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 ef f of LNAs are presented. The effect of beamformer coefficients and antenna coupling on T ef f is analyzed in a manner similar to a stand-alone LNA analysis. This leads to the proposed LNA design strategy of selecting LNA Γopt near the reflection coefficient of antenna ports and selecting the largest practical |S11| 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 S11 and Γopt, which result in the minimum average beamequivalent receiver noise temperature Trec, 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 Trec over conventional LNA design strategies that do not account for the intended use of the amplifier in an array.

Noise Temperature of Phased Array Radio Telescope: The Murchison Widefield Array and the Engineering Development Array

“…Effectively, both the previously mentioned voltage and power framework works by computing a similar ratio described by (1). The proposed framework for calculating T rcv using [15] was shown to be consistent with current methods in [17] when compared to the voltage and power framework found in [1], [3]. (1) The LNA was slightly modified to have a larger bandwidth (50-300 MHz).…”

“…While not shown, (11) and (5) produces identical results to formulations found in [3] for the computation of incident noise power and transducer gain (3) .…”

“…However, there are many frameworks for computing it. For example, the computation of T rcv using a voltage framework was demonstrated in [1], while other power based methods are covered in [2] and [3] which involves the calculation of available gain of the phased array. For radiation efficiency calculation, power based frameworks were demonstrated in [4]- [6].…”

Cold-Source Noise Measurement of a Differential Input Single-Ended Output Low-Noise Amplifier Connected to a Low-Frequency Radio Astronomy Antenna

“…The immediate context of this paper is noise temperature of a single DISO LNA connected to one antenna. Hence, noise coupling that occurs in a low-frequency radio astronomy arrays [23], [24] is not reflected in the results. However, the direct measurement method we discuss may be applied to an antenna array if it is placed in a sufficiently large anechoic chamber.…”

Improved Decoupling for Low Frequency MRI Arrays Using Non-Conventional Preamplifier Impedance

“…We show that if the achieved preamplifier decoupling is high enough, then each array element will have an impedance similar to the impedance of a single element in isolation, which is beneficial in terms of individual SNR of each element. Previous studies have shown that even in a high coupling situation, the combined SNR of the array is not degraded if full knowledge of the complex coupling coefficients can be obtained to calculate the optimal weights for the combination [6]- [8]. However, in the more general case where the weighting factors are not known a-priori, the method proposed here facilitates improved noise matching of each coil element, and also the subsequent image combination.…”