An Active Ribbon Dipole as an Array Element Prototype for the Lunar Very Low Frequency Radio Telescope

This work is concerned with a detailed study of an active antenna, which can serve as a prototype of a phased array antenna element for a future lunar very-low-frequency (VLF) radio telescope operating in the frequency range of 1-30 MHz. The antenna consisted of a ribbon symmetrical dipole and a low-noise preamplifier. A dipole 10 m long lay on a flat surface of lunar soil, consisting of a layer of regolith 10 m thick and solid bedrock. The dipole parameters were determined by full-wave simulation using the Altair Feko 2022 software. The preamplifier was a single-stage HEMT low-noise amplifier, whose parameters were determined using the Advanced Design System 2023 software. An active antenna was analyzed using a model created to calculate all electrical and noise parameters. Special attention was paid to the analysis of the antenna sensitivity in terms of the System Equivalent Flux Density (SEFD) and Sky Noise Dominance (SND), taking into account changes in the lunar ambient temperature from 100 K to 400 K. It was shown that the frequency dependences of many active antenna parameters, in particular, radiation efficiency, directivity, effective area, SND, and SEFD had noticeable oscillatory components. The radiation pattern of the antenna was also subject to cyclical changes that occur in sync with the changes in directivity. These properties of the active antenna, caused by the presence of two-layer soil, should be considered when developing future lunar VLF radio telescopes.