Aperture Antennas and Diffraction Theory

PBEW010E * 9780906048528

Two powerful techniques for the analysis of aperture antennas
are now used. One is based on the convenient Fourier transform
relationship between aperture field and far-field radiation
pattern. Here this relationship is derived from the plane wave
spectrum representation of the aperture fields. In the near field
of the aperture, Fourier transforms become Fresnel transforms.
Far-field patterns may be predicted from near-field measurements by
treating the near field as the aperture plane. In its application
this method is basically the Kirchhoff approximation of diffraction
theory. It is accurate for the forward fields of large antennas but
cannot provide the lateral and back radiation. The other method is
based on aperture edge diffraction and called the geometrical
theory of diffraction. It is developed from an asymptotic
approximation to rigorous diffraction theory. Inherently more
accurate and more widely applicable, it is especially useful in the
calculation of antenna radiation in the lateral and rear
directions. However, at present it fails in some situations where
the Kirchhoff method succeeds, for example the axial fields of
paraboloidal reflectors. In this sense the two methods are
complementary and often both are required in antenna analysis.
Application of the two methods to the calculation of the pattern,
gain and reflection coefficient of some common antenna types is
shown and comparisons are made with experiment.

Author

E. V. Jull