Voltage-controlled RF filters employing thin-film barium-strontium-titanate tunable capacitors

Tunable lowpass and bandpass lumped-element filters employing barium-strontium-titanate (BST)-based capacitors are presented. A new metallization technique is used, which improves the quality factor of the tunable BST capacitors by a factor of two. The lowpass filter has an insertion loss of 2 dB and a tunability of 40% (120-170 MHz) with the application of 0-9 V DC bias. The bandpass filter (BPF) has an insertion loss of 3 dB and a tunability of 57% (176-276 MHz) with the application of 0-6 V DC. The third-order intercept point of the BPF was measured to be 19 dBm with the application of two tones around 170 MHz.