A 6.2–7.5 GHz tunable bandpass filter with integrated Barium Strontium Titanate (BST) interdigitated varactors utilizing silver/copper metallization

A 3rd-order combline tunable filter is implemented utilizing ferroelectric Barium Strontium Titanate (BST) interdigitated varactors. The filter and its varactors are integrated on a ceramic substrate using a simple resistive biasing circuit. Upon the application of a bias voltage ranging from 0 to 40 V the passband of the filter tuned from 6.2 to 7.5 GHz while maintaining a fractional bandwidth of approximately 13.8 %. Over the tuning band the passband insertion loss varied from 8.5 dB to 6.3 dB while the return loss was better than 10 dB.