Single-Beam 1 Bit Reflective Metasurface Using Prephased Unit Cells for Normally Incident Plane Waves

A single-beam prephased 1 bit reflective metasurface is proposed to achieve single-beam patterns under normally incident plane waves. Theoretical analysis and numerical simulations are presented to show that, under normally incident waves, single-beam patterns can be achieved by introducing a fixed prephase distribution with two values in the 1 bit metasurface. Compared with conventional 1 bit reflective metasurfaces, the proposed scheme alleviates the inherent limitation of single-beam patterns on 1 bit reflective metasurfaces under normally incident plane waves. To verify the proposed scheme, a 1 bit unit cell is designed with a 180°±25° phase difference between the two states for frequencies ranging from 34.3 to 49.9 GHz, and a layer-stacking method is proposed to achieve two prephases with a 90° phase difference. As an example, three 1 bit reflective metasurfaces comprising 20 × 20 unit cells with single beams pointing separately at 0°, 15°, and 30° are designed and measured over frequencies of 37.0 to 41.0 GHz; the measured sidelobe levels are less than -7.8 dB. Simulated and measured results show that the proposed prephased 1 bit metasurface can achieve single-beam patterns under normally incident plane waves.

I. Introduction

The manipulation of electromagnetic (EM) waves has recently attracted substantial attention with the development of metasurfaces as well as the increasing requirements on wireless communications [1]–[4]. One of the challenges facing the millimeter wave (mmWave) is penetration loss, which restricts the development and applications of mmWave indoor communication. Nevertheless, penetration loss can be alleviated if a surface can guide incoming plane waves from one room to another rather than let the waves penetrate through a thick wall. For example, mmWave penetration loss can be avoided or diminished if a series of reflective metasurfaces, which can manipulate incoming plane waves toward an arbitrary direction, are used to guide those waves without penetrating the concrete walls [5]. Therefore, reflective metasurfaces, which can guide incident plane waves to the desired direction, have excellent potential for indoor mmWave wireless communications.