TABLE OF CONTENTS As pointed out previously, the design of specular RAM is equivalent to a transmission line matching problem, where the goal is to limit the reflection seen at the input caused by a short-circuit termination. The Salisbury screen and Jaumann absorbers use resistive sheets, which have only a real part to their admittance, as the matching elements. Significant flexibility can be gained in the design process if the sheets can have a susceptance as well as a conductance. This imaginary part of the admittance can be obtained by replacing the continuous resistive sheet with one whose conducting material has been deposited in appropriate geometrical patterns (e.g., dipoles, crosses, triangles), such as those shown in Figure 8.21. The term circuit analog (CA) for such absorbers is derived from the fact that the geometrical patterns are often defined in terms of their effective resistance, capacitance, and inductance; and then equivalent circuit techniques are used in the subsequent analysis and design of the resulting absorber.
A design problem closely related to that of circuit analog sheets is that of bandstop or bandpass surfaces. However, in contrast to CA RAM, such frequency-selective surfaces (FSS) do not absorb RF energy. Rather, an FSS is a frequency filter that might be employed, for example, as a bandpass radome in front of a radar antenna or as a diplexer for a dual-frequency antenna. Figure 8.22 illustrates...
