A compact CPW-fed UWB BPF using combined microstrip SIR

[[abstract]]This article presents a multimode-resonator (MMR)-based ultra-wideband (UWB) bandpass filter (BPF) fed by modified coplanar waveguides (CPWs). The MMR employed in the UWB BPF is formed by combining two quarter-wavelength (λ/4) microstrip stepped-impedance resonators (SIRs) in a structure-shared fashion. The first two resonant frequencies of the inherent λ/4 SIRs and the fundamental one of the embedded half-wavelength (λ/2) resonator were designed and located inside the UWB passband. Experiments on a prototype UWB BPF were carried out for validating the filter design. The measured frequency responses show an insertion loss of less than 1 dB between the first and the last |S11| null frequencies in the UWB passband and an upper −20-dB stopband bandwidth of about 6.14 GHz