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Compact Reconfigurable Intelligent Surface with Phase-Gradient Coded Beam Steering and Controlled Substrate Loss

Mahendra Kheti, Debapratim Ghosh, Soumya P. Dash

Abstract

This paper presents a 1-bit reconfigurable intelligent surface (RIS) fabricated using a three-layer structure. It employs a manual layer stackup incorporating an optimal air gap to reduce the effective dielectric losses while using a low-cost FR4 substrate. The new design of the unit cells of the proposed RIS is outlined, with each unit cell featuring a PIN-diode-based, compact, simplified biasing network that simplifies the control circuit while maintaining distinct $\boldsymbol{0^\circ/180^\circ \pm 20^\circ}$ phase states between ON/OFF conditions. The designed RIS is in the form of a $\boldsymbol{10\times10}$ array with a compact size of $\boldsymbol{2.9λ_g \times 2.9λ_g}$. Additionally, a phase-gradient coding scheme is presented and utilized that achieves measured beam steering up to $\boldsymbol{\pm30^\circ}$ in both anechoic and noisy environments. Controlled and driven by an Arduino-cum-digital interface, the proposed RIS exhibits measured reflected wave gain enhancement of about 9\,dB over an incident wave angular range of $\boldsymbol{\pm 30^\circ}$. Furthermore, the design is also experimentally validated by transmitting quadrature phase-shift keying-modulated symbols via the RIS-assisted wireless channel. The proposed RIS works for the range 3.38--3.67\,GHz (8.3\%), and is suitable for deployment for the 5G n78 \mbox{band (3.5\,GHz).}

Compact Reconfigurable Intelligent Surface with Phase-Gradient Coded Beam Steering and Controlled Substrate Loss

Abstract

This paper presents a 1-bit reconfigurable intelligent surface (RIS) fabricated using a three-layer structure. It employs a manual layer stackup incorporating an optimal air gap to reduce the effective dielectric losses while using a low-cost FR4 substrate. The new design of the unit cells of the proposed RIS is outlined, with each unit cell featuring a PIN-diode-based, compact, simplified biasing network that simplifies the control circuit while maintaining distinct phase states between ON/OFF conditions. The designed RIS is in the form of a array with a compact size of . Additionally, a phase-gradient coding scheme is presented and utilized that achieves measured beam steering up to in both anechoic and noisy environments. Controlled and driven by an Arduino-cum-digital interface, the proposed RIS exhibits measured reflected wave gain enhancement of about 9\,dB over an incident wave angular range of . Furthermore, the design is also experimentally validated by transmitting quadrature phase-shift keying-modulated symbols via the RIS-assisted wireless channel. The proposed RIS works for the range 3.38--3.67\,GHz (8.3\%), and is suitable for deployment for the 5G n78 \mbox{band (3.5\,GHz).}

Paper Structure

This paper contains 9 sections, 23 equations, 16 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Proposed Unit Cell Structure and Modeling
  3. Geometry and Layered Structure
  4. Phase Sensitivity and Via Placement Under Floquet Port Excitation
  5. Theoretical Modeling of Planar Reflection-Mode RIS
  6. Experimental Setup and Measurement Procedure
  7. Experimental Verification and Results
  8. Effect of the RIS on QPSK Constellation
  9. Conclusion

Figures (16)

  • Figure 1: Cross-sectional view of the proposed RIS unit cell illustrating various layers.
  • Figure 2: (a) Radiating layer (b) ground layer and (c) bias layer of the RIS unit cell. Equivalent circuits of the PIN diode (Skyworks SMP1345-079LF) in (d) ON state and (e) OFF state.
  • Figure 3: Equivalent circuit model of the proposed biasing layer, including the PIN diode and associated passive components.
  • Figure 4: Simulated reflection coefficient of the RIS unit cell under different operating conditions.
  • Figure 5: Simulated reflection coefficient phase response of the RIS unit cell under different operating conditions.
  • ...and 11 more figures