QPSO-optimized gain-enhanced Koch fractal antenna using NZIM superstrate for satellite and air-borne application
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QPSO-optimized gain-enhanced Koch fractal antenna using NZIM superstrate for satellite and air-borne application Mohammed Ismail Mohammeda
, Gebermichael Youhannes
Ethiopian Institute of Technology, Mekelle University, Mekelle, Ethiopia Received: 9 April 2020 / Accepted: 27 June 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The proposed work presents Koch fractal antenna, with feed optimization using quantum particle swarm optimization (QPSO), and near-zero-index material (NZIM) superstrate to enhance gain. The gain enhancement achieved here uses the unique property of NZIM to collimate divergent broadside radiations emanating from planar array patch antenna. The metamaterial unit cell, called the electric field-coupled resonator designed as NZIM, is configured into a 2 × 2-array structure and used as a double-layer superstrate. The distances from the patch to the superstrate and between the adjacent superstrate layers are optimized for maximum gain using QPSO. The Koch fractal used in conjunction with the proposed NZIM results in dual-band and wideband operation with a significant gain enhancement achieved in the first band and moderate enhancement in the second band, with a large inter-band separation that minimizes co-channel interference.
1 Introduction The emergence of metamaterial has provided an opportunity for researchers to develop novel structures by designing subwavelength elements working within a frequency range and exhibiting unconventional properties not seen in natural materials [1, 2]. Three different categories of metamaterial that have been used extensively are: metamaterial with permittivity near to zero (ENZ), metamaterial with both permittivity and permeability near to zero (ZIM), and metamaterial with refractive index near to xero (NZIM). The ENZ has found use in diverse applications such as transmission re-enhancement in a particular direction [3–5], wavefront shaping and cloaking [6, 7] and controlled spontaneous emission [8, 9]. The ZIM finds an extensive use in energy tunneling and beam focusing effect to enhance gain/directivity[10]. On the other hand, near-zero-index metamaterial material (NZIM) has the property such that if the interface from which the waves exit is flat, the refracted waves gets collimated in a direction perpendicular to the interface as shown in Fig. 1b. This property of the NZIM exploited in a number of interesting applications such as antenna beam focusing for gain and directivity enhancement. Gain and directivity enhancement of an antenna using metamaterial as a superstrate is handled by researchers differently. Ju et al. [11] proposed a high-gain microstrip antenna
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Eur. Phys. J. Plus
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Fig. 1 Electric field-coupled resonator metamaterial under arbitrary incidence
covered with ZIM as a superstrate. Zhou et al. [12] studied the performance of high-directivity microstrip pa
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