Computation of the RCS of reflector antennas by field correlation

Describes a method of calculating the radar cross-section of single or multiple reflector antennas by means of the 'field correlation theorem' of Wood (1980). The method is based on the physical optics approximation, and enables both direct and 'indirect' scattering (i.e. scattering by an object seen in a reflector) to be calculated as a surface integral over the scatterer. A similar correlation integral accounts for blockage of one reflector by another. In the case of an axisymmetric reflector antenna, the fields set up within the antenna volume by an incident plane wave can be computed using spherical wave expansions. Using this approach, the various contributors to the RCS of typical single and dual reflector antennas can be computed. The strongest reflections in the region of the main beam come from the feed horn, which, unfortunately, is the most difficult component to model accurately. An approximate technique is described which includes the reflection due to cylindrical modes which are cut off at the throat of the horn, together with the effect of induced currents in the conducting flange.<
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