Dual-mode dual-band microstrip bandpass filter with controllable center frequency

Abstract

In this letter, a dual‐mode dual‐band microstrip bandpass filter design with center frequency control methodology is presented by using dual‐mode meandered loop resonator. Center frequencies of the passbands can be controlled by changing the connection points of internally located square loop loading elements without changing the total surface area. These loading elements are also useful to obtain a compact configuration. In addition, while the first passband has two reflection zeros, the second passband has one reflection zero, as it is obtained from the harmonic of the first passband. Therefore, degenerate modes of the first passband can be excited by a perturbation element. Using patch or corner cut perturbation elements, elliptical and linear phase filtering characteristics can be obtained in the first passband, respectively. Two dual‐mode microstrip bandpass filters having elliptical and linear phase filtering characteristics were designed, fabricated, and measured. Measured results are in a very good agreement with the simulated results. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:639–642, 2015

Microstrip bandpass filters using triple‐mode circle‐shaped ring resonator with/without stub perturbation

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“…As a tuning technique, perturbation has found its advantages on S-parameter adjustment for better filter performance. Patch or corner-cut perturbation elements attached to the insides of the resonators made the elliptical and linear phase filtering characteristics accessible, generating degenerated first-passband modes 11 . In the study of Lin et al 12 , characteristics of the transmission zeros of dualmode ring resonator filters that had inductive and capacitive perturbations were investigated, and two of these zeros shifted to lower frequencies under both capacitive and inductive perturbations.…”

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