Affiliated with the
Communication & Space
Sciences Laboratory

Fractal Antenna Engineering

Fractal Frequency Selective Surfaces

Stage 3 Crossbar Fractal Tree FSS Elements

Members of CEARL have developed techniques for the design of multiband Frequency Selective Surfaces (FSSs) that are based on the use of fractal screen elements. We demonstrate the design methodology by exploiting the self-similarity of the crossbar fractal to implement a tri-band FSS. Another benefit of this design approach, in addition to its multiband performance, is that the frequency response of both the TE and TM modes are exactly the same, owing to the symmetry in the tree-like fractal structure of the screen elements. Dielectric loading effects have been considered for practical implementation of designs with coverage exceeding two bands. Finally, it is noted that the locations of the individual bands can be controlled by the scaling or similarity factor used in the construction of the fractal screen elements.

..: References :..

1-) Planar Multiband Infrared Metallodielectric Photonic Crystals

2-) Multiband Planar Metallodielectric Photonic Crystals Using Frequency Selective Surface Techniques
by R. P. Drupp, J. A. Bossard, D. H. Werner, and T. S. Mayer
2004 IEEE International Symposium on Antennas and Propagation, Monterey, California, June 20-26.

ABSTRACT: Two-dimensional single layer metallodielectric photonic crystals (MDPCs) with multiple stopbands in the far-infrared transmission spectrum have been designed and fabricated using frequency selective surface (FSS) techniques at the micron-scale. These surfaces consist of self-similar fractal cross-dipole or fractal square patch metallic elements patterned on thin, flexible dielectric substrates using standard semiconductor microfabrication techniques. Optimization of design parameters, such as element spacing, through the application of a periodic method of moments (PMM) modeling code leads to experimental results with two transmission stopbands, each with greater than 10dB attenuation. These results are in excellent agreement with those predicted by the PMM model. The positions of the bands can be readily controlled by utilizing the modeling data to determine optimum element geometries.

3-) Dual-band infrared Single-layer metallidielectric Photonic Crystals
by R. P. Drupp, J. A. Bossard, Yong-Hong Ye, D. H. Werner, T.S. Mayer
Applied Physics Letters, Vol. 85, Number 10, September 6th, 2004

ABSTRACT: Metallodielectric photonic crystals (MDPCs) consisting of periodic arrays of self-similar two-stage fractal patch metallic elements patterned on thin dielectric substrates are shown to exhibit excellent mid- and far-infrared dual-band response in a single layer structure. This was achieved by optimizing the element size and interelement spacing of cross-dipole and square-patch fractal elements using full-wave periodic method of moments modeling techniques that calculate electromagnetic scattering from the MDPC surface and are able to account for material loss and loading effects. All structures fabricated based on these designs had two measured stopbands with greater than 10 dB attenuation positioned at wavelengths determined by element geometry and size as well as interelement spacing. This simple single layer fractal MDPC geometry will facilitate further scaling into the near-IR wavelength regime.

4-) The Design and Fabrication of Planar Multiband Metallodielectric Frequency Selective Surfaces for Infrared Applications
by Jeremy A. Bossard, Douglas H. Werner, Theresa S. Mayer, Jacob A. Smith, Yan U. Tang, Robert P. Drupp, and Ling Li
IEEE Transactions on Antennas and Propagation, Vol. 54, No. 4, pp. 1265 - 1276, April 2006.

ABSTRACT: In this paper, micron-scale frequency selective surfaces (FSS) are presented for the first time that exhibit multiple strong stopbands (>10dB) in the far-infrared (IR). Fractal and genetic algorithm (GA) synthesis techniques are employed in the design of single-layer, multiband IR FSS. These designs have been fabricated on thin, flexible polyimide substrates and characterized using Fourier transform infrared (FTIR) spectroscopy. Measurements show excellent agreement with predictions from a periodic method of moments (PMoM) analysis technique that takes into account metallic and dielectric losses. Additional design constraints were incorporated into the GA in order to guarantee that the synthesized FSS structures could be accurately fabricate

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