Depolarisation effects of metal-space-frame radomes

The spread of commercial satellite communications into geographical regions where adverse weather conditions can affect circuit availability, together with the movement to higher-frequency bands, where the effects of weather are more significant, has caused a resurgence of interest in large metal-space-frame radomes. The electrical performance of the earth-station antenna is modified by the presence of the radome, and the resultant crosspolarisation component within the tracking accuracy of the antenna is of particular interest. The paper describes an analytic method for determining the depolarisation effects of a metal-space-frame radome enclosing a typical earth-station antenna. The analysis has been based on the induced-field-ratio (IFR) hypothesis for struts having either a circular or rectangular cross-section. Incident circular polarisation has been assumed throughout, although the analysis is applicable to linear as well. An experimental programme has also been performed to validate the predictions.