Contributions to the design of sub-reflectarrays

In this thesis we show how the ellipsoidal and hyperboloidal subreflectors, which are used in dual reflector antenna systems, can be emulated by reflectarrays (hereafter referred to as sub-reflectarrays). To achieve this we derive the basic design equations required to provide the proper phase correction at each element of the sub-reflectarray to end up with radiated amplitude and phase patterns that are indeed close to those of the emulated ellipsoidal or hyperboloidal subreflectors. To calculate and analyze the radiation patterns of sub-reflectarrays, which are designed based upon the above basic design equations; two analysis methods have been developed. One based on an array analysis approach which gives an approximate (yet reliable) analysis of sub-reflectarrays, with details that do not appear to have been given elsewhere. The second method is a two-dimensional (2D) full wave computational electromagnetic analysis that uses the method of moments (MoM) to solve a 2D integral equation formulation for a 2D reflectarray. It is a very rigorous method that accounts for many effects which are computationally very difficult to be include in any three-dimensional (3D) analysis methods that could be used for same purpose, like the finite ground plane effect and feed blockage effect. Both analysis methods have been validated by using them to calculate the radiation pattern of a parabolic-type reflectarray, which are frequently reported and very well known. Simulations are performed using the two analysis methods on examples of the ellipsoidal and hyperboloidal subreflectarrays described, showing the far field amplitude and phase patterns, in so doing validating the design equations and analyzing the radiation characteristics of the sub-reflectarrays. The 2D MoM analysis enables us in this thesis to study the effect of amplitude tapering upon the radiation characteristics of sub-reflectarrays. Moreover it is used to determine the location of the virtual focal point as a function of feed position and frequency, which enables us to perform a detailed study of the power focusing characteristics of an ellipsoidal sub-reflectarary. Lastly, a practical experimental validation has been done by implementing some sub-reflectarrys and measuring their radiation patterns' amplitude and phase