Design of Compact and Sharp-Rejection Ultra Wideband Bandpass Filters Using Interdigital Stepped-Impedance Resonators

In this paper, a compact ultra-wideband bandpass filter (UWB-BPF) using pseudo-interdigital stepped-impedance resonators (PIDT-SIRs) is designed and implemented on a commercial printed circuit board (PCB) of RT/Duroid 5880 substrate. The first two resonant modes of the SIR are coupled together and they are applied to create a wide passband. The proposed filter at center frequency f0 of 7.1 GHz has very good measured characteristics including the bandwidth of 3.68–10.46 GHz (3dB fractional bandwidth of 95%), low insertion loss of −0.5±0.4 dB, sharp rejection due to two transmission zeros in the passband edge created by the inter-stage coupling. Experimental results of the fabricated filter show a good agreement with the predicted results. key words: ultra-wideband, pseudo-interdigital, stepped impedance resonators, transmission zeros, bandwidth