On the Evaluation of Image Region Fields for Dual Reflector Scanning Antennas

Evaluation of the field from dual reflector scanning antennas using the physical optics approximation is impractical when the main reflector is large. Asymptotically evaluating the physical optics integral yields the geometrical optics field as the first term in the solution. This approximation is not always sufficient as it does not account for diffraction. The next higher order term in the asymptotic expansion yields diffraction effects. This is compared with the geometrical theory of diffraction (GTD). These methods are applied to a practical dual reflector scanning antenna. It is shown that the physical optics and GTD approaches are complementary allowing rapid evaluation of the field.