8.1 INTRODUCTION

Although shaping is the first line of RCSR and can provide dramatic reductions in signature over limited aspect angles, many situations require absorption of the incident electromagnetic energy, if design goals are to be achieved. Therefore, a knowledge of the design and application of radar absorbing materials is vital to the engineer whose task is to minimize the radar signature of a vehicle.

As discussed in Chapter 6, basic scattering phenomena may be broken down into specular and nonspecular mechanisms. As might be expected, RAM design must also be approached with consideration for the scattering mechanism of interest. Accordingly, in this chapter, RAM design and performance will first be discussed with reference to specular reflections. Then, the design performance of nonspecular RAM will be considered.

The electromagnetic aspects of RAM design focus principally on the synthesis of an arrangement of dielectric or magnetic materials that provide a specified impedance profile to an incident wave. A study of the evolution of RAM design is a study of the materials and techniques employed to achieve desirable impedance properties (and, hence, good absorptive qualities) over ever increasing bandwidths. In organizing the chapter, the basic theory underlying specular RAM design is first considered, and analytical design methods are presented. Then, the design methods are used to illustrate the types of structures typical of current RAM implementations and the performance that can be achieved in those implementations.

A study of the physics of electromagnetic wave absorption should begin with the microscopic or...