Tunable filter based on ferroelectric films

Microwave four-pole tunable waveguide filter containing eight planar SrTiO/sub 3/ film ferroelectric capacitors is presented. The frequency tuning of the filter is due to the variation of ferroelectric capacitance with dc controlling voltage. Parameters of the filter are following: the central frequency is 27 GHz, the band width for 1 dB level is 2.7%, the range of tuning is 1.1 GHz, insertion losses are not more than 4.2 dB.