An indirect holographic method for determining antenna radiation patterns and imaging antenna fields

This work describes a new technique for the determination of antenna radiation patterns and the imaging of antenna aperture fields. It uses an indirect holographic method to record simple intensity patterns formed by a combination of the antenna near field signal and an offset reference signal and is similar to methods employed at optical frequencies. This is as an alternative to the traditional direct holographic method of measuring complex amplitude and phase values. It outlines how previous practical difficulties, which have prevented this method being usefully employed at microwave frequencies, can be overcome by the synthesis of an offset reference plane wave. It describes how far field antenna radiation patterns can be obtained from knowledge of the resultant intensity pattern and how the information contained within this pattern can be further processed to provide images of the antenna aperture fields. It includes the results of mathematical simulations which strongly support the ideas outlined. Currently, an experimental system is being assembled to provide practical measurements and preliminary experimental results are expected to be available shortly.