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