Calculation of Aperture and Far-Field Distributions from Measurements in the Fresnel Zone of Large Reflector Antennas

摘要

Aperture fields and radiation patterns from Fresnel field measurements of both amplitude and phase distributions radiated by large reflector antennas were calculated. A microwave measurement system based on the concept of microwave complex holograms was introduced. Equations for the Fresnel field of a large reflector antenna on a spherical surface were derived, and the transformations necessary to calculate aperture and far fields given. The cross-polarization properties in the Fresnel zone were investigated. For small boresight angles the copolarized and cross polarized field distributions were shown to be independent of copolarized and cross polarized aperture fields respectively. It is shown that an antenna test range of about 15 times the diameter of the reflector is necessary to carry out Fresnel field measurements. Equations defining the angular test interval and the sampling distance were derived.