Loss adjuster

A three-year project sets out to use ultraviolet light for a more cost-efficient phase shifter control.


Keeping track of a very fast-moving object can be a matter of life and death, particularly if it’s a missile travelling at up to five times the speed of sound. It may be possible with the human eye from a safe distance but it’s not an easy task for an automated system.

It can be done with an array of electronically-steered antennas, which effectively improve the focus of the signal on the object. It is swept back and forth very rapidly, rather like a searchlight. It sounds straightforward and is already used in military systems. But it has a major drawback that prevents it finding use in more widespread applications — it’s very expensive.

This is because the focusing is done by phase shifters, devices that alter the output signal phase when a voltage is applied. A single ferrite or semiconductor shifter can cost more than £100 and, depending upon the application, some antennas may need up to 1,000. The devices may take up no more room than a unit on a standard computer rack but they are worth far, far more.

A team of engineers is investigating how to reduce the cost significantly. antenna specialists Antenova of Cambridge, and Prof Neil Alford and Dr Peter Petrov of Imperial College London, will spend the next three years honing a novel approach to controlling phase shifters.

The main step will be making them out of relatively low-cost ferro-electric film, which promises to permit devices that will cost just a few pounds each. The trouble is that ferro-electric devices normally suffer from hysteresis so they can’t react quickly enough to maintain optimum control of the phase-shifter.

Fortunately Alford and Petrov recently discovered that when ultraviolet light illuminates a phase shifter made of a thin film of barium strontium tritanate, the hysteresis is suppressed. The lag that would normally take place does not appear.

‘The main aim is to avoid this hysteresis,’ said Alford. ‘The wavelength of the ultraviolet has an energy that corresponds to the energy of the band gap in the base material. That was our reason for trying that particular wavelength in the first place.’

It had been understood for a while that this phenomenon was possible, but the Imperial team, along with colleagues at St Petersburg Electrotechnical University, Russia, showed it could be usefully applied to phase shifters.

Researchers at Birmingham University have corroborated the findings, and now Alford and Petrov are preparing to investigate it further. ‘Suppressing hysteresis is the main benefit but once you start looking at high frequencies you start to see other performance benefits,’ said Alford. ‘Above 10 GHz, which is around the frequency used by satellites, you start to reduce losses.’

With better performance characteristics, transmitter phase shifters will require less power, thus saving energy and reducing electromagnetic radiation. Inter-channel interference will also be reduced.

All of these advantages will be well received by defence systems manufacturers but are there non-military applications for steerable antenna arrays? ‘They could certainly be used in the automotive field, within on-board radar units operating at 70GHz to assist collision avoidance and other driver assistance systems,’ explained Alford. ‘And they may find a place in mobile communications.’

If the project succeeds in perfecting the use of ultraviolet light to suppress hysteresis, Antenova would be the most likely company to commercialise the breakthrough. As a leading developer and supplier of high-performance antennas and RF antenna modules for mobile handsets, portable devices and laptop computers it is in a good position to run with new ideas.

Only last week it secured more than £5m for investment in growth and expansion, and announced the opening of a new US R&D and support centre in Chicago. ‘This additional investment will allow us to accelerate development of our range of RF antenna modules and establish additional design centres to further penetrate and support our target markets,’ said chief executive Greg McCray.

The company recently announced the world’s first single-package GPS, which combines a high-performance and low-power receiver with its high efficiency single ended internally balanced antenna.

‘Our plans are on target for opening locations in Shanghai next quarter, followed by facilities in Korea and Japan by the end of the year,’ said McCray.