TABLE OF CONTENTS Historically, absorbers have been materials added to a structure after the mechanical design was sized to carry the required loads, with the absorber included as a parasitic element. The underlying assumption was that the RAM would have no significant structural properties of its own. The spreading use of composites as structural materials in a number of types of platforms has increased the interest in the design of RAM as an integral part of the structure or, in some cases, as the primary load-bearing member. Particularly in the aviation community, the move toward composites as structural materials has not been driven by RCS requirements. Instead, composites (both metallic and nonmetallic) have generally been employed where they offer weight savings over conventional structures. Therefore, it is of interest to consider how radar absorbing properties might be integrated into composite structures.
Concurrently, work has been done in combining RAM types (e.g., magnetic and circuit analog, or Jaumann and graded dielectric) to provide broader bandwidths in thinner packages or improved performance within the same band for the same RAM thickness. Materials that combine two or more of the basic absorber designs are called hybrid RAMs. Although not all of the work on hybrid RAM is related to radar absorbing structures (RAS), the two areas have been closely enough related that they can be logically grouped for discussion.
The major thrust in RAM for military applications has been toward the...
