An extended aperture integration method for reflector antennas

In recent years, a variety of techniques have been proposed to analyze the reflector antennas. Among these techniques, the aperture field integration and the physical optics current methods have been used extensively and attempts are made to determine the range of their validity and computation accuracy. For instance, Yaghjian [l] has shown that the far fields of reflector antennas determined by the physical optics currents are identical to those of the geometrical optics aperture integration method, when the aperture surface caps the reflector. The physical optics method involves complicated current integrations over the reflector surface and it is, generally, easier to use the aperture integration approach. However, if the aperture plane caps the reflector, the feed lies outside the region between the reflector and the aperture plane. Thus, in determining the reflector far field, the feed radiation pattern can not be used in the aperture field calculations. Yaghjian has suggested that the incident field of the feed may be neglected, which limits the validity and the accuracy of the method. The accuracy of both physical optics current and the geometrical optics aperture field methods is normally acceptable in calculating the main beam and the iirst few sidelobes. To calculate the far out sidelobes or to improve the accuracy of the results for the main beam and near-in sidelobes, Rahmat-Samii [2] has shown that the fringe currents should be included in the current integration and the edge diffracted fields in the aperture field integration method. The latter requirment means that the selected aperture size must be large enough to intercept the main or significant diffracted rays. Since the diffracted rays are strong along the reflection boundary and decrease in magnitude thereafter, an arbitrary angle of 4Y at the reflector edge may be selected to define the aperture boundary, Fig. (1). The aperture size will, therefore, depend on its separation distance from the reflector edge. However, to reduce the computation time it is desirable to reduce the aperture size. The requried aperture size is minimum when it caps the reflector. In the present work it is selected to be at a short distance (0.l~) in front of the reflector edge. It therefore falls between the feed and the reflector. To include the