Limited Electronic Scanning with a Near-Field Cassegrainian System
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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The scanning characteristics of a near-field Cassegrainian antenna excited with a relatively small planar array are investigated theoretically and experimentally. The analysis uses both geometrical optics and scalar diffraction theory. The technique is a viable approach to the problem of modifying an existing high-resolution dish radar for limited scan capability. Feed requirements can be satisfied by virtually any planar array concept, i.e., phase scanning, frequency scanning, multiple-beam-forming networks, etc. The scan range is roughly approximated by a fixed angular field of view hence, the number of beamwidths scanned with electrically large apertures can be very high. Further, the system is free from the coma lobes usually associated with off-axis beams from a paraboloid. Design curves are presented from which one can determine the secondary characteristics - gain, scan loss, sidelobes, etc. - for a given arrayreflector configuration.
- Electrical and Electronic Equipment