Fully Reconfigurable Bandpass with Continuously Tunable Center Frequency and Bandwidth Featuring a Constant Filter Characteristic

This work presents a reconfigurable microstrip bandpass filter with fully controllable external, inter-resonator couplings and resonators. This enables an independent tunable center frequency and bandwidth, featuring a constant filter characteristic over the entire tuning range. A cross-coupling is used to introduce a symmetric pair of transmission zeros to increase the selectivity. The resonance frequency of each split-ring resonator can be tuned by varactors, which increase the electrical length by providing additional capacitance. The couplings between the resonators are influenced by additional varactors to tune the bandwidth. The presented filter is designed for a center frequency tuning range from 1.535 GHz to 1.755 GHz with a constant absolute bandwidth, which results in a center frequency tunability of 12.5 %. The bandwidth tuning peaks at 1.7 GHz with a range between 60MHz to 138MHz.