse isolation is greater than 20 dB with a bandwidth of 48 MHz. The measured CM noise suppression exceeds 26.6 dB within the frequency range of 1.2 to 1.8 GHz.