Optimization of multilayer antireflection coatings using an optimal control method

The design of a thin, lightweight, and broadband radar absorber is cast as a minimization problem of the reflection coefficient at the set of frequencies (f/sub 1/, f/sub 2/, . . ., f/sub n/) and the thickness (or surface mass) of the absorber. The authors attempt to synthesize an absorber with an undefined number of layers and assume they have the freedom to choose the permittivity and the permeability of the material in each layer from a set of specified values. A design procedure based on an optimal control method that simultaneously determines both the material properties of the different layers as well as their thicknesses, to minimize at the same time the reflection coefficient over a prescribed range of frequencies and surface mass or thickness is presented. Illustrative examples of multilayer absorbers synthesized with this method are presented, and the results are compared with those using simulated annealing. >