Center frequency and bandwidth tunable compact SIR bandpass filter

This article describes a tunable SIR (Stepped-Impedance Resonator) filter using varactor diodes with tuning range from 2.2 GHz to 3.2 GHz. An analytical and progressive approach has been adopted. The simple addition of line sections at the end of the resonators of the reference structure validated the principle of the center frequency and bandwidth tuning. The use of varactor diodes as tuning elements allows continuous and independent control of these parameters. A bandwidth tunable filter, which is being manufactured, was simulated and the simulated results showed that the -3 dB relative bandwidth varies from 44% to 16% with a fixed center frequency at 2.7 GHz.