K. Balasubramanya

Abstract: A multipole expansion technique to study radiation from aperture antennas in the form of an open-ended waveguide-horn is presented. Particular attention is paid to dual-mode and corrugated circular horns. The radiation pattern of these feeds, derived in terms of multipole moments, is in the form of an algebraic series which converges very rapidly. Further, based on the multipole-expansion technique presented, the far-zone fields of an axially-symmetric aperture-fed paraboloid are obtained in closed form. It is demonstrated that there is a drastic reduction in computer time by using this technique instead of the conventional numerical integration procedure for calculating the far-zone fields of the paraboloid.

Abstract: An equivalent network for square and rectangular shaped microstrip radiating elements is derived. In order to simplify the problem the radiating element is considered as two slots separated by a transmission line of low characteristic impedance. The slots are characterized by their radiation pattern, directivity, and equivalent admittance. A design procedure for open circuit halfwave resonators and for arrays of such resonators is given. Finally, some antennas in the X band are designed and measured.

Abstract: The uniform geometrical theory of diffraction (UGTD) has been applied successfully to analyze the near-field patterns of a prime-focus paraboloid. In order to establish the validity of the analysis, near-field amplitude and phase patterns have been computed over the principal planes at several observation distances for a typical prime-focus paraboloid. These calculations compare very favorably with the corresponding results obtained numerically with the aid of Silver's near-field aperture integration formula.

Abstract: A multipole expansion technqiue is developed for calculating the co-polar and cross-polar radiation patterns of a prime-focus paraboloid fed by a dominant-mode rectangular waveguide feed. Initially, the feed radiation pattern is expressed in terms of electric and magnetic multipoles of different orders which are subsequently used to obtain the secondary radiation patterns (co-polar and cross-polar) in explicit closed form in the form of a rapid by a converging algebraic series. The validity of the analysis is effectively demonstrated by calculating the co-polar and cross-polar patterns of a typical paraboloid and comparing and results with calculations based on the direct numerical integration of the physical optics currents induced on the reflector surface.