Comparison of ferrolectric and varactor tunable filters controlled by DAC

Development of microwave technologies (especially GSM, Wi-Fi and LTE) and UHF receivers (tactical and cognitive radios) offer us realization of very compact and high performance tunable filters. In this paper, narrow band semiconductor and ferroelectric lumped bandpass tunable filters have been designed with the same topology and their fabrication outputs were derived. Varactor diodes and Barium Strontium Titanate (BST) capacitors are used as tuning element in this work. After theoretical analysis, the filter has been constructed and evaluated in ADS (Advanced Design System) simulation software. S parameters of filters have been derived from both simulation results and fabrication output. Center frequencies of filters vary from 382 MHz to 604 MHz (0.65 octave) with approximately constant fractional bandwith. Insertion loss alters from 3.1 dB to 8.2 dB. Performances of Varactor Diode and BST capacitors have been compared and showed. 60 V pin selectable Digital to Analog (DAC) converters with 12 bit resolution are used to drive of these capacitors.