THINNED HEXAGONAL ARRAYS FOR SATELLITE APPLICATIONS OPTIMIZED WITH GENETIC ALGORITHMS M.C. Vigano 1 , G. Toso 1 , S. Selleri 2 , C. Mangenot 1 , P. Angeletti 1 , G. Pelosi 2 1 European Space Agency ESA ESTEC, Keplerlaan 1, PB 299, 2200 AG Noordwijk, The Netherlands, {carolina.vigano; giovanni.toso; cyril.mangenot; piero.angeletti}@esa.int 2 Department of Electronics and Telecommunications, University of Florence Via C. Lombroso 6/17, I-50134 Florence, Italy {stefano.selleri; giuseppe.pelosi}@unifi.it ABSTRACT This paper addresses the problem of the optimization of a transmit Direct Radiating Array (DRA) in Ka-band for generating a multibeam coverage from a geostationary orbit. By mean of Genetic Algorithms (GA) evolutionary optimization, more than 30% of the elements of the initial fully populated array may be switched off while maintaining the array compliant with stringent radiation constraints. INTRODUCTION Present and future generation of communication satellites will use multiple beam antennas providing down link and uplink coverages over a field of view for personal communication, direct broadcast or mobile communication applications. High gain multiple overlapping spot beams, adopting both frequency and polarization reuse, will provide the needed coverage. In order to generate high gain spot beams, electrically large antenna apertures are required. These apertures may be generated by either reflectors or phased arrays. Most of the reflector-based multiple beam antennas adopt one feed per beam architectures with adjacent beams generated by different reflectors fed by a cluster of horns [1]. This leads to three to four reflector antennas for European or CONUS coverage receive functions and the same number for transmit. A possible solution to generate a multi-beam coverage using a single aperture is the Focal Array Fed Reflector (FAFR) described in [2]. The beam generation is performed by illuminating together individual feeds using a beamforming network and the overlapped beam footprint in obtained reusing some of the reflector focal plane feeds for several beams. The FAFR is quite complex at focal array level but offers the main advantage of using only one antenna (array + reflector) to generate the full set of beams. Both the previous concepts suffer from severe accommodation or implementation difficulties. In a long term perspective, solutions based on a single aperture are more appealing and could offer important advantages especially in terms of costs, mass and spacecraft accommodation. Phased arrays would be a natural choice to generate multiple beams but they have been often dismissed essentially because of their complexity and cost [3]. One way to reduce the price of the array consists in reducing as much as possible the number of active elements (thinning the array) maintaining under control the main radiative characteristics of the array itself. 198