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This paper presents a novel approach for designing planar triple-mode bandpass filters with good selectivity. The proposed triple-mode resonator is developed from traditional dual-mode stub-loaded resonator, and it is composed of a section of half-wavelength (λ/2) open-ended microstrip line and a pair of open-ended stubs. The field patterns of the three modes associated with theoretical analysis are investigated. By modifying the proposed triple-mode filter, a compact triple-mode bandpass with several transmission zeros in stopband is realized. The controllable transmission zeros provide a good selectivity to the filter. An experimental filter is fabricated, and both the simulated and measured results are presented. [ABSTRACT FROM AUTHOR]

This paper presents a dual-mode dual-band microstrip bandpass filter based on an open-loop resonant structure. By introducing a square notch and slots in the resonator, one of the passband can be controlled easily. Several finite transmission zeros are realized to improve the selectivity of the proposed dual-band filter and the isolation between the two passbands. To verify the proposed filter, an experimental filter is implemented. Both the simulated and measured results are presented. [ABSTRACT FROM AUTHOR]

A microstrip bandpass filter implemented with slow-wave open-loop resonators is described in this letter. The slow-wave open-loop resonators make the filter compact and allow implementation of positive and negative inter-resonator couplings. Implementation of the positive and negative couplings is used to introduce a pair of finite frequency transmission-zeros in the filter response. The two zeros are designed to be close to the passband, thus improving the selectivity of the filter. As an example, a quasi-elliptic filter is fabricated. The quasi-elliptic filter has a compact dimension of 22.1 mm × 21.16 mm, which is approximately 0.1705λg × 0.1634λg. The experimental results are demonstrated and discussed. [ABSTRACT FROM AUTHOR]

A novel planar microstrip triple-mode bandpass filter is proposed by introducing slits into λ/2 traditional microstrip resonator in this article.The slits cannot only perturb the traditional resonator for the multimode operation but also generate transmission zero point at stopband for the stopband control. By using different kinds of slits, different kinds of responses triple-mode bandpass filter can be realized. For method validation, a filter operating at 2.45 GHz is fabricated and measured. Both the simulated results and the measured results are presented. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1260-1262, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25965 [ABSTRACT FROM AUTHOR]