A Ka-Band Electronically Tunable Ferroelectric Filter

This letter presents a three-pole tunable Ka-band coplanar filter that includes six high-Q BST ferroelectric capacitors. It tunes from 29 GHz up to 34 GHz (17%) with low bias voltages ranging from 0 V to 30 V. The filter has fractional bandwidths of 9.5-12.2%. It has a good insertion loss for this category of Ka-band ferroelectric filters, which is between 6.9 dB (0 V) and 2.5 dB (30 V). Two tone measurements showed that the filter has a minimum OIP3 of 15 dBm between 0 V and 30 V. The highest OIP3 value is 26 dBm achieved at a dc bias of 30 V.