An Analysis of Thermal Characteristics of the Dish of a 25m Radio Antenna Based on the ASHRAE Clear-Sky Model

Deformation of the dish of a radio antenna due to longtime sunshine can severely affect the pointing accuracy of the antenna. A key problem for understanding antenna thermal deformation is to determine temperature distributions on the dish surface. Calculations of temperature distributions on a dish surface are not easy, as a time-dependent direction to the sun and the screening of sunlight by the dish itself need to be taken into account. In this paper we present our results of numerical simulations of temperature distributions on the dish surface of a 25m radio antenna based on the ASHRAE clear-sky model. Our simulations incorporate the iterative-regression formula of coefficients from the Beijing clear-sky model. In the simulations we mainly consider three factors in June 21st, which are the change of sunlight irradiation on the dish surface, convectional heat exchange with ambient air, and environmental long-wavelength radiation. The simulations were carried out using the ANSYS software package for finite-element modeling. We finally present variations of antenna temperatures, which should be helpful for better understanding thermal deformation of the dish of a radio antenna and effective calibration of antenna pointing.