Analysis and Design of Frequency Reconfigurable Stepped Impedance Resonator Band Pass Filter

Analysis and design of a frequency reconfigurable stepped impedance resonator (SIR) band pass filter is reported in this paper. Basic band pass filter is constructed in microstrip medium using three section interdigital stepped impedance resonators. Stepped impedance resonator plays the role for suppressing second and third harmonics and also reduces the size of the filter. Frequency reconfigurabilty of the filter is achieved by varying the electrical lengths of SIRs with help of voltage controlled varactor diodes. An equivalent circuit model of the proposed reconfigurable SIR filter is reported in this paper. Overall response of the proposed filter is computed in MATLAB using input impedance of the filter. The computed results are well matching with full wave simulation results. The electronically frequency reconfigurable filter is experimentally made and the measurements are reported. The filter is designed for a bandwidth of 300MHz and reconfigurable frequency range of 1.25GHz to 1.95GHz. The insertion loss of the reconfigurable filter over entire tuning range is less than 5.0dB and the return loss is better than 10dB. The filter is compact and measures a size of 32mmx30mmx 0.8mm. The reconfigurable filter can be intuitively used in multiband communication systems replacing traditional switched filter banks.