Novel quasi‐reflectionless balanced bandpass filters using absorption network for common‐mode and harmonic suppression

Abstract

Quasi‐reflectionless balanced bandpass filters (BPFs) using absorption network for common‐mode (CM) rejection and stopband extension are proposed and demonstrated. First, a quasi‐reflectionless balanced BPF is constructed by using absorption network and a uniform impedance resonator (UIR), where absorption network consists of lossy stubs loaded at both the input/output port and the ends of the coupling line (CLs). Owning to the resonating of absorption network, a three‐pole balanced BPF with CM and differential‐mode (DM) reflectionless performance are realized. Meanwhile, harmonic of DM is suppressed by exploring the loading position of the resistor. Second, to improve the selectivity of the filter, two open stubs are symmetrically loaded to the center of the UIR, a five‐pole quasi‐reflectionless balanced BPF with two transmission zeros are presented. Both proposed quasi‐reflectionless balanced BPFs are fabricated and measured. The measured results are in good agreement with the simulated ones, verifying the proposed design concept.