Abstract
The most cited paper from this journal with “array,” “antenna,” and “noise” in its metadata is <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . While the quantitative results of that paper are correct, there is an issue with its treatment of noise received by array antennas due to noise radiation from the background (external noise). Equation (1) of that paper gives noise received by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> th array element, and the text describes the noise temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{i}$ </tex-math></inline-formula> ) in that equation as the “antenna (sky) temperature.” This should clearly be the temperature corresponding to the background noise received by the individual array elements, which includes all contributions from within the gain pattern of the individual element, which is typically much broader than the pattern of the array. However, later in the paper, this same symbol is used as the temperature corresponding to the background noise received by the array (into the receiver in Lee’s Fig. 1, after losses). These two temperatures can be very different. For example, small, individual elements of a large array could receive substantial contributions from the ground and other hot objects (e.g., at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T \sim 300$ </tex-math></inline-formula> K), while the array’s receiver only receives significant contributions from a very quiet region of the sky (e.g., at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T \sim 4$ </tex-math></inline-formula> K at some frequencies).
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