Performance of a Ferroelectric Tunable Pre-Select Filter/Low Noise Amplifier Hybrid Circuit
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ABSTRACT In this paper we discuss the performance of a proof-of-concept of a tunable band pass filter (BPF)/Low Noise Amplifier (LNA) hybrid circuit for a possible gain-compensated downconverter targeted for the next generation of K-band satellite communication systems. Electrical tunability of the filter is obtained through the nonlinear electric field dependence of the relative dielectric constant of a ferroelectric thin-film such as strontium titanate (SrTiO 3) or barium strontium titanate (Ba•Srl.,TiO 3). Experimental results show that the BPFs are tunable by more than 5%, with a bipolar biasing scheme employed. The BPF/LNA tunable hybrid circuit was used to study the effect of tuning on the hybrid circuit's performance especially on the amplifier's noise-figure and the gain. INTRODUCTION Tunable microwave components such as resonators, filters, and phase shifting elements based on the nonlinear electric field dependence of ferroelectric thin films have been recently demonstrated [1-4]. SrTiO 3 (STO), is suitable for low temperature applications below 77K, where one can reduce its relative dielectric constant by more than a factor of 5 by applying a dc electric field [4]. BaSrjTiO3. (BSTO), on the other hand, is a room temperature tunable ferroelectric, as one could reduce its relative dielectric constant by more than a factor of 3 at or near room temperature [5]. Tunabilities higher than 15% have been reported in tunable filters and resonators using both micro-strip and coplanar wave-guide transmission lines [3,6]. Recently, we have reported on K-band tunable band-pass filters using ferroelectric thin-films based on the conductor /ferroelectric/ dielectric two-layered micro-strip structure [7]. In this work, this type of ferroelectric tunable filter is integrated with a commercial K-band LNA to study the effect of tunability on the hybrid circuit's associated gain and noise-figure, for both room temperature as well as cryogenic applications. The performance of this hybrid circuit may be relevant for the implementation of a gain-compensated down converter for the next generation of satellite communication systems. DESIGN Two different filters were used in this study. One is a K-band, two-pole bandpass filter designed for 4% bandwidth, the second is a K-band, narrow-band (
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