Controlling the Most Significant Grating Lobes in Two-Dimensional Beam-Steering Systems With Phase-Gradient Metasurfaces

Abstract

High-directivity antenna systems that provide 2D beam steering by rotating a pair of phase-gradient metasurfaces in the near field of a fixed-beam antenna, hereafter referred to as Near-Field Meta-Steering systems, are efficient, planar, simple, short, require less power to operate and do not require antenna tilting. However, when steering the beam, such systems generate undesirable dominant grating lobes, which substantially limit their applications. Optimizing a pair of these metasurfaces to minimize the grating lobes using standard methods is nearly impossible due to their large electrical size and thousands of small features leading to high computational costs. This paper addresses this challenge as follows. Firstly, it presents a method to efficiently reduce the strength of "offending" grating lobes by optimizing a supercell using Floquet analysis and multi-objective particle swarm optimization. Secondly, it investigates the effects of the transmission phase gradient of PGMs on radiation-pattern quality. It is shown that the number of dominant unwanted lobes in a 2D beam-steering antenna system and their levels can be reduced substantially by increasing the transmission phase gradient of the two PGMs. This knowledge is then extended to 2D beam-steering systems, where we demonstrate how to substantially reduce all grating lobes to a level below −20 dB for all beam directions, without applying any amplitude tapering to the aperture field. When steering the beam of two Meta-Steering systems with peak directivities of 30.5 dBi and 31.4 dBi, within a conical volume with an apex angle of 96 • , the variation in directivity is 2.4 dB and 3.2 dB, respectively. We also demonstrate that beam-steering systems with steeper gradient PGMs can steer the beam in a wider range of directions, require less mechanical rotation of metasurfaces to obtain a given scan range and their beam steering is faster. The gap between the two metasurfaces in a Near-field Meta-Steering system can be reduced to one-eighth of a wavelength with no significant effect on pattern quality.

Integration of Geometrically Different Elements to Design Thin Near-Field Metasurfaces

“…It is interesting to note that both the hybrid and reference metasurface increased the SLL of the beam. Unless extensive optimisations are done to reduce sidelobes and grating lobes, sidelobes of this level are common in beam-steering antenna systems based on metasurfaces [23]. We also investigated the polarization of the antenna with and without metasurface in the far-field region.…”

A System-Level Overview of Near-Field Meta-Steering

“…The operating principle of the PGMs is same as that of phased arrays. A typical PGM has unit cells having lateral dimensions smaller than λ0/2 [6,12]. In some all-metal type PGMs unit-cell elements slightly larger than λ0/2 are also used.…”

“…This gives direct control to change antenna beam direction between broadside direction and maximum elevation angle. Further details on beamscanning and metasurfaces rotation can be found in any of earlier publications [6,9,12]. One of the challenges associated with the phase wrapping and periodic nature of a PGM (as depicted in Fig.…”

“…A more accurate phase method was reported to predict direction of antenna beam using rotation angles of the PGMs [11]. A more recent investigation have reported optimized pair of PGMs to reduce undesirable grating lobes [12]. Considering the interest of the research community, this paper aims at introducing system level overview of the NFMS based antenna systems without focusing on detailed design procedures of individual components.…”

A Radial Line Slot-Array Antenna With Low Side Lobes and a Uniform-Phase, Tapered-Amplitude Aperture Field Distribution

“…RLSA antennas are considered one of the most attractive and versatile candidates as the base antenna for antenna beam steering systems based on Near-Field Meta-Steering [4]- [6] because of their promising features such as high gain, high efficiency, extremely low profile, and planar configuration [1], [7]- [19]. This paper presents an extremely high-gain radialline slot array (RLSA) antenna that is useful as the base antenna in such systems.…”