Passive-Integrated Two-Port-Quasi-Reflectionless RF Bandpass Filters With Beyond-3-dB-Bandwidth Flat Group Delay

This paper presents a class of on-chip passive-integrated RF bandpass filters (BPFs) in Gallium Arsenide (GaAs) technology. They exhibit two-port-RF-quasi-absorptive behavior and wideband flat-group-delay responses as main operational features, making them suitable for modern high-date-rate digital-communications systems. Firstly, by means of a reflective one-pole BPF and two shunt identical absorptive bandstop filters (BSFs) in a π-shape topology, an RF BPF with symmetrical quasi-reflectionless response and flat group delay beyond its 3-dB bandwidth (BW) is realized. Subsequently, in order to further improve the stopband attenuation levels of the previously-designed low-order BPF circuit, a higher-rejection counterpart is conceived using two modified single-pole reflective BPF units and three shunt identical absorptive BSF branches. The theoretical responses of both BPFs are obtained from their associated lumped-element-based equivalent circuits. For experimental-demonstration purposes, two GaAs-based proof-of-concept RF BPF prototypes are designed, manufactured, and tested. The two measured absorptive BPFs have 11.58-GHz center frequencies, quasi-reflectionless ranges from DC to 46.02 GHz and from DC to 46.66 GHz, 3-dB-BW ranges from 7.527 to 15.94 GHz and from 8.312 to 15.18 GHz, and maximum group-delay variation of ±0.0068 ns from 5.92 to 16.94 GHz and from 6.316 to 17.58 GHz, respectively.