A Planar Dual-Wideband Bandpass Filter with Multiple Transmission Poles

A planar microstrip dual-wideband bandpass filter (BPF) with multiple transmission poles is presented in this paper. The transmission zeros and transmission poles are analyzed and calculated according to the even- and odd-mode network analysis theory and transmission line theory. A prototype with eight transmission poles was designed, fabricated, and measured. The measurement results are consistent with the simulation results, which verifies the design method. Finally, a dual-wideband bandpass filter with fractional bandwidths of 94.1 % and 27.8 % was realized. The return loss is greater than 15.6 dB in the first passband and greater than 14.5 dB in the second passband.