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

Cheng-Yuan HUNG  Min-Hang WENG  Yan-Kuin SU  Ru-Yuan YANG  Hung-Wei WU  

IEICE TRANSACTIONS on Electronics   Vol.E90-C   No.8   pp.1652-1654
Publication Date: 2007/08/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e90-c.8.1652
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Microwaves, Millimeter-Waves
ultra-wideband,  pseudo-interdigital,  stepped impedance resonators,  transmission zeros,  bandwidth,  

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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 (3-dB fractional bandwidth of 95%), low insertion loss of -0.50.4 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.