Abstract
A method is presented for the computation of the far field radiation patterns of paraboloid reflector antennas by using a modified stationary phase approximation to eliminate one integration. This method is applicable to open cassegrain, offset paraboloid and horn reflector antennas. For symmetrical paraboloid antennas the modified approximation reduces to the exact expression obtained by direct integration. The errors introduced by the stationary phase and modified stationary phase approximations are investigated. Specifically the far field of an open cassegrain with a 128 wavelength aperture diameter is computed by the approximate method up to 20 degrees off-axis. The difference between these radiation patterns and those computed by double integration, is less than a few tenths of a dB up to 1.0 degree, and less than a few hundredths of a dB at larger angles off-axis. In order to estimate the computational advantage of this approximation, the number of points required for integration of an oscillatory function by Simpson's rule is also examined and it is determined that at least 6 points per cycle are necessary to obtain 4 decimal accuracy. For fewer points the error is appreciable.
Published Version
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