Abstract
As reconfigurable intelligent surface (RIS) is expected to be implemented with a large aperture in terms of wavelengths, using a RIS to perform near-field rather than conventional far-field communications might gain some benefits. The electric fields in the near-field region from the near-field focusing and conventional far-field RISs are simulated and compared to assess and validate the benefits. Two metrics of benefit distance and near-field gain are defined to characterize the electric fields in the near-field region. The cumulative distribution function (CDF) related to the near-field gain is calculated to describe the benefits in the area of interest where the total scan patterns from the near-field focusing and conventional far-field RISs are plotted. For demonstration, the benefit distance, near-field gain, and CDFs are presented and calculated for near-field focusing RISs with assigned focal distances of 80 and 300 mm. It is concluded that the benefit distance is a critical factor affecting the CDF directly. The effects of the size of a RIS and phase quantization of elements on the benefit distance, near-field gain, and CDF are also discussed. Moreover, the maximum focal distance of a near-field focusing RIS with a certain size is derived and specified. Finally, the electric fields of three prototypes (e.g., conventional far-field RIS, near-field focusing RISs with assigned focal distances of 500 and 1500 mm) at 26 GHz are measured and compared, where the benefit distances and near-field gains are experimentally observed.
Original language | English |
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Journal | I E E E Transactions on Antennas and Propagation |
Volume | 70 |
Issue number | 10 |
Pages (from-to) | 8718-8728 |
Number of pages | 11 |
ISSN | 0018-926X |
DOIs | |
Publication status | Published - Nov 2022 |
Keywords
- Cumulative distribution function (CDF)
- electric fields
- near-field focusing
- reconfigurable intelligent surfaces (RISs)