Cross polarization effects on antenna radiation patterns

The radiation pattern of a linearly polarized antenna excited by a linearly polarized wave is shown to be dependent in amplitude, shape, and direction upon the relative polarization of antenna and wave. The dependence of beam direction on polarization is of primary importance in practical direction-finding problems. For most orientations of antenna and wave, the azimuthal pattern peak is shown to be shifted away from the antenna boresight direction. A function is derived based on a geometrical analysis incorporating arbitrary, polarization orientations, wave elevation angle and aperture inclination. To compute the pattern shift, the function is applied to a known theoretical pattern expression. Exparimental patterns are presented which show good agreement with computed ones. Curves are given of beam shift vs the elevation angles and beamwidths of a waveguide horn polarized at 45 degrees to the vertical. A simple test far predicting a possible polarization shift for a general antenna orientation is explained.