Simultaneous High-Efficiency Anomalous Reflection and Angle of Arrival Sensing in Reconfigurable Intelligent Surfaces

Abstract

In this work, we introduce reconfigurable intelligent surfaces designed to simultaneously perform reflection of single or multiple incident waves toward the receiver or receivers and sensing the angles of arrival. We achieve anomalous reflection with strongly suppressed parasitic scattering through an in-situ optimization of either the currents flowing on array elements or the far field in the receiver direction. The suppression of parasitic scattering allows us to accurately and without additional measurements or computations detect the angles of arrival of the illuminations through the spatial Fourier transform of the optimized current distribution through the controllable reactive loads. Therefore, unlike other recently proposed methods, our scheme of integrated sensing and communication does not require any pre-computed data sets and works for an arbitrary number of simultaneous illuminations. As a proof of principle, we design and analyze with full-wave simulations several reconfigurable intelligent surfaces consisting of an array of loaded wires above a ground plane.

Figures (8)

• Figure 1: An illustration of the principle of the proposed solution. (a) Before optimization, a random distribution of load impedances leads to a complicated reflected field. The bottom plot qualitatively illustrates the Fourier transform of surface-averaged electric current passing through the loads along a certain direction (in the particular examples below that will be in the incidence plane, ${\bf k}_{||}=k_y{\hat{y}}$). (b) By optimizing the load impedances and subsequently the current distribution in the controllable array elements, the RIS anomalously reflects a single plane wave to the receiver direction. At the bottom, the spatial Fourier transform of the optimized current is shown. Because the optimal anomalous reflection implies elimination of the specular reflection from the ground plane, the second peak position reveals the direction of arrival of the incident wave.
• Figure 2: An illustration of an array of loaded wires above a PEC ground plane. The structure is illuminated with a TE polarized plane wave at an unknown angle $\theta_{\rm i}$. The wires are oriented horizontally along the $y$-axis at the distance $h$ from the ground plane and separated by $d$ from each other. The inset shows the $xy$-plane view of a single wire loaded by a tunable distributed impedance. The final goal is to create a reflected beam toward the receiver direction by optimizing the tunable loads and determine the incident angle $\theta_{\rm i}$.
• Figure 3: Continuous spatial spectrum of the optimized solution for wire currents when the distance between the wires is set to $d=\lambda/10$. The other key parameters for this solution are: $h=\lambda/6, N=111, r_0=\lambda/100$, and the whole size of the array is $N\times d= 11\lambda$. The frequency is set to $f=10$ GHz, and the receiver is located at $\theta_ {\rm r}= 70^\circ$.
• Figure 4: a) The optimized total reflected (sum of the field generated by wires and by the ground plane) field distribution based on the objective function Eq. \ref{['Eq:first_obj']}, when there are 111 wires with $\lambda/10$ distance between them. (b) The corresponding far-field scattering pattern. In this calculation, we assume a finite-sized ground plane, of the same size as the array of loaded wires.
• Figure 5: Spatial spectrum of the optimized solution (based on Eq. \ref{['Eq:far_obj']}) for wire currents when the distance between the wires is set to $d=\lambda/10$. The other key parameters for this solution are: $h=\lambda/6, N=111, r_0=\lambda/100$, and the whole size of the array is $N\times d= 11\lambda$. The blue line represents all current harmonics, while the green and red vertical lines correspond to the harmonics associated with the reflected and incident wave directions, respectively. Two black lines delineate the boundaries of the propagation range, where $k_{||}=k_0$.