Phased Array Antennas Scanned near Endfire

Abstract

Abstract : Excellent agreement has been shown between element patterns of circumferential and radial slots on a cone, computed with the normal mode series computer programs, and patterns measured with an experimental model with both types of slots. When the modal series is used for the computation of exact patterns, the number of modes required for convergence of the series increases as the distance of the slot location from the tip of the cone increases. Computational difficulties from accumulated round-off errors also affect the accuracy and limit the applicability of the modal series program to element positions not too far from the cone tip. The approximate asymptotic approach, on the other hand, allows the separation of the diffracted field and the geometrical optics field. More specifically, the asymptotic approach resulted in complete expressions for the E sub theta and E sub phi radiation fields in terms of optical, transition, and diffraction fields. The complete expressions for each of the two field components, in a form suitable for numerical computation, were included in the Final Report on Contract No. N00019-74-C-0127. An examination of these expressions indicates that the diffraction coefficients of both field components are only a function of the angular coordinates and not of the location of the radiating element.