Optically tunable microwave antennas for 5G applications

Simulated surface currents on a slotted microstrip patch with illumination of a silicon superstrate University of Bristol

4.2GHz – 6 GHz optically tunable cavity backed slot antenna. Silicon samples can be seen in the slot and an optical fibre is being held in place over one sample for tuning University of Bristol

Press release issued: 15 November 2017

Multiband tunable antennas are a critical part of many communication and radar systems. New research by engineers at the University of Bristol has shown significant advances in antennas by using optically induced plasmas in silicon to tune both radiation patterns and operation frequency.

Conventional antenna tuning is performed with diodes or Micro-Electro-Mechanical Systems (MEMS) switches. However, these approaches have significant drawbacks as systems become more complex and move to higher frequencies, which is anticipated for 5G systems.

The first paper, published in IET Optoelectronics, co-authored by Dr Chris Gamlath, Research Associate in RF Engineering during his PhD, shows how a silicon superstrate placed over a slotted microstrip patch can be used to tune radiation patterns.

The second paper published in IEEE Transactions on Antennas and Propagation, co-authored by Dr Michael Collett during his PhD, demonstrates how silicon can be placed within the slots of an air-spaced, cavity-backed antenna to perform frequency and pattern tuning that achieves high efficiencies.

The research could dramatically improve the performance of future communication and radar systems because without this technology, it may not even be possible to implement certain types of 5G systems.

Martin Cryan, Professor of Applied Electromagnetics and Photonics in the Department of Electrical and Electronic Engineering at the University of Bristol and co-author on the papers, said: "This technology relies on the interaction between light and a semiconductor such as silicon. When the semiconductor is illuminated by an appropriate wavelength of light, the photons generate electrons and holes which increase the conductivity in the silicon creating a "metal-like" region. Microwave signals can then interact with these conductive regions and with correct design, tunable antennas and circuits can be created.

"One major advantage of this approach is that no physical connection to the silicon is required, unlike diodes or MEMS switches that require complex DC Biasing circuits. This can dramatically simplify the design of multi-element antennas, which are required in Multiple-Input Multiple-Output (MIMO) systems and phase array radars. There is a requirement for lasers or LEDs to be used within the system, but the cost and performance of these have improved significantly in recent years."

Professor Cryan's research team is now working on moving to millimetre wave (>30GHz) frequencies and to very high power levels where this technology will again out-perform existing technologies.

Papers:

'Investigation of an optically induced superstrate plasma for tuning microstrip antennas' by Chris Galmath et al in IET Optoelectronics

'An optically tunable cavity-backed slot antenna' by M. A. Collett, C. D. Gamlath, and M. J. Cryan in IEEE Transactions on antennas and propagation

Further information

Professor Cryan works in the Photonics and the Communications Systems & Networks (CSN) research groups in the Department of Electrical and Electronic Engineering, part of the School of Computer Science, Electrical and Electronic Engineering, and Engineering Maths

Dr Collett's PhD was funded by the EPSRC Centre for Doctoral (CDT) Training in Communications in the Department of Electrical and Electronic Engineering.

About the EPSRC Centre for Doctoral Training (CDT) in Communications
The EPSRC Centre for Doctoral Training (CDT) in Communications is a state-of-the-art environment for training postgraduates to lead innovative research, future product development and exploitation.

The Centre will help to build UK capability in communications engineering by addressing the skills shortage in the sector. It will focus on Future Communications: People, Power and Performance; while communications technology is the enabler, the Centre recognises that it is people who are the creators, consumers and beneficiaries in terms of its broader applications.