  Reconfigurable intelligent surface (RIS) can improve the communications
between a source and a destination. Recently, continuous aperture RIS is proved
to have better communication performance than discrete aperture RIS and has
received much attention. However, the conventional continuous aperture RIS is
designed to convert the incoming planar waves into the outgoing planar waves,
which is not the optimal reflecting scheme when the receiver is not a planar
array and is located in the near field of the RIS. In this paper, we consider
two types of receivers in the radiating near field of the RIS: (1) when the
receiver is equipped with a uniform linear array (ULA), we design RIS
coefficient to convert planar waves into cylindrical waves; (2) when the
receiver is equipped with a single antenna, we design RIS coefficient to
convert planar waves into spherical waves. We then propose the maximum
likelihood (ML) method and the focal scanning (FS) method to sense the location
of the receiver based on the analytic expression of the reflection coefficient,
and derive the corresponding position error bound (PEB). Simulation results
demonstrate that the proposed scheme can reduce energy leakage and thus enlarge
the channel capacity compared to the conventional scheme. Moreover, the
location of the receiver could be accurately sensed by the ML method with large
computation complexity or be roughly sensed by the FS method with small
computation complexity.
