The focal region electric field distribution of an offset paraboloid

The focal region electric fields of an offset paraboloid illuminated by a linearly polarized wave incident normally on the aperture are investigated. Because of the axial asymmetrical geometry of the offset paraboloid, the axial symmetry of the magnitude of the co-polarized component of electric field is lost and the cross-polarized component of electric field is brought in the focal plane. But the offset geometry does not influence the longitudinal component of electric field. Basically, the magnitude distribution of the co-polarized component of electric field has the shape of concentric rings in the focal plane. The phase distribution of the co-polarized component of electric field on the central disk is approximately uniform in the focal plane. The variations of the electric field distribution with elevation angle and the z axis are analyzed.