  As an emerging wireless communication technology, reconfigurable intelligent
surface (RIS) has become a basic choice for providing signal coverage services
in scenarios with dense obstacles or long tunnels through multi-hop
configurations. Conventional works of literature mainly focus on alternating
optimization or single-beam calculation in RIS phase configuration, which is
limited in considering energy efficiency, and often suffers from inaccurate
channel state information (CSI), poor convergence, and high computational
complexity. This paper addresses the design and optimization challenges for
successive RIS-assisted multi-hop systems. Specifically, we establish a general
model for multi-hop communication based on the relationship between the input
and output electric fields within each RIS. Meanwhile, we derive the half-power
beamwidth of the RIS-reflected beams, considering the beam direction.
Leveraging these models and derivations, we propose deployment optimization and
beam optimization strategies for multi-hop systems, which feature high aperture
efficiency and significant gains in signal power. Simulation and prototype
experiment results validate the effectiveness and superiority of the proposed
systems and methods.
