Effects of mutual coupling on interference mitigation with a focal plane array

TLDR

A focal plane array feed of electrically small elements is proposed to achieve high sensitivity for radio astronomy in the presence of RFI, but mutual coupling becomes significant when element spacing is small relative to the wavelength. The study develops a theoretical framework to model mutual coupling and design an optimal multiport matching network for maximizing signal‑to‑noise ratio. Numerical results for a model scenario that includes spillover, amplifier thermal noise, and point signal and interference sources illustrate the framework. A suboptimal self‑impedance matching network achieves performance close to that of a full network match.

Abstract

A focal plane array feed of electrically small elements has been proposed as a means for achieving high sensitivity for radio astronomy applications in the presence of radio frequency interference (RFI). For a broadband system, mutual coupling effects become significant as the array element spacing becomes small relative to the electromagnetic wavelength. We present a theoretical framework for modeling the effects of mutual coupling and for determining the optimal multiport matching network between array elements and front-end transistor low-noise amplifiers for maximum signal-to-noise ratio (SNR). Numerical results are given for a model scenario including spillover and amplifier thermal noise and point signal and interference sources. A suboptimal self-impedance matching network yields performance close to that of a full network match.