Thin Wideband Radar Absorbers

A procedure for the optimal design of thin wideband radar absorbers is presented. The resulting absorbers are implemented by printing a frequency selective surface on a lossy perforated substrate. A binary hill climbing optimization scheme with random restart is used to find optimal solutions. The method of moments in conjunction with the transmission line method is used to calculate the fitness of structures designed by the optimizer. The optimization procedure is done in two steps in order to find a structure with best performance in terms of both operation bandwidth and angular stability. Three types of lossy substrate are considered: 1) unmodified radar absorbing substrate, 2) substrate with one circular hole per unit cell, and 3) substrate with several circular holes per unit cell. It is shown that by drilling only one hole - with optimized radius - in each unit cell, a % 100 improvement in terms of operation bandwidth may be obtained. For the case with several holes per unit cell the observed performance was not as good, which might be due to a too rough optimization.