Three analysis methods for reflector antennas, the spherical near-field geometric theory of diffraction (SNFGTD), the moment method (MM) and physical optics (PO) are compared. In the SNFGTD method, the far field from the antenna is found by a spherical near-field transformation (SNF) of the tangential electric near field on a sphere surrounding the antenna once this has been found using the geometrical theory of diffraction (GTD). SNFGTD and MM agree very well, whereas PO differs with respect to the cross-polar pattern. Some discrepancies between SNFGTD and MM are shown to be related to inaccuracies in the GTD diffraction coefficients close to the reflection boundary.

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A mechanically controllable reflector has been manufactured by using an electroformed Nickel shell supported and controlled by 19 actuators. If such a system is used as subreflector in a millimetre-wave antenna system for limb-sounding applications, it is possible to reduce the accuracy requirements to the main reflector and thereby save on overall costs. Instead, the shape of the subreflector is controlled to correct for the thermally induced deformations on the main reflector. The paper describes the method of generating the desired subreflector shape for given distortions, and the experimental model that is used to demonstrate the feasibility of the technique.