Synthesis Design of Equal-Ripple Wideband Balanced Bandpass Filter Based on Coupled-Lines and Branch-Lines

In this paper, a wideband balanced bandpass filter with equal-ripple performance with a pair of coupled-lines and four sections branch-lines and a transverse transmission line is proposed. In differential-mode (DM), the equivalent circuit exhibits a bandpass response. Meanwhile, in common-mode (CM), it exhibits a bandstop filtering characteristic. For the reason of achieving an equal-ripple DM filtering response, selecting the aspiration Chebyshev transmission function as the objective function. Moreover, a detail synthesis procedure of the DM and CM responses are studied. For verification, a prototype of equal-ripple wideband balanced BPF was designed and simulated, and the simulation results tally fairly good with the synthesis results.