Dynamic Metasurface Reflectors Based on Coupled Resonators for Simultaneous Magnitude and Phase Control

Abstract

A novel metasurface reflector unit cell based on two coupled resonators is proposed and demonstrated for real-time reconfigurable beamforming in the X-band (8-12 GHz). The unit cell is composed of a splitring resonator (SRR) with tunable capacitance and a dipole-ring resonator (DRR) with tunable resistance, whose collective variations allow for control over the complex reflectance at a desired frequency. To gain physical insight into its working mechanism, the proposed unit cell is modeled as a coupled Lorentz oscillator using the surface susceptibility description of the unit cell. Thereafter, a metasurface reflector based on the proposed unit cell is demonstrated in full-wave simulations to achieve various beamforming examples, such as beam-steering, side-lobe level control, beam-steering with amplitude control, and multibeam patterns, from a single normally-incident plane wave excitation. Three metasurface reflectors are fabricated to experimentally demonstrate the proposed concept; the first is based on an SRR with a varactor diode, the second is based on a DRR with a PIN diode, and the third is based on the proposed coupled SRR-DRR configuration with both varactor and PIN diodes, for simultaneous magnitude and phase control. The metasurface reflector based on the coupled resonator unit cell is experimentally demonstrated to achieve versatile beam transformations including beam-steering with amplitude control and multi-beam patterns.INDEX TERMS metasurface reflectors, beamforming, side-lobe level control, beam-steering, multibeam patterns, complex reflectance, reconfigurable intelligent surfaces, coupled resonators, smart radio environments.

Waveguide-Floquet Mapping Using Surface Susceptibilities for Passive and Active Metasurface Unit Cell Characterization

“…An excellent match between the two confirms that the extraction is successful across the entire frequency range. This is further validated by reconstructing the reflection response (both magnitude and phase) at various incidence angles following (10) and comparing it with the fullwave response obtained from Ansys HFSS. For comparisons, the reflection response of the two waveguides has also been superimposed with the reconstructed reflection for each angle, and it is clear that the intrinsic waveguide response is very different, and thus inaccurate, from the desired unit cell response in general.…”

“…Next, consider another class of metasurface structures consisting of purely reflective unit cells, which are commonly used for making metasurface reflectors [10], [42]. Such unit cells consist of a sub-wavelength resonator on one side and a solid ground plane (modelled as PEC here) on the other.…”

“…In contrast to passive metasurfaces, these structures typically consist of tunable lumped circuit elements (e.g. capacitors and resistors) [6]- [10] or advanced dynamically tunable exotic materials, such as graphene, ferroelectrics or conductive oxides, to name a few [11]. Here, while the physical geometry of the resonators is fixed across the array, the reflection/transmission characteristics (i.e.…”

“…Therefore, the development and prototyping of a complete final metasurface structure is both complex and expensive. Furthermore, practical uncertainties in lumped circuits and material parameters, typically lead to large phase/frequency shifts (in reflection and/or transmission) and losses, which makes a direct prototyping of a complete array a risky design approach [9], [10].…”