Theoretical determination of the electromagnetic field in the neighbourhood of a parabolic cylinder antenna

A critical evaluation is made of available asymptotic methods for the determination of the near field of parabolic cylinder reflector antennas. The analysis is restricted to reflectors fed at their focus by a line current radiating an E polarisation field. Reference results, obtained in a numerically precise manner from solutions of the integral equation associated with the rigorous formulation of the radiation problem, serve as the basis of comparison of the asymptotic methods. The latter are the aperture methods, physical optics method and the Keller geometrical optics method in its original and modified forms. This study revelas that: (a) the physical optics method is accurate and reliable for medium and large size reflectors as well as for reflectors with aperture diameters as small as two wavelengths (b) the aperture methods and the modified Keller geometrical optics method are satisfactory for medium and large size reflectors (c) all of the considered asymptotic methods (excepting the Keller method in its original form) lead to results that are practically identical to those of the rigorous theory for reflectors whose diameters exceed or are equal to ten wavelengths (d) the modified Keller method constitutes the best accuracy-calculational economy trade-off for the near field analysis of the parabolic cylinder reflector antennas ordinarily encountered in microwave applications.