Joint Beam and Polarization Forming of Intelligent Reflecting Surfaces for Wireless Communications

In this paper, we propose a novel intelligent reflecting surface (IRS) structure, which is capable of jointly forming desirable beam and polarization of a reflected wave with the aid of massive reflecting elements. More specifically, the proposed IRS is composed of unit cells, each having multiple variable capacitors. Active tuning of capacitances of the variable capacitors in each unit cell provides the full coverage of 360° in the reflection phase. Furthermore, polarization is switched from an incident wave to the reflected wave through the excitation of two orthogonal modes, enabling arbitrary phase distribution over the IRS for the desired polarization. As a result, the proposed IRS allows the increase of the signal-to-noise ratio (SNR) at the receiver in a communication scenario, by adjusting the reflection phase shift of each IRS element. Moreover, the reflection phase shifts of each IRS element are optimized with the aid of the Newton method, such that the received signal power of a receiver is maximized. In our simulations, it is demonstrated that our proposed IRS successfully maximizes the SNR at the receiver, both in the single-user and the broadcast multi-user scenarios, where multi-user interference is absent.