Zonal Reflectors

Abstract

In chapter 3, it was demonstrated that the efficiency of a Fresnel zoneplate antenna can be effectively improved by using subzone phase correcting techniques, such as the multilayer phase correction technique. However, both theoretical study and experiments showed that the sidelobe level of the zoneplate antenna tends to be high and the envelope of the sidelobes tends to be flat. Obviously, an understanding of this phenomenon is very important. This chapter is aimed to provide some insight into the sidelobe performance of Fresnel zoneplate antennas. The physical model employed as the reference is the parabolic zonal reflector, which comprises a set of confocal parabolic segments arranged along a plane surface. Within the accuracy of scalar optical theory, such a configuration should offer ideal phase correction. To model the multilayer zoneplates, the stepped zonal reflector is introduced, in which the parabolic function is replaced by a stepwise function. Since an accurate analysis of any two dimensional zonal reflector (i. e. those with a two dimensional aperture) using the method of moments (MoM) is bound to demand excessive computation power, an analysis of one dimensional zonal reflectors is carried out instead. Here, the term “one dimensional zonal reflectors” refer to those which are traditionally called “cylindrical reflectors” [16, 20].