An alternative application to tune the center frequency of a microstrip balun bandpass filter

Abstract

In this paper, a novel microstrip balun bandpass filter with tunable center frequency is presented. The proposed structure is constructed by open loop resonators having varactor diodes. The varactor diodes are used to tune the resonant frequency of the resonators. By virtue of coupled open loop resonators with varactor diodes, two bandpass filters in different filtering characteristics are designed at same center frequencies. Those filters can also operate in a range of 1.8-2.2 GHz depending on the changes in the capacitances of varactor diodes. The proposed balun bandpass filter is carried out using the presented filters. For demonstration, the proposed circuit was fabricated and tested. Experimental results exhibit an acceptable agreement with the estimated results. © 2019 EuMCE.