Reconfigurable Meta-Coupler Employing Hybrid Metal-Graphene Metasurfaces

Graphene-based terahertz reconfigurable printed ridge gap waveguide structure

Graphene-based microwave devices have enabled reconfigurability, thus paving the way to the realization of flexible wireless terahertz systems with featured performances. Despite great progress in the development of graphene-based terahertz devices in the literature, high insertion loss and wide tunable range are still significant challenges at such high frequencies. In this work, we introduce the use of graphene to implement a reconfigurable printed ridge gap waveguide (RPRGW) structure over the terahertz frequency range for the first time. This guiding structure is suitable for both millimeter and terahertz wave applications due to its supporting quasi-TEM mode, which exhibits low dispersion compared to other traditional guiding structures. The presented solution is featured with low loss as the signal propagates in a lossless air gap, which is separated from the lossy graphene elements responsible for the reconfigurable behavior. In addition, this guiding structure is deployed to implement a tunable RPPGW power divider as an application example for the proposed structure.

Dynamic and complete terahertz wavefront manipulation via an anisotropic coding metasurface

A reconfigurable anisotropic coding metasurface composed of a graphene layer and anisotropic Jerusalem-cross metallic layer is proposed for dynamic and complete multi-channel terahertz wavefront manipulation. By controlling the Fermi energy of graphene, continuous amplitude modulation is realized for the coding elements with certain phase responses. By arranging anisotropic phase coding elements with a specific coding sequence and changing the Fermi energy of graphene, the proposed metasurface can dynamically control multi-channel reflection beams with designed power distribution and simultaneously manipulate the scattering pattern from diffusion to mirror scattering under x- and y-polarized incidence, respectively. Compared with the dynamic phase modulation metasurface, such a tunable metasurface uses three degrees of freedom, including the polarization, phase, and amplitude responses to fully control the reflected wavefronts, which may have promising applications in tunable terahertz multi-functional holograms and multi-channel information communication.

Inverse design of compact power divider with arbitrary outputs for 5G applications

Since the recent on-demand applications need more sophisticated circuits and subsystems, components with configurable capabilities attract attention more than before in commercial systems, specifically the fifth generation (5G). Power dividers play a crucial role in 5G phased array systems, and their role becomes more significant if the output powers ratio is adjustable. Here, we suggest a design methodology by which planar power splitters with arbitrary output power levels can be designed in light of very simple perturbations, i.e., vias. Through our design procedure, we find an optimized pattern for hybrid vias-some of them are made of PEC, and others are dielectric, e.g., air, high-permittivity materials. Thanks to deep neural networks, we demonstrate that this technique can be employed to design power splitters whose output ports have different amplitudes. In light of the proposed method, we fabricated and measured a 4-way power divider realizing Chebyshev coefficients for sidelobe reduction of a 4-element array at 28 GHz as a proof-of-concept. We believe that this methodology in which hybrid perturbation is the key spot paves a way to implement complex functions in various platforms and other structures, e.g., SIWs, ridge waveguides, rather than the one we investigated (planar/microstrip).

Ultra-low-loss tunable piezoelectric-actuated metasurfaces achieving 360° or 180° dynamic phase shift at millimeter-waves

Phase shifting metasurfaces typically consist of an ordered metallic geometry that is patterned onto a dielectric substrate and incorporate active devices or materials that enable dynamic tuning. Existing methods at mm-wave and submillimeter bands typically suffer from high losses, which are predominantly produced by the inherent limitations of the tuning elements or materials. This report presents a new, ultra-low-loss and phase-tunable, reflection type metasurface design, which outperforms previously reported technologies in terms of phase shifting and loss. The proposed technique utilizes a variable air cavity, formed between a periodic array and a ground plane, which is controlled by means of a piezoelectric actuator. Two metasurface designs are presented and experimentally tested. Firstly, a square patch element metasurface that is capable of achieving a continuous 180° phase shift across a wide bandwidth, between 35 and 65 GHz. Also presented is a double-cross element metasurface that provides full 360° phase control between 57 and 62 GHz. The variable air cavity is controlled by means of a piezoelectric actuator that supports and varies the height of a ground plane, providing highly accurate, millisecond, displacement. Unlike conventional tuning methods, the tuning mechanism, in this case the moving ground plane, introduces no additional sources of loss and enables an average loss performance of 1 dB. Full-wave simulations are presented and experimentally validated with measurements of both metasurface prototypes. The proposed approach is scalable from microwave up to THz frequencies, due to the electro-mechanical and low loss nature of the tuning.