Miniaturized Signal-Interference Bandpass Filters Using Resonant RF Signal Paths

This paper presents a new class of miniaturized signal-interference bandpass filters (BPFs) using resonant signal-interference (RSI) stages. Miniaturization is achieved through: i) an RSI BPF stage in which series- and parallel-type resonators are incorporated in its two RF signal paths and ii) the realization of high-order filtering transfer functions by directly cascading in series multiple RSI stages-i.e., without the need for inter-stage impedance inverters. The operating principles of the proposed RSI-based BPF concept are demonstrated through various theoretical examples using linear-circuit analysis. Furthermore, for proof-of-concept demonstration purposes, a microstrip prototype was designed, built, and measured at S-band with the following RF performance characteristics: center frequency of 2.6 GHz, 3-dB absolute bandwidth equal to 633 MHz, minimum in-band insertion loss of 0.8 dB, and in-band group-delay variation between 1.2-3.2 ns.