Multi-Functional Ultrawideband BPFs with Reconfigurable Absorptive and Tunable Attenuation Characteristics

This paper presents a new class of wideband RF codesigned bandpass filters (BPFs) with two distinct reconfigurable modes of operation. It is based on cascaded BPF stages, each one formed by a resistively-terminated asymmetric coupled-line section and two resistively-connected stubs that are at its RF input/output ports. Reconfigurability is achieved by readily altering the values of the resistive terminations. Specifically in its Mode 1, it functions as a highly-selective absorptive BPF. In Mode 2, it functions as a bandpass filter-attenuator with variable attenuation levels. To validate the proposed concept, two multifunctional example BPF configurations (one-stage and two-stage) were designed, built and tested. In Mode 1, the BPFs achieved an ultra-wide fractional bandwidth of 200% (measured at -10 dB) and provided an out-of-band rejection exceeding 30 dB. When operating in Mode 2, the BPFs demonstrated wideband operation from 0.85-3.0 GHz, with ultra-wide adjustable attenuation ranging from 1.28-35 dB.