Varactor-incorporated bandpass filter with reconfigurable frequency and bandwidth

We report a varactor-loaded tunable microstrip bandpass filter (BPF) with reconfigurable center frequency and bandwidth. The effects of loading varactors at intercoupled stepped-impedance resonator (SIR) resonator and at tapped input/output port coupled-lines are studied. Tuning elements are properly loaded at the middle of the coupled-line sections for achieving tunable center frequency and bandwidth performance. Initial BPF (without loading varactors) is based on a half-wavelength ((g)/2-) coupled stepped-impedance resonator (CSIR) structure. For the validation of the proposed concept, a hardware prototype is fabricated and characterized. A total of three varactors are used as the tuning elements. Only two dc control voltages are used for tuning the center frequency and bandwidth.