Design and near-field measurement performance evaluation of the SeaWinds dual-beam reflector antenna

This paper presents the design and performance evaluation of a lightweight, composite material, elliptical-aperture, parabolic-reflector antenna. The performance characterization is obtained using the cylindrical near-field measurement facility at JPL. The reflector has been designed and calibrated for the SeaWinds spaceborne scatterometer instrument. The instrument operates at Ku-band and is designed to accurately measure wind speed and direction over the Earth´s ocean surface. The SeaWinds antenna design requires two linearly polarized independent beams pointed at 40´ and 46/spl deg/ from nadir. The inner beam, pointed at 40/spl deg/ from nadir, is horizontally polarized with 1.6/spl deg//spl times/1.8/spl deg/ required beamwidths in the elevation and azimuth planes, respectively. The outer beam, pointed at 46/spl deg/ from nadir, is vertically polarized with 1.4/spl deg//spl times/1.7/spl deg/ required beamwidths. Noteworthy, the reflector boresight axis is pointed at 43/spl deg/ from nadir. Both beams are required to have the first sidelobe level below -15 dB relative to the peak of the beam. The antenna was required to have a fundamental structural resonant frequency of greater than 94 Hz. To meet this requirement, it was necessary to design the struts and feed support plate size larger than nominal optimal dimensions. As expected, the increased feed-plate aperture blockage and the interaction of the feed horns with the plate resulted in higher sidelobe levels, lower antenna gain, and altered the antenna beamwidths. Careful experimental and theoretical design considerations have been found to be necessary in order to optimize the antenna design.