Techniques for utilization of hexagonal ferrites in radar absorbers. Part 1: Broadband planar coatings

The lack of suitable materials having permeabilities (¿r) greater than unity at microwave frequencies has previously made it difficult to design thin coatings of broadband radar absorbersat this frequency range. A possible solution is to utilize the hexagonal ferrites that exhibit significant ¿rvalues (¿5) over narrow frequency bands and this paper investigates methods of deploying this material to design thin broadband microwave absorbers. Several techniques are evolved involving layering of the materials and staggering of the material electrical parametersand dimensions to achieve a good match ofthe incident waves. The computed results are substantiated by measurements of the manufacturedmaterials; measurement techniques and details of the materials used are given in appendices. It is established that a planar absorbent sheet having a reflection loss > 10 dB over 5¿20 GHz is realizable within a practically acceptable thickness.