الفهرس 
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Abstract
Modern wireless communication systems require antennas with high gain and beam-steering capability to provide user mobility or beam switching for reconfigurable backhauling. The high antenna gain requires a large antenna aperture that scales proportionally to the square of the wavelength. At the same time, the high gain antenna leads to a very narrow beam, which requires perfect adjustment of the fixed antennas and special beam-steering and beam-tracking algorithms for mobile applications.
MSs are sub-wavelength scale, two-dimensional (2D) periodic structures being extensively studied due to their distinctive capability to manipulate electromagnetic waves in areas of antennas, absorbers, surface waveguides, cloaking, modulators, polarizers, lenses, and imaging at the microwave and optical frequencies. In this work, we studied the advantages of loading antennas with MSs expressly in fields of gain enhancement and multi-band operations, which overcomes some limitations of conventional approaches.
A compact MS-based antenna with dual-band operation for future 5G applications is proposed based on MS structures. The MS-based antenna is comprised of a layer of MSs on the top of a single-band microstrip patch antenna. The dual-band operation is achieved by adding the MS layer at a height of 1 mm (0.089λ₀). The patch antenna is designed on a 21 mm × 20 mm × 0.508 mm Rogers 5880 substrate. The MS is comprised of two metallic layers designed on the top and bottom of a 1.575 mm substrate. To verify the operation of the antenna, a prototype is manufactured and evaluated. The configuration achieves dual-band features with impedance matching better than -20 dB. Also, the lower frequency band fulfills a bandwidth of more than 1 GHz across the frequency range from 25.7 GHz to 26.75 GHz with a center frequency of 26.4 GHz. On the other hand, a bandwidth of 800 MHz over the frequency range of 27.2 GHz to 28 GHz is obtained at the higher frequency band with a resonant frequency of 27.6 GHz. Furthermore, a gain of 10 dBi and 9.6 dBi is obtained at a frequency of 26.4 GHz and 27.6 GHz, respectively. Also, the high radiation efficiency of 96.4% and 96.2% is obtained at the center frequency of the two former frequency bands, respectively.
Also, a Mu-near-zero MS (MNZ-MS) layer is embedded within a microstrip patch antenna to constitute a high gain antenna that can be used for future 5G applications. To improve the antenna gain, a layer of MNZ-MS unit cells is placed above the antenna substrate with 0.48λ0 air space between the two layers, where λ0 is the free space wavelength at the resonance frequency (26.3 GHz). The MNZ-MS layer consists of 4 double-sided split square resonators, printed on a substrate of thickness 1.575 mm. The overall thickness of the suggested antenna is 0.66λ0. To verify the operation of the antenna, a prototype is manufactured and evaluated. The results fulfill a better than -10 dB reflection coefficient across the frequency spectrum of 26 GHz–28 GHz. A gain enhancement better than 5 dBi is obtained compared to the gain of the reference patch at the resonance frequency of 26.3 GHz. Also, a high radiation efficiency of 93.9% is obtained.
Furthermore, a high-gain dual-band FP antenna is composed of two different layers of MS and a single band source patch antenna for future 5G applications is designed. The MS layers are positioned above the source patch antenna with an air space between every two layers. The lower MS layer has a characteristic of high/low-Z (HLZ-MS) behavior that can be used to construct the first FP cavity with the ground of the source patch to achieve dual-band functionality. Meanwhile, the higher MS layer serves as the partially-reflective-surface (PRS-MS) of the second FP cavity with the HLZ-MS layer which can achieve the desired gain enhancement at the two frequency bands. The antenna fulfills the dual-band operation with impedance matching better than -17 dB at a center frequency of 26.81 GHz and 28.83 GHz with a bandwidth of 660 MHz and 650 MHz for the two bands, respectively. The proposed antenna has an overall thickness of 1.04λ0, where λ0 is the free space wavelength of the lower resonant frequency. Also, a high gain of 12.2 dBi and 12.3 dBi is obtained at the lower and higher resonant frequencies, respectively, with gain enhancement better than 4 dBi in comparison with the gain of the reference patch antenna at its resonance frequency.