Compact Quadruple-Mode Wideband Bandpass Filter Using L-Shaped Feed-Line in a Single Cavity

Abstract

This letter presents a novel quadruple-mode cavity wideband bandpass filter (BPF). Unlike the conventional coaxial cavity resonator, the proposed cavity resonator is made up of two symmetrical conductive posts in a cylindrical cavity, while four resonant modes of the cavity resonator are classified as TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode, and a pair of TE degenerate modes (TE+ mode and TE− mode). All of the four modes are excited by a pair of L-shaped feed-lines. In addition, the four resonant modes are employed to constitute the passband of wideband BPF with a fractional bandwidth (FBW) of 45% at the central frequency of 2.2 GHz. Finally, the proposed filter is designed and fabricated. Good in-band filtering performance, wide upper stopband, and compact size are realized.