A Study of Cross Polarization Effects in Paraboloidal Antennas

摘要

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 maxium 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. 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 a formula is obtained that explains the experimentally-observed large coross-polarization. Finally, it is shown 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. (Author)