Synthesis design of quad‐band bandpass filter with mixed frequency transformation method

Abstract

AbstractThis paper presents an analysis method to design quad‐band bandpass filters (BPFs) based on the mixed frequency transformation method. The frequency mapping technique is employed to obtain the design parameters by defining the frequency ranges of each passband. By using the proposed approach, the resonant angular frequencies and susceptance slope parameters can be obtained analytically. To validate our theory, a third‐order Chebyshev BPF and a fourth‐order elliptic BPF with different bandwidths are successfully synthesized. Moreover, a second‐order test BPF with a Chebyshev approximation and 20 dB passband return loss is synthesized, designed, fabricated, and measured. The measured insertion losses are 1.82, 2.01, 3.12, and 2.51 dB for each passband and measured return losses are better than 15.2 dB for all passbands. The measured results verify the designed BPF and also confirm the theoretical prediction.