A tunable microstrip dual-mode bandpass filter based on liquid crystal technology

In this paper, a novel tunable microwave bandpass filter (BPF) based on liquid crystal (LC) technology is presented. For ease of supplying ac voltages, the proposed filter is achieved by particular configuration schemes with low cost inverted-microstrip structure. Two open-circuited stubs are placed inside a meander loop resonator so as to form quarter wavelength resonators, which is good to keep the compact configuration. By taking advantage of the property of LC, central frequency tunability is induced by applying low ac voltages. In the LC default state, the proposed filter has three-pole, it operates at 4.7GHz with about 41% fractional bandwidth (1.94GHz).