Bandpass varactor tunable filters using step impedance resonators

A bandpass varactor tunable filter has been designed to operate from 1 to 2 GHz. In order to expand the tuning range and stabilize bandwidth, step impedance resonators with L and T coupling sections are suggested. As an illustrative example, a 2/spl times/AMP/spl times/2 order filter, tuned within 50% and having almost constant bandwidth, is reported. Integrating such a filter with a low-noise MMIC amplifier has allowed zero insertion loss to be realized.