Compact wideband bandpass filter based on double-T-shaped stub loaded resonator and loading technique for zero-voltage point

Abstract

In this article, a double-T-shaped stub centrally loaded uniform impedance resonator (UIR) is introduced and its resonant characteristics are well clarified, which provided a simple approach for triple-mode wideband bandpass filter (BPF) design. The double-T-shaped stub consists of a T-shaped stub at the center of UIR and two shunt uniform-impedance stubs at the T-shaped stub. Furthermore, loading technique for zero-voltage point is employed to guide design procedure from UIR to the proposed resonator. The resonant frequencies of the first three modes for the resonator can be free to adjust by the length of the UIR and the two kinds of stub. Finally, a compact wideband BPF is designed, fabricated, and measured. The measured results are in good agreement with the full-wave simulation results. The realized wideband filter exhibits a 3 dB fractional bandwidth of 69.1% with good in-band filtering performance, wide stopband, and sharp out-of-band rejection skirt.