Balanced Full‐Passband Linear‐Phase Nonreciprocal Bandpass Filter

ABSTRACT In this paper, a balanced full‐passband linear‐phase nonreciprocal bandpass filter is reported for the first time. The nonreciprocal characteristic is realized using time‐modulated resonators. The full‐passband linear‐phase characteristic is realized by integrating group delay equalization circuits at both the balanced RF input and output ports of a balanced nonreciprocal bandpass filter. The modulation introduced by the time‐modulated resonators achieves reverse isolation of the RF signals while simultaneously altering the group delay in the forward path, resulting in a group delay characteristic that is different from that of conventional bandpass filters. In this design, the group delay is first equalized near the center frequency and then at both the edges of the passband, ultimately achieving a full‐passband linear‐phase characteristic. The balanced circuit achieves effective common‐mode suppression by employing resonators that exhibit different resonant frequencies under common‐mode and differential‐mode excitations. The fabricated microstrip prototype on an F4B substrate exhibits good agreement between measurement and simulation results, confirming the effectiveness of the proposed design.