Forward scatter of electromagnetic waves by spheres

Experimental and theoretical studies of scattered and diffracted wave fields of reflecting spheres have been undertaken by a number of investigators in the past. The particular concern of this paper is the far-zone wave field scattered forward from such spheres, since the forward-scatter field pattern has been found to possess several interesting characteristics which have not been fully explored in previous studies. First, the forward-scatter field intensity of a sphere has the same magnitude and field pattern of a thin disc, or of a complementary circular aperture of the same dimensions as the projected area of the sphere. Second, the peak forward-scatter field intensity is considerably greater than the back-scatter intensity for a large ratio. In the case of plane wave illumination, the sphere forward-field intensity is greater by the antenna gain calculated from the equivalent aperture. This paper, in addition to describing the basic theoretical background, confirms the existence of these characteristics by actual bistatic cross-section measurements at X-band. For example, it is shown experimentalty that the peak forward-scatter cross section of a reflecting sphere is 25 db greater than its back-scatter cross section for .