Scattering from an elliptic cylinder loaded with an active or passive continuously variable surface impedance

Recently it has been shown that a plane wave reflected from an active surface may be amplified [1]. The active surface was theoretically assumed to be a corrugated planar structure with slots properly loaded with negative conductance material (e.g., Gunn, tunnel, or IMPATT diodes). If the corrugations are sufficiently close, such surfaces, whether active or passive, can be modeled in terms of an equivalent surface impedance. From the boundary-value point of view this makes the problem amenable to easy computation. In this communication, an example is discussed where a plane electromagnetic wave scatters from an elliptic cylinder loaded by a continuously variable surface impedance. For negative surface conductance, significant amplification of the backscattered field is obtained. Results are also shown for passive surface impedances.