A wideband quasi‐millimeter‐wave bandpass filter using dual‐mode resonator with 5/4 wavelength folded stubs

A novel wideband quasi‐millimeter‐wave filter with good in‐band and out‐band performances is proposed in this article. A dual‐mode square ring resonator loaded with two 5 λ 0 /4 ( λ 0 is the center wavelength of the filter ) folded stubs is introduced to realize a 3 dB passband bandwidth of about 15% . Because of the transmission zeros produced by the dual‐mode ring resonator in the stopbands, the proposed filter exhibits sharp attenuations near the passband. On the other hand, a parallel‐coupled two‐mode resonator is introduced and integrated with the dual‐mode ring resonator to get a further improvement of the out‐band performance with wide stopbands. The fabricated filter has an insertion loss better than 2 dB in the passband and rejections greater than 20 dB at most of the frequencies in the stopbands. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1708–1711, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24457