Phase-only reflector antenna metrology

Abstract

The measurement of reflector antenna surface profiles using a phase-only metrology technique is presented. By measuring the near-field phase of a pencil beam antenna and the use of a suitable algorithm, deviations from the desired reflector aperture phase can be related to distortions on the reflector surface. By a suitable choice of measurement wavelength, quite high accuracies can be achieved. Experiments using a wavelength of 8.5 mm have shown that surface deviations as small as 0.1 mm can be detected. Two experimental techniques for obtaining this near-field phase data have been investigated. One uses a conventional plane-polar near-field measurement range employing electromagnetic waves at 35 GHz. The other uses a linear array of ultrasonic receivers operating at 40 kHz, again in a plane-polar measurement configuration. In this latter case the radial part of the plane-polar scan is performed electronically using the linear array, providing a very rapid scanning system. Both systems have been built and tested using a 1.2 m diameter parabolic reflector antenna whose surface profile has been accurately measured using a 3-axis computer controlled mechanical measurement machine. Very good agreement between this profile and those measured using the phase only metrology method are demonstrated.