Limited Electronic Scanning with an Offset-Feed Near-Field Gregorian System
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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The scanning characteristics of an offset-feed near-field Gregorian antenna excited with a planar array are investigated. The analysis is based on the assumption that the fields in the near-zone region of the array can be accurately determined by the methods of ray optics, i.e., geometrical propagation along ray trajectories. Scalar diffraction theory is used to compute secondary characteristics. For one example considered, a 12 degree beam is scanned over a cone with a half angle of approximately 7 degrees as defined by the -3-dB scan-loss criterion. The effects of changing parameters - magnification, reflector sizes, frequency, etc. - on the scan characteristics are discussed. An experiment which was performed to demonstrate the technique is described.
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