A Novel Balanced-to-Balanced Filtering Crossover With Wideband Isolation and Common-Mode Suppression

In this paper, a novel balanced-to-balanced (BTB) filtering crossover is proposed, which is co-designed to integrate the bandpass response and common-mode (CM) suppression characteristics without cascading the filtering networks and Baluns. Even- and odd-mode analysis is adopted to verify that the proposed BTB filtering crossover can achieve the differential-mode (DM) cross-transmission while maintaining high isolation and CM suppression. For verification of the design theory, a microstrip prototype with the center frequency f0 of 2.45 GHz is fabricated and measured. The measured DM return loss, insertion loss, and isolation are 28.7, 0.54, and 43.6 dB, respectively. For CM excitation, the measured CM suppression and isolation at f0 are 45.4 and 45.6 dB, respectively. More importantly, the proposed crossover features wideband isolation (over 20 dB) and CM suppression (over 45 dB) covering all measured frequencies from 1.0 to 4.0 GHz.