Compact Substrate Integrated Waveguide Tunable Filter Based on Ferroelectric Ceramics

This letter presents the design and the realization of a compact tunable filter integrated in ferroelectric ceramic substrate. The bandpass filter bases on an evanescent-mode dielectric cavity, which is loaded by a pair of tunable mushroom-type complementary split-ring resonators. Tunable impedance matching networks are additionally implemented to improve passband insertion loss across the tuning range. A prototype has been realized in a 12.5 mm × 9.5 mm × 0.8 mm planar module. Measurements confirm a frequency coverage from 2.95 to 3.57 GHz, a 3 dB fractional bandwidth below 5.4%, with an insertion loss between 3.3 dB and 2.6 dB.