Ferroelectric Tunable Bandpass Filters for Ka-Band Applications

This paper presents two 3-pole tunable bandpass coplanar filters that include BST ferroelectric capacitors, tunable from 28 GHz up to 37 GHz. Both filters consist of cascaded coplanar transmission resonators, loaded with high-quality factor discrete BST capacitors. The first design includes 6 capacitors and the second one is loaded with 12 capacitors. The capacitance is varied from 60 fF up to 20 fF. A first fabrication was done only with fixed capacitances, in order to validate the model. The insertion loss was around 5 dB at 30 GHz.