News Feature | November 17, 2017

University of Bristol Makes Optically Tunable Microwave Antennas For 5G Networks

By Jof Enriquez,
Follow me on Twitter @jofenriq

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. Image courtesy of University of Bristol

Microwave antennas can be tuned successfully through interaction of light with silicon in order to meet the demand for increasing operating bandwidth and higher efficiencies promised by 5G communication networks, according to researchers at the University of Bristol.

Antenna design is an important component to guarantee the signal distribution of higher frequency bands for high-capacity 5G wireless systems. Micro-Electro-Mechanical Systems (MEMS) switches used to tune current antennas, however, have several limitations that make them less ideal to operate under 5G networks using higher frequency bands.

With 5G looming, antenna design engineers are under pressure to test newer types of antennas that are configurable — that is, have the ability to not only control the bandwidth, but also the radiation pattern and polarization pattern, while using power and spectrum efficiently.

To this end, engineers at the University of Bristol are investigating two similar methods to improve current multi-band tunable antenna design by using miniature lasers to interact with silicon components incorporated in the antenna

The first paper explains the design for an antenna that can generate optically induced electron–hole plasmas in silicon to perform radiation pattern tuning. This new type of antenna uses a silicon superstrate placed in "a slot loaded microstrip patch and the effect of illumination is shown to produce beam switching in the radiation patterns of certain modes while other modes are left unaffected," wrote the researchers, Chris D. Gamlath, Michael A. Collett, Weiran Pang, David M. Benton, and Martin J. Cryan, in IET Optoelectronics.

"This technology relies on the interaction between light and a semiconductor such as silicon," said Cryan, who is Professor of Applied Electromagnetics and Photonics in the Department of Electrical and Electronic Engineering at the University of Bristol.

"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," he adds.

The second paper, meanwhile, describes an optically tunable cavity backed slot antenna, consisting of "four silicon bridging pieces and a fiber coupled laser" to successfully tune the operating frequency between 4.2 and 6 GHz, according to co-authors Gamlath, Collett, and Cryan, in IEEE Transactions on Antennas and Propagation.

"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," says Cryan.

He and his colleagues will next test their reconfigurable antennas to operate in millimeter wave (>30GHz), which is also known as extremely high frequency (EHF), or very high frequency (VHF) by the International Telecommunications Union (ITU).