Tune-all microstrip bandpass filter

A compact, varactor-incorporated microstrip bandpass filter of controllable center frequency and bandwidth, as well as reconfigurable response is presented. The quasi-lumped dual-mode resonator is adopted for filter compactness, and the incorporated varactors are employed for resonance perturbation and mode coupling control pertinent to frequency agility. Compared to the authors´ previous design, the electrical size is significantly reduced (4 times smaller), and the largest to smallest bandwidth ratio (6:1) is greatly extended.