Beam scanning performance of active-feed reflectarray antennas are studied in this paper. The advantages of active-feed systems for high-gain beam scanning are delineated and bifocal reflectarray systems are investigated. It is shown that a conventional bifocal reflectarray cannot achieve a good performance over a wide angular range. The particle swarm optimization is then implemented to optimize the phase of the bifocal reflectarray system. A Ka-band reflectarray antenna designed for 60° beam scan and optimized for two beams at ±30° is demonstrated. Within the scanning range, the gain variation is smaller than 1.6 dB and the side lobe is lower than -15 dB.
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