Coming in from the cold

Cambridge engineers have imported a technique from Siberia to achieve a
breakthrough in measuring high-frequency electronic systems. Jon Excell reports.

UK researchers have drawn on cold war era Russian military technology to develop a groundbreaking technique for measuring the properties of microwave materials that are used in the design of high- frequency systems. The technique will be invaluable in the design of much anticipated high-frequency electronic systems such as 77GHz car anti-collision radars, claimed its developer, Cambridge-based technology company Generics.

Project leader Mick Mclean explained that high frequency designs call for thinner and thinner substrates (such as those used in printed circuit boards). And to optimise circuit design, accurate measurement of the electrical properties of these substrates becomes increasingly important. These properties, which include, for instance, the way the substrate behaves as an insulator, vary according to frequency – hence the importance of accurate measurement.

Until now measuring these parameters at high frequencies has simply not been possible, and designers have attempted with limited success to apply test methods typically used at much lower frequencies. One traditional method is to make a test structure on a circuit board to measure the parameters. But this approach is expensive , time-consuming and becomes increasingly impractical at higher frequencies. But Mclean’s team has an easy-to-use, low-cost process for high-frequency measurement where you can simply ‘snip a bit off and slip it in a machine’. Researchers around the world, including a group at the National Institute of Standards and Technology (NIST) in the US, have been trying to do this for years and never quite succeeded.

Generics’ breakthrough came when it discovered that engineers from the Siberian Research Institute had pioneered a lab-based dielectric resonance system, which although not very user-friendly, would work at high frequencies.

The system is based on sapphire discs arranged in a ‘whispering gallery’ configuration. This configuration enables the generation of an electromagnetic field that can be used to measure a substrate’s properties far more thoroughly than is possible with traditional techniques.

Generics set about developing the technology for the production line. ‘People told us [we needed] something we could use to take samples off the production line, because batches of PCB material vary by five to 15% from batch to batch,’ he said.

The current test rig has been designed to analyse electronic systems that operate at 40GHz. This, said Mclean, is the anticipated operating frequency of next-generation wireless point-to-point links. However, he added that it will be relatively easy to scale the system up or down for other frequencies as they emerge.

The frequency range you can measure is determined by the size of the sapphire discs being used as resonators: for a higher-frequency system you have to have smaller discs. Thus, while it is not possible to make a universal system that can deal with different frequencies at the flick of a switch, Mclean’s team is looking into redesigning the machine so the discs are interchangeable, making it more or less frequency independent. The firm is trying to gain more DTI funding to put these ideas into practice.

However, while the technique may be ready for the factory floor, it appears that the factory floor isn’t quite ready for the technique. Mclean explained that when the project began Generics already had two or three interested parties but then the recession came along and prospective users put their R&D on ice.

Nevertheless, he is confident that it won’t be long before the system finds its first commercial application. ‘Over the next year or two people will start to revive design projects for those high-frequency systems for which it was designed. There will be enough of a recovery in the remnants of the telecoms industry to make it all worthwhile,’ he concluded.

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