Tunable Ferroelectric Filters for Software Defined Tactical Radios

Tunable filters are critical size, weight, power, and cost (SWAP-C) enabling components for military radios: joint tactical radios (JTRS), weapons data link (WDL), tactical target networking technology (TTNT), and cognitive radios. The ability to tune (center frequency, bandwidth) and reconfigure (bandpass, notch) filters dynamically in the system allows agile communications. In this paper we will present experimental results on tunable radio frequency (RF) filters using low loss thin film high dielectric constant barium strontium titanate (BST) ceramics. The circuit design, simulation, and experimental results on 2-pole and 3-pole lumped circuit filters will be presented from VHF to L-band frequency ranges. Results will be shown on three tunable filters: 137-225 MHz, 450-750 MHz, and 1500-2000 MHz. These filters met all the critical performance specifications such as insertion loss < 3 dB, return loss < -15 dB, frequency tunability of 1.7:1, and input intercept point of +35 dBm for an operating bias voltage of 0-10V DC. These filters also exhibited the following features compared to PIN diode switched capacitor filters: Parts count reduction: 3X, area reduction: 4X, power reduction: > 10X, and assembly/tuning labor reduction: >>10X.