RADIO PHYSICS AND RADIO ASTRONOMY

Subject and Purpose. Theoretical and experimental studies of an active antenna element, seen as a part of the future low-frequency radio telescope for an observatory on the lunar far-side. The project is focused on design simplification. The objective of the research is to provide for a high fl uctuational sensitivity of the telescope while minimizing antenna’s mass and dimensions, thereby facilitating its delivery and deployment on the lunar surface.

Methods and Methodology. To develop an antenna element up-scaled from the GURT prototype for 4...40 MHz, it was proposed to exclude the three-meter vertical support, using the arms of the crossed dipoles as load-bearing elements. Effectiveness was evaluated through estimating the antenna’s sensitivity, specifi cally by applying the criterion which proceeds from estimates of excess of the external over the internal noise temperature. Terrestrial experiments used short-wave radio noise as a virtual "free generator", which allowed determining characteristics of the antenna over a wide frequency range. This method enabled evaluating the antenna’s operation under actual interference conditions governed by the state of ionospheric layers D and F2.

Results. Numerical analysis and measurements showed that the proposed design, devoid of the support rack, does not significantly degrade the antenna’s sensitivity, allowing efficient reception in the 7...40 MHz range. Experiments also demonstrated possibility of operation below 7 MHz, although terrestrial effectiveness is limited by local radio interference. Under lunar conditions, where such interference is absent, additional prospects for efficient observations are open. The data confirm the antenna’s ability to follow the impact of geophysical phenomena on ionospheric parameters.

Conclusions. The results confirm effectiveness of the simplified active antenna design and suitability for lunar missions. The antenna can be employed for monitoring solar radiation and studying space radio sources in the terrestrial environment. Removal of the mast has made the modification more compact than the GURT prototype, which is critical for space transportation.

Keywords: active antenna, ionosphere, F2 layer, the Moon, radio astronomical observations

Manuscript submitted 23.12.2025

Radio phys. radio astron. 2026, 31(1): 035-050

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