Design radar absorbing materials (RAMs) for wide range of angles of incidence

Usually radar absorbing materials (RAMs) for electromagnetic compatibility (EMC) applications absorb radio frequency (RF) energy at a specified rate at nearly normal angles of incidence. However, there are applications where RAM is required to perform at angles greater than 30° from normal incidence where a portion of the RF energy is scattered instead of being absorbed. This scattered energy has the potential for being a source of electromagnetic interference (EMI) to a nearby receiver. It is possible to fabricate a RAM that will maintain a minimum absorption rate over a wide range of angles of incidence. This can be accomplished by covering a base lossy dielectric slab with several matching layers. The dielectric constants of these layers are then chosen in such a way that all incoming rays. within the range of interest, are bent enough to penetrate the lossy layer close to normal incidence. This is similar to the processing used in coated lenses of photographic cameras to eliminate reflections of visible light