Optimisation of circular-aperture distributions for interference reduction

The directivity/noise-temperature ratio of aperture antennas, which is expressed as a ratio of two Hermitian quadratic forms, is maximised by using computer techniques. The design parameter v0 is introduced for the purpose of determining the noisefree angular region in which it is desired to confine the radiated energy. By the choice of a ficticious noise-temperature distribution, it is intended to reduce either antenna noise or interference or both. The aperture distributions that are considered are in general asymmetric and are smooth and nonsuperdirective. Symmetrical distributions that are obtained are compared with those of Taylor. Asymmetrical forms yield lower side-lobes in a prescribed noisy plane, and a slight asymmetry in the aperture distribution is shown to be enough to achieve high-interference reduction. A new class of distribution functions, which take into account the aperture blockage in the case of reflector antennas, are introduced. The effect of aperture blockage on antenna performance parameters is studied with the aid of these new distribution functions.