Novel Gaussian beam method for the rapid analysis of large reflector antennas

A relatively fast and simple method utilizing Gaussian beams (GBs) is developed which requires only a few seconds on a workstation to compute the near/far fields of electrically large reflector antennas when they are illuminated by a feed with a known radiation pattern. This GB technique is fast, because it completely avoids any numerical integration on the large reflector surface which is required in the conventional physical optics (PO) analysis of such antennas and which could take several hours on a workstation. Specifically, the known feed radiation field is represented by a set of relatively few, rotationally symmetric GBs that are launched radially out from the feed plane and with almost identical interbeam angular spacing. These GBs strike the reflector surface from where they are reflected, and also diffracted by the reflector edge; the expressions for the fields reflected and diffracted by the reflector illuminated with a general astigmatic incident GB from an arbitrary direction (but not close to grazing on the reflector) have been developed in Chou and Pathak (1997) and utilized in this work. Numerical results are presented to illustrate the versatility, accuracy, and efficiency of this GB method when it is used for analyzing general offset parabolic reflectors with a single feed or an array feed, as well as for analyzing nonparabolic reflectors such as those described by ellipsoidal and even general shaped surfaces.

I. Introduction

A FAST procedure based on a novel application of Gaussian beams (GBs) is described in this paper for predicting the near and far fields of electrically large reflectors, with slowly varying surface properties, when they are illuminated by a given feed antenna or a feed array. The conventional procedure for computing the fields of reflectors requires a numerical integration of the physical optics (PO) integral over the reflector surface; this can become computationally very slow and highly inefficient for large reflectors. Computational speed is particularly essential when performing reflector antenna synthesis wherein the reflector radiation pattern needs to be computed during each iterative step of the synthesis algorithm until the desired radiation pattern is obtained to within some prescribed bounds. Thus, in such a synthesis procedure, the numerical PO method may become nearly intractable for large reflectors. The present GB procedure for predicting the near and far fields of the reflector antenna completely avoids any time-consuming numerical PO integration on the reflector surface. As a result, the present method is extremely fast as will be demonstrated for the analysis of large reflector antennas. A wide variety of applications of this GB method are presented here to illustrate its efficiency, versatility, and accuracy by analyzing not only offset parabolic reflectors with a single feed or an array feed, but also nonparabolic reflectors made up, for example, of ellipsoidal and even more general shaped surfaces.