An X-band reconfigurable bandpass filter using phase change RF switches

In this paper, we report on a reconfigurable bandpass filter for X-band applications. The filter is composed of coupled X/2 microstrip line resonators. Center frequency tuning of each resonator is achieved using an RF switch based on a phase change chalcogenide compound, germanium telluride, which switches in and out a loading capacitor. A combination of electric and magnetic coupling between the resonators realizes a near constant absolute-bandwidth as the filter is tuned. The center frequency of the filter is switched between 7.45 and 8.07 GHz, with a 3-dB bandwidth of ~ 500 MHz, insertion loss of less than 3.2 dB, and return loss of better than 18 dB. The measured third-order intermodulation intercept point (IIP3) and 1-dB power compression point (P1dB) are better than 30 dBm at frequency offset of 1 kHz and 25 dBm, respectively. Measured and simulated results are in good agreement. To our best knowledge, this is the first time implementation of a tunable filter using germanium telluride based phase change switches.