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Meta 2010 & FEM 2010 – Rome, 13-15 December 2010 Experimental investigations on woodpile EBG metamaterials Luca Di Palma (1) , Fabrizio Frezza (2) , Lara Pajewski (1) , Emanuele Piuzzi (2) , Cristina Ponti (1) , Giorgia Rossi (1) , and Giuseppe Schettini (1) (1) Roma Tre University, Department of Applied Electronics Rome, Italy – E-mail: g.schettini@uniroma3.it (2) Sapienza University, Department of Information Engineering, Electronics, and Telecommunications Rome, Italy – E-mail: fabrizio.frezza@uniroma1.it Electromagnetic Band.Gap (EBG) materials are a class of artificial materials made by a periodic arrangement of dielectric and/or metallic unit cells, which allow to control the propagation of electromagnetic waves along certain directions, depending on the periodicity [1]. They can be employed to design a novel class of planar antennas, with properties of enhanced directivity [2]-[5]. In this work, a three-dimensional EBG with woodpile unit cell is presented, that has been implemented into two alumina prototypes. Experimental measurements have given a full characterization of the frequency selectivity through the structure, especially when employed as a cavity resonator, with two identical mirrors separated by an air-gap. For this particular layout, the effect of the field polarization, and of the gap length, on the frequency response, has been deeply investigated. The main result is the existence of transmission peaks when the air-gap is a multiple of the wavelength, which, as far as symmetric cavities are concerned, may be applied to the design of resonator antennas. Starting from a microstrip patch, a new compound radiator has been built, placing the ground plane of the basic radiator in the symmetry plane of the EBG resonator, and removing its lower part. Many antenna layouts can be implemented, according to the woodpile orientation, and the distance between the ground plane and the woodpile superstrate. Compared to the basic radiator, the woodpile-covered antenna has narrow beam-width, and reduced side-lobe level, and a gain enhancement up to 10 dB has been measured on several antenna layouts. References [1] J. D. Joannopoulos et al., Photonic Crystals: Molding the Flow of Light, Princeton University Press, Princeton NJ 2008. [2] F. Yang and Y. Rahmat-Samii, Electromagnetic Band Gap Structures in Antenna Engineering, Cambridge University Press, New York 2009. [3] Y. J. Lee, J. Jeo, R. Mittra, and T. S. Bird, “Application of Electromagnetic Bandgap (EBG) superstrates with controllable defects for a class of patch antennas as spatial angular filters,” IEEE Trans. Ant. Propag., 53, 224-235, 2005. [4] A. R. Weily, L. Horvath, K. P. Esselle, B. C. Sanders, and T. S. Bird, “A planar resonator antenna based on a woodpile EBG material,” IEEE Trans. Ant. Propag. 53, 216-223, 2005. [5] F. Frezza, L. Pajewski, E. Piuzzi, C. Ponti, and G. Schettini, Analysis and experimental characterization of an alumina woodpile-covered planar antenna,” Proc. 40th European Microwave Conference 2009, 200-203, Paris, France, Sept. 28-30 2010. 54
Meta 2010 & FEM 2010 – Rome, 13-15 December 2010 Analytical Model of Connected Bi-Omega Structures for Enhanced Microwave Transmission Filiberto Bilotti, Luca Di Palma, and Lucio Vegni “Roma Tre” University, Department of Applied Electronics Rome, Italy – E-mail: bilotti@uniroma3.it In this contribution, we present a new analytical model of two connected biomega particles (Figure 1a). Exploiting the analytical models of chiral and planar omega particles [1-2] and the equivalent circuit of the bi-helix particle [3], we have developed a new analytical model for the isolated bi-omega particle (i.e. a single omega particle backed by its reversed replica). Assuming the particle electrically small, the proposed analytical model is given in terms of a proper lumped element equivalent circuit. Then, we have extended the model to the case of two connected bi-omega particles, by considering the relevant coupling terms. Since this structure is symmetric, it does support two fundamental modes, characterized by an even and an odd electric field distribution, respectively. The analytical model, in fact, predicts two different resonant frequencies related to the two modes of operation. Such a result is confirmed also by proper full-wave numerical simulations (Figure 1b). The proposed analytical model has been successfully used to design compact devices to obtain extraordinary transmission through sub-wavelength apertures in metallic waveguides. This result opens the door to the design of a new class of microwave components (filters, impedance matching devices, mode converters, cavity resonators, miniaturized probes and radiating systems, etc.), some of which will be shown at the conference. 55 Magnetic field amplitude [A/m] 25 20 15 10 5 “even” mode “odd” mode 0 0 1 2 3 4 5 Frequency [GHz] d) b) Figure 1 – a) Sketch of two connected bi-omega particles and b) its typical resonant behavior. References [1] S.A. Tretyakov, et al. “Analytical Antenna Model for Chiral Scatterers: Comparison with Numerical and Experimental Data,” IEEE Trans. Antennas Propagat., 44, 1006-1014, 1996. [2] C.R. Simovski, S.A. Tretyakov, A.A. Sochava, “Antenna Model for Conductive Omega Particles,” J. Elettromag. Waves Applicat., 11, 1509-1530, 1997. [3] A.N. Lagarkova, et al. “Resonance Properties of Bi-helix Media at Microwaves,” Electromagnetics, 17, 213-237, 1997.
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Abstracts - Dipartimento di Elettronica Applicata

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