Contoured beam antennas may conveniently be designed by shaping the reflector surface to produce a gain pattern which closely resembles the prescribed coverage area. The most appropriate technique is based on using physical optics (PO) to calculate the far-field pattern and optimize, using a minimax scheme, the surface shape until the desired performance is obtained . For most contoured beams the gain performance is of primary importance, and so it usually suffices to employ single-reflector

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... tems which are fairly simple and thus attractive from a manufacturing and implementation point of view. However, if the antenna system is to operate in linear polarization with a stringent requirement on the polarization purity, it may be necessary to adopt polarization sensitive gridding of the reflector, or use a dual reflector configuration in which the cross polarization may be reduced by appropriately tilting the main-and sub reflector with respect to the feed. This paper presents the design of a dual offset reflector antenna for a typical European coverage divided into three regions with different gain requirements and a cross polar discrimination (XPD) constraint of 33 dB. The shaping is described in some detail and a comparison is made between designs optimized with and without XPD constraints. The coverage is shown as three polygons in Figure 1 . The relative directivity requirements are 0, -1 and -3.5 dB as indicated in the figure, and the XPD is required to be better than 33 dB in all three service areas over the frequency range 10.7-11.7 GHz. t Figure I . Definition of European coverage regions with relarive directiviry requirements indicated 0-7803-2009-3/94/$4.00 0 1994 IEEE. 894