Improved accuracy in the PO analysis of reflectors with non-perfectly conducting surfaces

For the investigation of reflector antenna systems it is custom to assume that the reflectors are perfectly electric conducting (PEC). This assumption allows the use of the standard physical optics (PO) method in the analysis of the radiation pattern from the reflector antenna, and PO is the most widely used method for this kind of analysis. However, for many modern antennas, the assumption of perfect conductivity is not valid. It has been found that in some reflector configurations the uniform plane-wave approximation is too crude to achieve sufficiently accurate results. The problem especially shows up on the rear side of the reflector, where the PO scattered field should be added to the incident field to obtain the total field. High accuracy of the PO field is required to have a proper addition of the fields. In this paper, a solution to this problem is presented. Higher-order contributions are derived which should be added to the extended PO method. The higher-order contributions are proportional to the slope of the incident field.