Design of Absorptive Bandpass Filters With General Chebyshev Response Based on λ/4 Microstrip Lines

In this brief, a synthesis design method is proposed for one-port absorptive bandpass filters (BPFs) with general Chebyshev response and transmission zeros. The method is based on coupling matrix theory, enabling the derivation of normalized coupling matrix coefficients based on user-defined parameters, including 3 dB bandwidth, in-band reflection coefficient, and out-of-band rejection. Moreover, it offers design equations for designing absorptive filters using transmission lines, coupling lines, and stubs, all with a length of one-quarter wavelength at the center frequency of the passband. To illustrate this method, a fourth-order absorptive BPF with a general Chebyshev response and two transmission zeros is designed, fabricated, and measured. The experimental results verify the effectiveness of the design method.