A 2.2 – 3.4 GHz Constant Bandwidth High-Selectivity Tunable Filter Based on Dual-Mode SIW Resonators

This work presents a tunable, high-selectivity bandpass filter with constant absolute bandwidth. The proposed design utilizes two dual-mode, substrate-integrated-waveguide cavity resonators to create a second order bandpass response with a transmission zero on each side of the passband. Each dual-mode resonator is tuned using one contactless tuner that controls both modes simultaneously in order to maintain constant absolute bandwidth. Therefore, the structure has the same size and number of tuners as a conventional second order bandpass filter. The filter center frequency is tunable from 2.2 - 3.4 GHz and the 3-dB absolute bandwidth is 130±1 MHz over the tuning range. The filter exhibits an insertion loss better than 1.36 dB, and the rejection of the transmission zeros is better than 25 dB. Compared to state-of-the-art filters, this filter maintains a constant bandwidth over the widest tuning range while exhibiting low loss and without requiring additional tuning elements.