A wideband bandpass filter with wide upper stopband using stepped-impedance cascadable 180 degrees hybrid rings

Abstract

This letter proposes a wideband bandpass filter by cascading two 3-dB stepped-impedance. cascadable 180 degrees hybrid rings with a pair of stepped-impedance lines. Thanks to the stepped-impedance lines, a broad upper stopband is achieved. The stepped-impedance vertically installed planar (VIP) coupler is used to implement the ideal 180 degrees phase inverter and crossovers. The experimental results show that this 2-GHz center frequency, fourth order filter has a 10-dB return loss bandwidth of 92.5% and upper stopband rejection levels of better than -20 dB up to 6.8, GHz. This proposed filter achieves wide passband and broad stopband performance simultaneously.