The control of electromagnetic scattering by impedance loading

Abstract

Electromagnetic scattering from a conducting object can be controlled by loading portions of its surface with distributed or lumped impedances. The scattered field from a loaded object is expressed as a superposition of fields scattered by the unloaded object and fields reradiated by the loading. The interference of these fields can be used to produce the required scatter control. Techniques for evaluating the reradiated field are discussed. A general form for the scattered field as a function of load impedance is shown, and techniques for studying this form are discussed. Theoretical and experimental results for thin, impedance loaded dipoles are compared. For dipole lengths not much greater than λ/2, broadside backscatter can be reduced 30 to 40 dB with a passive center load. Greater lengths and other aspects require multiple passive loads. Backscatter reduction of up to 20 dB has been reported for thick dipoles at broadside incidence, planar surfaces at normal incidence, and long thin objects near end-on incidence.