Abstract
Broadening the bandwidth, increasing the modulation level, and increasing spatial multiplexing order are potential pillars to improve the performance of wireless communication systems. Accordingly, this research proposes broadening the transmission bandwidth and employing spatial multiplexing to increase the capacity of future wireless networks. Resorting to high-spectrum resources has been suggested as an inevitable act to handle the flying demand on the internet to secure the needed bandwidth. Moreover, waves-carrying orbital angular momentum (OAM) have emerged as an additional degree of freedom in electromagnetic (EM) systems to promote higher data rates by exchanging several data streams over the same bandwidth. As obtaining practical solutions for future networks is of the main motives of this work, other technical aspects are carefully considered, such as cost, volume, weight, and ease of fabrication. Thus, low-profile and high-gain metasurfaces are employed to produce OAM waves with different modes, enable steerable OAM waves, and deliver OAM multiplexing. Reflectarray antennas and reflecting metasurfaces are used to generate helical waves by novel topologies at different frequencies. Various techniques are proposed to broaden the narrow bandwidth of periodic structures at the 5G millimetre wave (mmWave) and terahertz (THz) bands.
The chief achievements of this research are reducing the feeder blockage effect of reflectarrays for the generated low-divergence high-gain OAM beams at 5G-mmWave frequencies, introducing the world's first technique to realize OAM multiplexing via a passive THz reflectarray illuminated by a single feeding source, and enabling the non-Line-of-Sight (NLoS) component of the high gain THz OAM beams and improving spectral efficiency through reflective metasurfaces. To this end, a MATLAB GUI tool is developed to acquire the required phase distribution of seamless phase variation. Promising results are obtained from the simulated and fabricated prototypes of different features and frequency ranges.