Novel Compact Microstrip Dual-Mode Ring Resonator Wideband Bandpass Filter with Significantly Improved Stopband Property

Peng CAI
Zhewang MA
Xuehui GUAN
Tetsuo ANADA

IEICE TRANSACTIONS on Electronics   Vol.E89-C    No.12    pp.1858-1864
Publication Date: 2006/12/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e89-c.12.1858
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Emerging Microwave Techniques)
Category: Passive Circuits/Components
dual-mode ring resonator,  transmission zeros,  wideband bandpass filter,  improved stopband,  

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A novel wideband bandpass filter with improved stopband characteristics is presented in this paper. Dual-mode square ring resonator is used in the proposed filter. New formulas based on the even- and odd-mode analysis are derived to facilitate the design of transmission zeros of the square ring resonator. A short-circuited stub and a piece of aperture-enhanced parallel-coupled lines are introduced to the input and output of the resonator to lower the passband return loss and widen the stopband of the filter significantly. The filter has a 50% fractional bandwidth, is compact in configuration, and shows remarkably improved performance compared with previously reported filters of the same kind. The measured filtering response shows a good agreement with the simulated result.