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ABSTRACT This article proposes a novel type of microstrip cascaded triplet filter with controllable electric and magnetic coupling. The electric coupling can be tuned by adjusting the gap between the resonators, while the magnetic coupling is dominated by the diameter of the via-hole. A transmission zero on the upper stopband is produced by the inductive cross-coupling. To further improve the selectivity of the filter, the source-load coupling is also proposed to introduce two tunable transmission zeros. To expand the stopband, proper feeding position is selected to suppress the third and fifth harmonics. Based on the proposed structure, a third-order filter are designed and fabricated. Good agreement between the measured and simulated data is obtained. Measured results indicate that a rejection level of 20 dB up to more than six times the passband frequency can be obtained. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2937-2940, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT Compact microstrip triband bandpass filters are proposed and designed based on asymmetrically loaded resonators in this letter. By attaching single open-circuited stub or short-circuited stub at the proper position of the microstrip line and adjusting their lengths, the first three resonant modes of the proposed resonators can be usefully allocated within the three passbands of the triband filter. Two alternative triband filters with compact size are designed and measured. The measured results provide successful verification for the theoretical analysis. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1862-1865, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT Tri-band bandpass filter using centrally loaded resonators is presented in this article. The triple-passband characteristics are realized by properly controlling the lengths and impedances of the uniform impedance resonator and the stub. To illustrate the concept, two tri-band filters are designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. The prototype of the tri-band filters achieve insertion loss of 1.6, 1.9, and 1.9 dB at 2.4, 3.5, 5.8 GHz, 1.2, 1.3, and 1.3 dB at 1.57, 2.45, 5.2 GHz, respectively. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2695-2699, 2013 [ABSTRACT FROM AUTHOR]