This paper presents the concept and design of a reflectarray nanoantenna at optical frequencies whose elements are nano-sized concentric spherical particles with the core made of ordinary dielectrics and the shell made of a plasmonic material. Modeling approaches based on finite difference time domain (FDTD) numerical method and dipole-modes scattering theory are used to characterize and tune the reflectarray design. A 6x6 elements reflectarray nanoantenna operating at wavelength 357.1nm with narrow beamwidth is presented, and its scanned radiation characteristics for 15 degrees and 30 degrees are demonstrated.

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The goal of this letter is to present the behavior of mu-negative (MNG) metamaterial-based electrically small antennas. The Green's function analysis is applied to characterize the performance of a hemispherical negative permeability (MNG) resonator excited by a slot aperture. The method of moment (MoM) is used to obtain the current distribution over the source excitation. It is illustrated how a resonator composed of negative permeability medium can successfully establish a small antenna element. For small-size structure (ka < 0:5), the approximated-form Green's function demonstrates the relation between the resonant frequencies and the material parameters. The obtained results are integrated into the design of a MNG slab radiator. The radiation performance of a slab resonator is detailed using a finite difference time domain (FDTD) full wave analysis. The obtained observations may provide road maps for the future design of metamaterial-based subwavelength antennas.

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In this paper, we theoretically characterize the performance of array of plasmonic core-shell nano-radiators located over layered substrates. Engineered substrates are investigated to manipulate the radiation performance of nanoantennas. A rigorous analytical approach for the problem in hand is developed by applying Green's function analysis of dipoles located above layered materials. It is illustrated that around the electric scattering resonances of the subwavelength spherical particles, each particle can be viewed as an induced electric dipole which is related to the total electric field upon that particle by a polarizability factor. Utilizing this, we can effectively study the physical performance of such structures. The accuracy of our theoretical model is validated through using a full-wave finite difference time domain (FDTD) numerical technique. It is established that by novel arraying of nano-particl and tailoring their multilayer substrates, one can successfully engineer the radiation patterns and beam angles. Several optical nanoantennas designed on layered substrates are explored. Using the FDTD the effect of finite size substrate is also explored.