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Antenna designer's notebook

MEASUREMENT OF PHASE CENTER OF FEEDS In the development of a feed for a paraboloidal reflector, it is common practice to measure the amplitude and phase patterns of the feed using a model tower positioner. From these measurements, the location of the phase center of the feed can be determined using the two nomographs contributed by Tom Milligan of Martin-Marietta (Denver Aerospace). It is important to locate the phase center of a feed (that point from which it appears to be radiating spherical waves) at the focal point of a paraboloidal reflector in order to have a properly focused antenna. Also, a knowledge of the phase center location together with the measured amplitude pattern is necessary to compute the predicted secondary pattern of the antenna.