Compact UWB bandpass filter with triple notched bands using quadruple-mode resonator

Abstract

In this letter, a compact ultra-wideband (UWB) bandpass filter (BPF) with triple notched bands is presented. The basic UWB BPF is realized by feeding a modified multiple-mode resonator (MMR) properly with two aperture-backed interdigital coupled lines. The modified MMR can create five modes in band and two transmission zeros near the lower and upper cutoff frequencies, improving passband selectivity greatly. Then, triple notched bands, together with another transmission zero in the upper stopband, are generated by implementing a coupled quadruple -mode resonator which provides a high degree of adjusting freedom. To validate the design theory, a microstrip UWB BPF with three notched bands centered at 3.6, 5.8 and 8.0 GHz, respectively, is designed and fabricated. The simulated and measured results are in good agreement and show good in-band filtering performance and sharp selectivity.