Tunable IF Filter using Thin-Film BST Varactors

This paper describes the design and characterization of a lumped-element tunable IF filter using thin-film barium strontium titanate (BST) varactors. The filter was designed to operate from 30-88MHz in three separate switch-selectable bands with a 0-12V DC control voltage. A relatively constant insertion loss of <5dB was obtained over the desired tuning range. The circuit was also characterized over temperature from -40degC to +80degC, showing relatively little change in insertion loss over temperature, but a slight reduction in tuning range at elevated temperatures.