Yao-Ping Zhang

A Reconfigurable Graphene Reflectarray for Generation of Vortex THz Waves

A reconfigurable graphene reflectarray is proposed for the generation of vortex radio waves at THz. First, a simple sectored circular reflective surface model with a plane wave at normal incidence is constructed to illustrate how vortex radio waves can be generated. Then, a graphene reflective cell is examined to demonstrate that the reflection coefficient can be controlled by changing the chemical potential and size of the graphene patch. Next, the sectored circular reflective surface is realized with the graphene reflective cells that are properly sized, arranged, and biased to satisfy the required reflection coefficients for various modes of vortex radio waves. Finally, the graphene reflectarray is excited with a horn antenna, showing from simulations that it can be dynamically reconfigured to generate the 0, ±1, and ±2 modes of vortex radio waves at 1.6 THz.

Generation of THz wave with orbital angular momentum by graphene patch reflectarray

A graphene patch reflectarray is proposed for the first time to generate THz wave with orbital angular momentum (OAM). It is shown that by properly assigning the graphene patches with specific reflection coefficients, an OAM-carrying beam can be generated. The graphene reflectarray, which consists of 8 regions and each region contains about 170 patches with uniform chemical potential and size, has successfully produced the OAM-carrying beam of either 1 or -1 mode.

A Novel Tunable Microstrip Patch Antenna Using Liquid Crystal

This paper presents a novel tunable microstrip patch antenna using liquid crystal. It adopts a differentially-driven, aperture-coupled, and stacked-patch structure. Compared with the conventional design, this novel antenna achieves a larger frequency tuning range, much wider impedance bandwidth, higher radiation efficiency and gain. Besides, the novel antenna facilitates the bias design as the bias signal is naturally isolated from the RF signal. Both the conventional and novel antennas are designed to operate at 28 GHz using an RT/Duroid 5880 substrate and K15 liquid crystal. Results show that the novel antenna has a tuning range of 3.1%, an impedance bandwidth of 6.43%, a peak radiation efficiency of 70%, and a peak realized gain of 6.5 dBi, while the conventional antenna has the tuning range of 2.7%, impedance bandwidth of 3.57%, peak radiation efficiency of 45%, and peak realized peak gain of 4.5 dBi.

A Sinusoidally-Modulated Leaky-Wave Antenna With Gapped Graphene Ribbons

This letter proposes a new sinusoidally-modulated graphene leaky-wave antenna for beam scanning at terahertz (THz) with only one biasing voltage required. The antenna consists of a number of dc-gated graphene ribbons on a grounded dielectric substrate. The graphene ribbons are nonuniformly gapped to realize a sinusoidally-modulated reactance surface to support the leaky-wave operation. The analysis shows that the beam angle and leakage rate can be controlled by the gate voltage, indicating a good reconfigurability. The simulated and analytical results agree well with each other that not only validate the design method but also show that the new antenna is promising for graphene-based THz wireless systems.

Tunable terahertz resonator based on intercalation doped-multilayer graphene ribbon (ID-MGR)

Graphene has been proved to be a promising candidate nanomaterial for tunable electronics. In this paper, a novel tunable terahertz resonator is proposed based on an electrically biased intercalation doped-multilayer graphene ribbon (ID-MGR). The induced self-heating effect is taken into account. Then, the equivalent circuit parameters are predicted. The resonant frequencies and Q-factors of the resonator are calculated with the equivalent single conductor (ESC) model. By properly selecting the geometry of the ID-MGR resonator and applying a biasing voltage of 1.0 V, a tuning ratio up to 21.2% can be achieved with the unloaded Q-factor around 25 for the resonant frequency around 1 THz.

Theoretical analysis of a reflected plate for OAM mode generation based on phase-shifting surface

This paper provides a succinct and feasible theoretical analysis of a reflected plate for the generation of orbital angular momentum (OAM) mode. The plate is formed by several sectors with specific reflection phases. The Ansoft HFSS simulated results agree well with those with the proposed theory.

Design of switched-beam antenna for 60 GHz portable devices

This paper reports a compact switched-beam antenna module for 60 GHz portable devices. Two microstrip grid array antennas and two quasi-Yagi antennas are integrated on a 10 mm×10 mm×0.8 mm FR4 substrate. It supports broadside and end-fire radiations. All antennas achieve 7-GHz impedance bandwidth from 58 GHz to 65 GHz, 8.4-dBi gain in the broadside direction and 4.9-dBi gain in the end-fire direction.

A broadband graphene absorber with double Minkowski loops

A graphene absorber is proposed using frequency selective surface (FSS) and resistive graphene strips on a grounded dielectric slab. The FSS unit is based on two concentric Minkowski loops. The simple circuit model indicates that the combination of loops with different substrate thicknesses can be utilized to realize two adjacent absorption bands. Then, the inner loop is located within the middle groove of each unit so as to broaden the overall absorption band. Compared with the graphene absorber using double square loops, the proposed structure has a dramatically enhanced bandwidth of over 45 GHz with the absorption rate larger than 0.9, which has been demonstrated by the full-wave simulations. The low-band absorption is also stable to the oblique incidence.

A beam-steering array using liquid crystal phase shifter

A beam-steering array operating in the 28-GHz band is described, including a 1-by-4 patch antenna array, liquid crystal (LC) based microstrip meander line phase shifters and feeding networks. The RF signal is coupled to the patch antenna array from the slots in the ground plane. The LC phase shifters are implemented in a kind of inverted microstrip line (IMSL) topology by filling liquid crystal between two RT/duroid 5880 substrates(εr = 2.2, tanδ = 0.0009) with a figure-of-merit of 45.2°/dB at 28 GHz. Simulation results of the scattering parameters and the radiation patterns of the antenna are presented and discussed here.

Theory of Reflective Phase-Shifting Surface for Generating Vortex Radio Waves

A theory mainly based on physical optics is developed to analyze reflective phase-shifting surfaces (PSSs) for generating vortex radio waves. The theoretically calculated radiation patterns and phase fronts closely agree with those simulated from a high-frequency structure simulator for the circular disk and annular ring reflective PSS with various dimensions. This theory enables the computation of these surfaces with high efficiency, which indicates its potential for the rapid design and optimization of this important type of surfaces.