Low-Noise Amplifier Design Considerations For Use in Antenna Arrays

Abstract

This work analyzes the implications of noise coupling in arrays of antennas on the design of low-noise amplifiers (LNAs). To select LNA design parameters in a manner familiar to LNA designers, the effective noise temperatures T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sup> of LNAs are presented. The effect of beamformer coefficients and antenna coupling on T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sup> is analyzed in a manner similar to a stand-alone LNA analysis. This leads to the proposed LNA design strategy of selecting LNA Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> near the reflection coefficient of antenna ports and selecting the largest practical |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | with a proper phase. This strategy is based on the assumption that the antenna array may be used for various beamforming and nonbeamforming applications, unknown at the time of the design. Numerical simulations of a 38- and 41-element antenna arrays show that a global search of LNA S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> , which result in the minimum average beam-equivalent receiver noise temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rec</sub> , finds nearly identical results to the proposed LNA design strategy. For a 41-element array with high antenna coupling at low frequencies, the proposed method shows as much as 80% improvement in the T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rec</sub> over conventional LNA design strategies that do not account for the intended use of the amplifier in an array.