Frequency tunable metallo–dielectric structure for backscattering reduction

Abstract

Electromagnetic scattering behaviour of a superstrate loaded metallo- dielectric structure based on Sierpinski carpet fractal geometry is reported. The results indicate that the frequency at which backscatter- ing is minimum can be tuned by varying the thickness of the super- strate. A reduction in backscattered power of � 44 dB is obtained simultaneously for both TE and TM polarisations of the incident field. Introduction: Reflector-backed metallo-dielectric structures have been studied extensively by many researchers for the elimination of backscattering and specular reflection (1, 2) .M ost of these structures employ metallisation based on conventional Euclidean geometries on a low-loss dielectric substrate. These surfaces find application in RCS reduction, frequency scanning reflectors and antenna design. The idea of using fractal-based metallisations in the design of metallo- dielectric structures has been reported recently in which reduction in backscattered power of � 30 dB is obtained simultaneously for TE and TM polarisations using Sierpinski carpet fractal geometry as the metallisations on the dielectric substrate (3). A fractal is a recursively generated structure that posses self-similarity and fractional dimension (4). These structures are finding wide applica- tions, especially in the design of antennas for multiband applications, due to their inherent self-similarity and space-filling properties (5) .I n this Letter, the effect of loading superstrate on a metallo-dielectric structure based on Sierpinski carpet fractal geometry is envisaged. It is found that the frequency at which reduction in backscattered power is obtained depends on the superstrate thickness. This technique can be used to reduce backscattering from a fixed metallo-dielectric structure at a desired frequency by varying the dielectric thickness of the super- strate. The frequency tuning effect is achievable for both TE and TM polarisations of the incident field. Methodology and experimental setup: The metallo-dielectric structure based on Sierpinski carpet fractal geometry is fabricated by photo- etching the metallisation on a reflector-backed low-loss dielectric substrate (er ¼ 2.56) of size 30 � 30 cm. The geometrical layout of a superstrate loaded metallo-dielectric structure is shown in Fig. 1. Fig. 2 shows the top view of the metallic structure based on the third iterated stage of the Sierpinski carpet fractal geometry used in the present work.