Reconfigurable Intelligent Surfaces for Wireless Communications: Principles, Challenges, and Opportunities

Recently there has been a flurry of research on the use of reconfigurable intelligent surfaces (RIS) in wireless networks to create smart radio environments. In a smart radio environment, surfaces are capable of manipulating the propagation of incident electromagnetic waves in a programmable manner to actively alter the channel realization, which turns the wireless channel into a controllable system block that can be optimized to improve overall system performance. In this article, we provide a tutorial overview of reconfigurable intelligent surfaces (RIS) for wireless communications. We describe the working principles of reconfigurable intelligent surfaces (RIS) and elaborate on different candidate implementations using metasurfaces and reflectarrays. We discuss the channel models suitable for both implementations and examine the feasibility of obtaining accurate channel estimates. Furthermore, we discuss the aspects that differentiate RIS optimization from precoding for traditional MIMO arrays highlighting both the arising challenges and the potential opportunities associated with this emerging technology. Finally, we present numerical results to illustrate the power of an RIS in shaping the key properties of a MIMO channel.Comment: to appear in the IEEE Transactions on Cognitive Communications and Networking (TCCN

Dielectric Resonator Reflectarray Antenna Unit Cells for 5G Applications

This paper presents an investigation for the performance comparison of three different unit cell configurations operating at 26 GHz for 5G applications. The unit cells are cross shape dielectric resonator, cross microstrip patch and cross hybrid dielectric resonator. Verification of the comparison has been done by simulations using commercial Computer Simulation Technology Microwave Studio (CST MWS). The simulated results for reflection phase, slope variation, reflection loss and 10% bandwidth were analyzed and compared. The results indicate that the optimum configuration to be deployed for the reflectarray’s unit element in order to fulfill the 5G requirements of a wide bandwidth is the cross hybrid DRA. This configuration is a combination of cross DRA with cross microstrip patch as the parasitic element in order to tune the phase and provide a wide phase range with smooth variation slope. Cross hybrid DRA provided a wide phase range of 520° with 0.77 dB loss and 10% bandwidth of 160 MHz

Additively Manufactured Shape-changing RF Devices Enabled by Origami-inspired Structures

The work to be presented in this dissertation explores the possibility of implementing origami-inspired shape-changing structures into RF designs to enable continuous performance tunability as well as deployability. The research not only experimented novel structures that have unique mechanical behaviour, but also developed automated additive manufacturing (AM) fabrication process that pushes the boundary of realizable frequency from Sub-6 GHz to mm-wave. High-performance origami-inspired reconfigurable frequency selective surfaces (FSSs) and reflectarray antennas are realized for the first time at mm-wave frequencies via AM techniques. The research also investigated the idea of combining mechanical tuning and active tuning methods in a hybrid manner to realize the first truly conformal beam-forming phased array antenna that can be applied onto any arbitrary surface and can be re-calibrated with a 3D depth camera.Ph.D

Low Power Reconfigurable Antenna with Continuous Beam Steering Capability

Each year, the number of wireless devices increases, and the size of the devices’ data is increases, 8k video streaming, for example. More and more bandwidth is needed for wireless networks to meet these growing demands. Higher frequencies allow for more bandwidth; however, using higher frequencies comes with some trade-offs. The higher the wireless signal frequency, the shorter the distance it can travel before the signal strength becomes too weak for the receiver to pick it up. One solution might be to increase the power of the signal provider, but that would waste a lot of energy. Most antennas radiate in all directions, so a lot of that extra power would be going up to space, or just away from the device it’s trying to connect with, or it could be picked up as noise by a device on a different network. Instead, in many areas of research, including the research presented here, the issue is addressed by creating a better antenna. This research presents an antenna that focuses its radiated energy into a beam towards the target device. Focusing the power towards a device increases the signal’s power going towards that device without much power going in undesired directions. If the target device moves, then the beam needs to be steered, so it keeps pointing at the device. The ability for an antenna to change something like the direction of its beam makes the antenna a reconfigurable antenna. Some reconfigurable antennas only have a few beam directions to choose from, so they would have to pick the closest one to the target device. The beam can be steered smoothly through any horizontal direction between two limits for this research. This research uses less power and fewer components to do so compared with some previous works

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Systematic Framework for Reflectarray Synthesis Based on Phase Optimization

A new systematic synthesis framework for reflectarray antennas is discussed. Optimization based on the Levenberg-Marquardt algorithm is used to obtain the phase distribution of the reflection coefficients required on the reflectarray surface, in order to achieve the pattern specifications. A Local Multipoint Distribution System (LMDS) base station working in the 24.5–26.5 GHz frequency band has been proposed to evaluate the method. The 3D requirements are defined by the combination of the elevation and templates and considering a maximum acceptable ripple in the beam shaping. Some illustrative results are obtained