Electromagnetic Wave Scattering from an Active Corrugated Structure

Abstract

This paper studies the scattering of a plane wave by an active corrugated structure in which each slot region is connected to a microwave solid-state amplifier. Consequently, not only are we able to control the phase of the reflected wave but also its power gain. An exact solution to this problem has been obtained by the residue calculus method under the assumption that only the TEM wave propagates and is amplified in the slot region. Numerical results are presented for illustrating the scattering properties as a function of the slot dimension and the amplifier gain. An approximate but much simplified analytical expression for the reflection coefficient is derived and it should be found useful in other scattering problems (such as the design of a reflector antenna) by the ray-tracing method. A related problem of surface wave propagation on the active corrugated structure and its potential application as a high-power amplifier are also discussed.

The phase-switched screen

“…The discussion so far has considered a PSS with a single active layer that can he switched between two values of surface resistance, which are related by Equation (12). A limitation of this structure is that it can only provide a single reflectivity null with a limited bandwidth.…”

“…One possible way of improving RAM might be to make it active, i.e., to incorporate some means of changing the electrical parameters of its constituent materials. This might be done by using volumetric change, through materials such as controllable conducting polymer composites [9] or photo-dielectrics [IO], or by using discrete devices, such as semiconductor diodes [11][12][13][14][15]. Given that the same laws of physics will apply to both passive and active RAM, how can the latter improve on the former?…”

“…In principle, there is an infinite uumher of pairs of resistance values that will satisfy Equation (12). However, in the experimental PSS to he described later, the switched resistive layer takes the form of a frequency-selective surface (FSS), consisting of PZNdiode-loaded dipole elements that are biased either fully "on" or fully "off."…”

“…To simplify the discussion that follows, let r; =GI, & = G2, and 0 = 0" (the oblique-incidence case is discussed in [24]). Then, Equations (IO) and (1 1) hotb simplify to RlR2 = Zi , (12) where RI = l/Gl , R, = l/G2, andZo = l/Yo. Equation (12) has been repotted previously in connection with diode-switched reflection phase shifiers [25], hut was derived independently for 'active radar absorbers in [26].…”

Periodic structures with time-varying loads

“…(4) First the contribution from the incident electric field, E,'"", at the load location is found along with the similar incident field terms needed to solve (2) for a, and a,,. Then using the known values of a, and a,, the contribution from the scattered field is found from …”