A Spherical Reflector Antenna for Communication Satellite Earth Stations,
SIGNALS RESEARCH AND DEVELOPMENT ESTABLISHMENT CHRISTCHURCH (ENGLAND)
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An experimental spherical-reflector microwave antenna is described. It has a movable broad-band feed incorporating a concave subreflector, which permits plus or minus 7 degrees beam-steering without loss of gain. Overall efficiency was measured as 50, but this could be raised to 58 by eliminating reflector distortion. The first sidelobe level was -10.6dB and antenna noise temperature was 30 degrees K. Possible improvements include raising efficiency by allowing some gain variation on scanning. Optimum design then depends on system noise temperature and scanning requirements, but it is concluded that up to 75 on-axis efficiency is obtainable. Loss in gain at 7 degrees scan is typically 0.3dB.
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