Center Frequency and Bandwidth Tunable Filter Employing Tunable Comb-Shaped Transmission Line Resonators and J-inverters

This paper presents a novel and simple-structured digital tunable bandpass filter that individually controls the center frequency and bandwidth. The filter consists of tunable lambda/4-length resonators and tunable J-inverters. The employed tunable resonator has a transmission line with a comb-shaped pattern on both sides of the line and multiple switches placed between the teeth of the comb-shaped pattern. The tunable J-inverter comprises a microstrip gap having multiple conductor tips and switches in the gap. A prototype two-pole tunable bandpass filter is designed and fabricated to verify the feasibility of the proposed filter. The tuning ratios of the measured bandwidth and center frequency are 2.67 and 1.14, respectively