Executive Summary : | The metasurface is the primary hardware of RIS, which allows for manipulation of electromagnetic wave properties at the sub-wavelength scale. Space-time gradient metasurfaces are achieved by applying time modulation to the surface impedance's electrical properties, breaking the time-reversal symmetry and performing space-time modulation of EM waves. Programmable digital coding schemes are used to streamline metasurface design optimization and control their real-time reconfigurability. A dynamic reflect array with omnidirectional antennas with configurable termination is used to implement a RIS in its basic form. Passive RIS designs have advantages like low noise and SNR proportional to N2, but these gain capacities are rarely seen in everyday communication due to the "multiplicative fading" effect introduced by RISs. This phenomenon makes it difficult for passive RISs to produce meaningful capacity improvements in many wireless situations. To circumvent this physical restriction, active RIS architecture for wireless communication systems is needed. Active RISs actively reflect signals with amplification, achieved by incorporating reflection-type amplifiers or current inverting amplifiers into the reflecting elements. Active RIS has the potential to mitigate the multiplicative fading effect by compensating for the substantial route loss of reflected links at the expense of additional power consumption. This project will develop an active RIS prototype, loaded to amplifier circuitry to demonstrate the RIS advantages, which are mitigated due to the multiplicative fading effect. Later, this active RIS will focus on active beam forming and information encoding applications. |