Co-polar and cross-polar diffraction images in the focal plane of paraboloidal reflectors: A comparison between linear and circular polarization

Equations for the co-polar and cross-polar fields in the focal plane of paraboloidal reflectors when excited by a plane wave are derived for linear and circular polarization, it is shown that for linear polarization the co-polar diffraction image consists of an elliptically shaped bright region followed by dark and bright zones. On the other hand, the cross-polar image consists essentially of four bright spots separated by a dark cross. These theoretical findings were confirmed by measurements. With circular polarization the co-polar diffraction image comprises a bright central circle followed by dark and bright rings, whereas the cross-polar image consists of a dark central circle followed by bright and dark rings. It is also shown that the field distribution in the image space is affected to a great extent by the angular semiaperture
\psi
'. Graphs of the variation of the image characteristics with
\psi
are also given.