A low loss active RIS reconfigurable surface for 6G antennas
Researchers from the UK and Ireland are developing a low loss active reconfigurable intelligent surface (RIS) for the next generation of indoor 6G antennas.
6G will include high frequency millimetre and terahertz signals that have a short range and so require repeaters and amplifiers.
Engineers from the University of Glasgow are working with the Tyndall National Institute’s Wireless Communications Laboratory (WCL) on the three-year Active intelligent Reconfigurable surfaces for 6G wireless COMmunications, or AR-COM, project, with £1.5m of funding..
The design, which the project calls an Intelligent Reconfigurable Surface, aims to have little or no loss or latency to act as repeaters and amplifiers. The aim is to use low powerresonant tunnelling diodes (RTDs) with transition metal oxides (TMOs) that act as DC-controllable ultra-fast switches and phase shifters.
This will have the capability to both alter the phase and amplitude of the incident signal and compensate for the incident signal loss incurred through traversing the RIS through the amplification by the RTDs.
A standard for RIS materials is in development at European group ETSI.
“Current materials used in wireless communications face significant limitations, especially at the higher frequencies that 6G networks will require. With AR-COM, we’re building on the expertise of the University of Glasgow and the Tyndall Institute with the support of key industry partners to develop truly next-generation technologies,” said Professor Qammer H. Abbasi, Director of the Communications, Sensing and Imaging (CSI) hub at the University of Glasgow’s James Watt School of Engineering and the AR-COMS’s principal investigator.
The first objective of the project is to develop TMO-based switches for the control of amplitude of the signals incident on the RIS. The team will develop TMO-based switches using either VO2 or TiO2 for material design, growth realization, and characterization of binary and mixed/doped metal oxides. They will employ both thermal and plasma-assisted atomic layer deposition to engineer materials with controlled stoichiometry and defect levels.
The second objective is to develop TMO-based phase shifters for the control of the phase of the incident signal on the IRS. The team will investigate the idea for phase shifting of a propagating wave interlaced with sub-skin depth metal TMO/insulator structures. They will examine the fundamental limits of the ‘single-bit’ insulator/TMO/insulator stack and its performance as a function of the TMO type, their switching mechanism, thickness, characteristics of the dielectrics, biasing lines, and the frequency of operation.
The third objective is to develop RTD reflection amplifiers to compensate for the losses in the circuitry of the IRS and offset the high path loss at terahertz (THz) frequencies above 100GHz. This will use the RTD’s negative differential resistance to amplify the input signal before it is reflected back. Microwave RTD low noise reflection amplifiers have already been demonstrated featuring very low power with 10 dB gain at 5.7 GHz. The feasibility of such amplifiers at K and Ka band frequencies with 100 µW level DC power consumption and a high gain of 32 dB has also been recently demonstrated.
These will be combined to create a RIS capable of controlling the amplitude and phase of incident signals with no or very low loss and low latency.
“Resonant tunnelling diodes, which can amplify signals while using very little power, and transition metal oxides which can act as ultra-fast switches have a great deal of potential to help overcome the bottlenecks of current generations of IRS technologies. Together, these technologies will help us create surfaces that not only redirect signals but also boost them with minimal energy consumption, which will help them find use in a wide range of devices in the years to come,” said Dr Senad Bulja who leads Tyndall National Institute’s contribution to AR-COM
Professor Muhammad Imran, project co-investigator and the head of the James Watt School of Engineering, said: “Intelligent reconfigurable surfaces will be key to solving the challenges of delivering robust 6G networks and enabling the next generation of wireless applications. Ultrafast, ultra-low latency wireless networks will underpin new forms of communication and sensing that will transform how we interact with each other in the years to come.”
Tyndall’s WCL, based at University College Cork, was founded in 2020 by three former scientists from Nokia Bell Labs – Holger Claussen, Lester Ho and Senad Bulja – to boost Tyndall’s research activities in the communications space.
www.glasgow.ac.uk; www.tyndall.ie
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