High-Selectivity Wideband Bandpass Filter Using Simple Coupled Lines With Multiple Transmission Poles and Zeros

Abstract

A compact fifth-order wideband bandpass filter (BPF) using simple coupled lines with sharp rolloff skirts is proposed in this letter. Five transmission poles within the passband and eight deep transmission zeros from 0 to $2\!f_{0}$ ( $f_{0}$ denotes the center frequency of the passband) can be realized through input impedance calculations. For demonstration, a wideband BPF prototype centered at 2.05 GHz with high-stopband rejection is designed and fabricated, whose measured 3-dB fractional bandwidth is of 60% (1.44–2.66 GHz). Good agreement between the simulations and measurements validates the design idea.