Harmonic suppressed coupled stepped-impedance resonator based dual-band tunable bandpass filter

In this paper, a tunable dual-band bandpass filter (BPF) based on a varactor-loaded coupled stepped-impedance resonator is presented. Transmission matrices techniques are employed to explain the working concept of proposed tunable BPF. For validating the proposed concept, a hardware prototype is fabricated and characterized. As per the measured results, when the center frequency of the lower band is tuning from 2.15 to 2.40 GHz, the upper band is fixed at 4.5 GHz; and when the center frequency of the upper band is tuning from 4.5 to 4.75 GHz, the lower passband almost remains constant at 2.25 GHz. Proposed tunable filter is capable of working at higher passband frequencies. Spurious harmonic suppression up to 15 GHz is demonstrated. Center frequency of dual-passband is tunable using only two dc control voltages.