A Study of cross-polarization effects in paraboloidal antennas

• Main Author: Kerdemelidis, Vassilios
• Format: Others
• Published: 1966
• Online Access: https://thesis.library.caltech.edu/3738/1/Kerdemelidis_v_1966.pdf; Kerdemelidis, Vassilios (1966) A Study of cross-polarization effects in paraboloidal antennas. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3SFB-WB47. https://resolver.caltech.edu/CaltechETD:etd-09242002-083513 <https://resolver.caltech.edu/CaltechETD:etd-09242002-083513>

In this report the induced surface current method is used to investigate the spatial structure of the radiated electric field for a number of paraboloidal antennas. The paraboloids are excited by three different types of feeds, namely, a small electric dipole, an elemental plane wave source, and a rectangular horn. For the case of electric dipole excitation, formulas are derived that show the following characteristics: (i) For a reflector of constant ratio of focal length to the aperture diameter the magnitude of the cross-polarized lobe nearest to the antenna axis (paraboloid axis) remains constant relative to the maximum of the main lobe of the principally-polarized wave and is independent of the aperture size. (ii) For a given aperture size the magnitude of the cross-polarized component relative to its own principally-polarized maximum decreases with the focal length. (iii) The position of the maximum of the cross-polarized lobe depends only on the aperture size and is independent of the focal length. The problem of cross-polarization is also solved by using a simple model which gives results that are in surprisingly close agreement with those obtained by the more complete expressions. In addition this crude model explains the angular variation of the amplitude of cross-polarization component at angles not necessarily small from the paraboloid axis. For a paraboloid excited by an elemental Huyghens source the cross-polarization in the forward direction is reduced but the component in the laterally-directed radiation is increased relative to that of an electric dipole. In the case of the horn-excited paraboloid we obtain a formula that explains the experimentally-observed large crosspolarization. Finally, we show that the problems of the paraboloids excited by a small electric dipole and a plane (Huyghens) source are merely particular cases of the horn excitation problem.