Study of thin resistively loaded FSS based microwave absorbers

• Main Author: Zabri, Siti Normi
• Published: Queen's University Belfast 2015
• Subjects: 621.381
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676498

The purpose of this study was to develop new FSS based microwave absorber designs to minimise the physical thickness, increase the bandwidth and provide radar backscatter suppression that is independent of the wave polarization at large incident angles. A new low cost, accurate and rapid printing technique is employed to pattern the periodic arrays with the precise surface resistance required for each of the FSS elements to optimize the performance of this class of absorber. The electromagnetic behaviour of five new FSS based structures, two standalone arrays, and three absorber arrangements, have been studied using CST Microwave Studio software. The FSS structures consist of two closely spaced arrays of rings with the conductor split at one or two locations to provide independent control of the resonances. By careful design these are shown to exhibit coincident spectral transmission responses in the TE and TM plane. Based on this design methodology, a very thin 4-layer metal backed resistively loaded rectangular loop FSS absorber which works from 0° - 22.5° is shown to give a wide band performance that is independent of the orientation of the impinging signals. To reduce the manufacturing complexity, a single layer FSS absorber which operates at 45° incidence has been designed to give a polarisation independent performance by employing an array of rectangular split loops with discrete pairs of resistive elements of unequal value inserted at the midpoint of the four sides. A major increase in bandwidth is obtained from a single layer FSS absorber which is composed of an array of nested hexagonal loops. Moreover the use of the same surface resistance for all four elements in the unit cell is shown to significantly simplify the construction of the structure which was designed to provide radar cloaking from 0° to 45° incidence. A new manufacturing strategy is presented, where the required surface resistances are obtained by employing an ink-jet printer to simultaneously pattern the FSS elements on the substrate and digitally control the dot density of the nano silver ink and aqueous vehicle mixture.