A fine switching method for multibeam spherical reflector antenna design with application to full area coverage

Recently, there has been considerable interest i n spaceborne reflector antennas t o provide coverage from a few t o manybeam-widths off-axis. This i s accomplished by a sophisticated multi- element feed array. One scheme for determining the excitation coefficients for the array is described in (1). The f i r s t s t e p i n the synthesis is to calculate and plot the focal field distribution The feed array size, shape, spacing andnumber of elements are next of the reflector antenna when i t i s operating in the receiving mode. determined by examining and insuring the sampling approximates the focal field distribution (2). Once satisfactory reflector aperture illumination i s obtained, reciprocity is invoked t o cal- culate the secondary radiation patterns by using a numerical technique developed for rapid calculation of t h e f a r f i e l d pattern (3) . The reflector/array antenna is shown in Figure 1. The triangular l a t t i c e on a spherical surface is depicted i n Figures 2 and 3. Figure 2 shows the positions of a hexagon l a t t i c e f o r a scanning beam with a diamond l a t t i c e t o f i l l t h e gap i n the coverage generated by the hexagon lattices. Figure 3 demonstrates the of hexagon and diamond l a t t i c e s . possible beam positions which are realizable w i t h a combination