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Antenna noise temperature calculation for a reflector antenna system can be a computationally expensive operation if the structure is electrically large. Several approximate methods have been suggested to speed up the calculation. These rely on removing one or more of the reflecting surfaces from the calculation domain and compensating for the effect through geometric optics arguments. This article presents a unified multilevel approximation formalism, which allows the user the freedom to tradeoff the simulation time, implementation complexity, and result accuracy as required for a specific application. As part of the formalism, a strategy to reliably remove both reflectors in a dual-reflector system from the calculation domain and rely on ray tracing to correct the background temperature is developed. It is shown that this new method reduces calculation time by several orders of magnitude while maintaining accuracy in the final antenna temperature result of the order of 1%. It is fast and accurate enough to be used in numerical optimization loops. The method requires the implementation of a ray tracing algorithm, and thus, may present some unnecessary complexity if only rough temperature estimates are required. To this end, a simplified method is also presented requiring no ray tracing and only simple postprocessing of readily available feed pattern data. Though not as accurate as of the ray tracing-based method, temperatures may be estimated with around 10% accuracy over bandwidths well in excess of a decade. [ABSTRACT FROM AUTHOR]

Of primary importance for a radio telescope is its receiving sensitivity. The offset Gregorian reflector antennas, as used for the Square Kilometer Array (SKA) radio telescope, can be shaped to make efficient use of the reflector’s aperture and thus to maximize sensitivity for a given sidelobe level. The shape of the reflector is controlled by a mapping function. This paper presents a method to derive the optimum mapping function given a selected set of single pixel feeds. In this case, the feeds were optimized for a geometrically similar classical conic section (unshaped) reflector system. Realistic performance results are given for reflector systems with various subreflector sizes, extensions, and subtended angles. [ABSTRACT FROM PUBLISHER]

Antenna noise temperature calculations of reflector systems is often a slow process and makes direct optimization of the sensitivity of these systems a difficult and time-consuming task. This paper presents an improvement to a recently proposed method to speed up these calculations by several orders of magnitude for large dish systems. The accuracy of the improved method is tested for several types of offset Gregorian systems, and errors are shown to be in the order of a few percent. Comparisons of several layers of simplification to a standard brightness temperature model are also presented to aid the designer in the choice of model complexity to use. [ABSTRACT FROM PUBLISHER]