Graphene for Antenna Applications: Opportunities and Challenges from Microwaves to THz

The use of graphene for antennas and other electromagnetic passives could bring significant benefit such as extreme miniaturization, monolithic integration with graphene RF nanoelectronics, efficient dynamic tuning, and even transparency and mechanical flexibility. Though recently different related theoretical works have been presented, relatively few applications have been proposed and realistically assessed. In this invited talk we will briefly review the main properties of graphene and the state of the art in its theoretical and experimental characterization. Then, we will discuss a number of potential antenna applications from microwave to THz, providing in each case a critical assessment of the benefits, limitations, and remaining issues towards actual real-life implementations. Here we provide a brief overview of different devices and associated developments in our group discussed in the talk, including graphene antennas and reflectarrays at microwave and THz, plasmonic switches, isotropic and anisotropic meta-surfaces, or graphene RF-NEMS

MEMS-reconfigurable metamaterials and antenna applications

This paper reviews some of our contributions to reconfigurable metamaterials, where dynamic control is enabled by micro-electro-mechanical systems (MEMS) technology. First, we show reconfigurable composite right/left handed transmission lines (CRLH-TLs) having state of the art phase velocity variation and loss, thereby enabling efficient reconfigurable phase shifters and leaky-wave antennas (LWA). Second, we present very low loss metasurface designs with reconfigurable reflection properties, applicable in reflectarrays and partially reflective surface (PRS) antennas. All the presented devices have been fabricated and experimentally validated. They operate in X- and Ku-bands.Comment: 8 pages; 8 figures; International Journal of Antennas and Propagatio

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.Comment: 16 pages, 12 figure

User Effects in Beam-Space MIMO

The performance and design of the novel single-RF-chain beam-space MIMO antenna concept is evaluated for the first time in the presence of the user. First, the variations of different performance parameters are evaluated when placing a beam-space MIMO antenna in close proximity to the user body in several typical operating scenarios. In addition to the typical degradation of conventional antennas in terms of radiation efficiency and impedance matching, it is observed that the user body corrupts the power balance and the orthogonality of the beam-space MIMO basis. However, capacity analyses show that throughput reduction mainly stems from the absorption in user body tissues rather than from the power imbalance and the correlation of the basis. These results confirm that the beam-space MIMO concept, so far only demonstrated in the absence of external perturbation, still performs very well in typical human body interaction scenarios.Comment: 4 pages, 7 figures, 2 table

Further Comment on 'Encoding many channels on the same frequency through radio vorticity: first experimental test'

We show that the reply by Tamburini et al (2012 New J. Phys. 14 118002) to our previous comment (2012 New J. Phys. 14 118001) on the experiment reported in (2012 New J. Phys. 14 033001) actually does not invalidate any of the issues raised in our initial comment.Comment: 3 pages, 1 figur

Polarimetric Control of Reflective Metasurfaces

This letter addresses the synthesis of reflective cells approaching a given desired Floquet's scattering matrix. This work is motivated by the need to obtain much finer control of reflective metasurfaces by controlling not only their co-polarized reflection but also their cross-coupling behavior. The demonstrated capability will enable more powerful design approaches -involving all field components in phase and magnitude- and consequently better performance in applications involving reflective metasurfaces. We first expose some fundamental theoretical constraints on the cell scattering parameters. Then, a successful procedure for controlling all four scattering parameters by applying parallelogram and trapezoid transformations to square patches is presented, considering both normal and oblique incidence

Manipulation of Giant Faraday Rotation in Graphene Metasurfaces

Faraday rotation is a fundamental magneto-optical phenomenon used in various optical control and magnetic field sensing techniques. Recently, it was shown that a giant Faraday rotation can be achieved in the low-THz regime by a single monoatomic graphene layer. Here, we demonstrate that this exceptional property can be manipulated through adequate nano-patterning, notably achieving giant rotation up to 6THz with features no smaller than 100nm. The effect of the periodic patterning on the Faraday rotation is predicted by a simple physical model, which is then verified and refined through accurate full-wave simulations.Comment: 4 pages, 5 figures, submitted to Applied Physics Letter

Microwave periodic structures based on MicroElectroMechanical Systems (MEMS) and micromachining techniques

As a result of the ever growing number of functionalities and standards to be supported by communication systems, as well as the constant development of radar and imaging technologies, a key research area in the field of microwaves and millimeter waves is the achievement of reconfigurability capabilities. In recent years, the progress of MicroElectroMechanical Systems (MEMS) fabrication techniques has allowed radically challenging the performances of reconfigurable devices based on established technologies such as controllable ferrite material, semiconductor pin diodes or FET transistors. Consequently, there is presently significant effort to apply MEMS technology to the microwave field; in the case of high-cost applications (e.g. radars, satellites), the main reason is the state-of-the-art performances that MEMS technology can offer; namely, low losses, high linearity, large bandwidth. In the case of mass market (e.g.: mobile phone, GPS receiver), it is rather pushed by the increasing demand for the integration of numerous microwave functionalities into a monolithic, small, low-power consuming and low-cost device. In this context, the objective of this thesis is to contribute to the development of new periodic or cascadable microwave devices reconfigurable by means of MEMS. Indeed, numerous microwave devices take advantage of the particular propagation properties of a wave in periodic structures to achieve given functionalities (e.g. phase shifters, frequency selective surfaces, periodic antennas, antenna arrays and reflectarrays, metamaterials). For this purpose, analysis and design methods were developed based on the theory of waves propagating in periodic structures to help in dealing with different kinds of periodic or cascadable MEMS structures in an integrated approach. The method comprises the following main steps: the setup of efficient full-wave simulations of MEMS blocks, the derivation of physical and accurate circuit models, and the development of hybrid full-wave-circuit model design methods based on periodic structure modeling. It is noticeable that several theoretical developments presented are not restricted to micromachined and MEMS devices, but could be of use for many other microwave designs. Three main classes of devices have been studied and designed to illustrate the versatility of the approach, as well as the various potentialities of MEMS in microwave applications. The first structure addressed is an existing microwave MEMS structure, the distributed MEMS transmission line (DMTL), for which design methods based on the periodic structure modeling were developed. Analog and digital devices were fabricated, showing excellent agreement with the circuit modeled results. We also introduce and analyze a new topology for the reduction of the mismatch in multi-bit DMTLs. The results presented next consist mainly in theoretical developments on the metamaterial composite right/left handed transmission line (CRLH-TL) structure, carried out to overcome the limitations of existing models, which were shown to be inappropriate in the case of MEMS CRLH-TL implementations. Fixed micromachined devices were successfully designed based on the new theory, which also allowed the demonstration of the possibility to design especially low/high impedance CRLH-TLs. Next, MEMS implementations of variable CRLH-TLs are presented. Analog and digital devices were designed, and excellent agreements between full-wave simulations and circuit models are obtained in both cases. For fabrication reasons, only the analog device could be measured to exhibit the expected performances. This constitutes –to the author's knowledge– the first implementation of a MEMS-reconfigurable metamaterial structure. The last device studied is a MEMS-reconfigurable reflectarray cell. A comprehensive assessment of the numerous requirements for such a cell with regard to the functioning of a reconfigurable reflectarray is first presented, as well as detailed discussions on the rigorous simulation and measurement of the device. A monolithic MEMS reflectarray cell was then designed based on these considerations, and exhibits excellent performances in comparison with other reconfigurable reflectarray cells based on MEMS and other technologies