Enhanced imaging of reflector antenna surface distortion using microwave holography

Abstract

Two signal processing techniques are discussed that improve the accuracy of a microwave holographic measurement by removing unwanted signals from the aperture distribution: pattern simulation and subtraction, and time domain filtering. Pattern simulation and subtraction involves modeling unwanted scattering mechanisms and then removing them from the measured far‐field data. Time domain gating requires a swept frequency measurement of each far‐field point to separate undesired scattering mechanisms from the desired response. Measurements taken on a focal point geometry and a Cassegrain geometry at 11 GHz in the Ohio State University ElectroScience Laboratory Compact Range provided excellent amplitude and phase stable data to be processed by the holographic analysis system. Pattern simulation and subtraction was applied to both geometries. Surface deformation profiles generated for the Cassegrain antenna by this system were compared to an optical measurement of the main reflector surface. Good agreement was obtained. Because of system limitations, time domain filtering could not be applied.