Quasi‐Absorptive Single‐Ended and Balanced BPFs With All‐Frequency Absorption and High Selectivity

ABSTRACT In this paper, quasi‐absorptive single‐ended and balanced bandpass filters (BPFs) with all‐frequency absorption and high selectivity are proposed based on the double‐sided parallel‐strip line (DSPSL). The quasi‐absorptive single‐ended BPF is composed of a ring resonator and a pair of absorptive sections. With the absorptive sections, the performance of all‐frequency absorption and wide stopband is achieved. Moreover, an out‐of‐phase coupled DSPSL structure is proposed, which has intrinsic all‐frequency and high‐level common‐mode (CM) suppression. Therefore, the design procedure of balanced filters can be simplified greatly. Based on this structure and the proposed single‐ended BPF, a novel quasi‐absorptive balanced BPF is also designed. The differential‐mode (DM) performance of all‐frequency absorption, wide stopband, and high selectivity is achieved. Meanwhile, the broadband CM suppression is realized. For experimental demonstration purposes, two quasi‐absorptive BPFs are designed and fabricated. The measured results are in good agreement with the simulated ones.