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Abstract-This paper presents the study of a circular slot antenna for ultrawide-band (UWB) applications. Antenna is fed by a circular open ended microstrip line. The frequency band considered is from 4 to 14 GHz, which has approved as a commercial UWB band. The proposed antenna has a return loss less than 10 dB, phased linear, and gain flatness over the above a frequency band.

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.