Tunable dual-mode bandpass filter based on liquid crystal technology

In the last years, there has been an increasing interest in using liquid crystals for designing tunable devices at microwave frequencies due to the anisotropy of the LC physical properties. In this paper, the design, simulation and characterization of a voltage-controlled bandpass filter based on LC technology is presented. A microstrip square patch resonator with a dual-mode operation is proposed as the bandpass filter because of the advantages of using dual-mode technology, specifically in size reduction. A filter central frequency variation from 4.54 GHz to 5.19 GHz is measured when an external AC voltage is applied, which means a relative tuning range of 13.4%.