There is a rapid increase in (smart) devices that are or will be connected to the 5G network. The high-frequency antennas embedded in these are often integrated with chips, which makes testing a lot more difficult. TU/e researcher Anouk Hubrechsen went to work with a concept from acoustics and shows that her unique table-top reverberation chamber can measure high-frequency antennas much more accurately and quickly.

Anouk Hubrechsen in the reverberation chamber. Photo: Bart van Overbeeke

Anouk wrote her thesis as a practical guide, and meanwhile, as CEO of spin-off Antennex, is convincing more and more companies to use this new measurement method.

Making antennas for 5/6G systems is already no sinecure, because chips are often integrated, but measuring them through is almost impossible. Because whereas you normally measure a chip by connecting it, now the quality requirements have to be determined with the antenna attached. You can't just connect that with a cable; the electromagnetic waves travel through the air. And so chips also have to be measured 'through the air'. Moreover, all those hundreds of antennas have to be tested, in different settings, in which they can influence each other - unintentionally.

"I like a challenge," says Anouk Hubrechsen in an interview with Cursor. With a successful result, because thanks to a new measurement method, she managed to measure high-frequency antennas accurately and quickly at many points. She recently defended her thesis cum laude at the Faculty of Electrical Engineering.

Bottleneck test capacity

Current antennas are generally tested in an anechoic chamber: a room in which the walls absorb all echoes. Both the set-up and interpretation of the measurement data here are time-consuming and require a lot of expertise.

"Many companies spend more than a third of their development time measuring through their antennas," she stresses. "There are more and more 5G applications, every device has to be tested. We are really running into a bottleneck in terms of testing capacity."

Reflecting all waves

So things have to change course, Hubrechsen believes, which is why she researched an entirely different measurement chamber within TU/e's antenna measurement group: a 'reverberation chamber' with metal walls that actually reflect all the waves.

  • the reverberation chamber concept has been around for a long time and comes from the acoustics corner. Only we don't work with sound waves, but with electromagnetic waves.
  • the reflections allow us to mimic reality much better. Moreover, it allows you to capture all the energy emitted by the antenna in a much shorter time.
  • in conventional measurement systems, you have to mechanically scan the room point by point and eventually merge everything, in a reverberation chamber everything is measured in one go.
  • it is also easier to measure whether a device is radiating at the right frequency and whether the maximum is not exceeded, as is important for mobile phones, for example.
  • for certain quality aspects of antennas, this method is therefore much more accurate, scalable and up to a hundred times faster.

Open mindset

A prototype reverberation chamber was built to specifically measure high-frequency antennas, an extensive validation process by Hubrechsen followed. A piece of pioneering work, she acknowledges after some urging.

"When I started my PhD project, I was working in the first reverberation chamber capable of such a high frequency. I saw many different sides of this chamber and found out many problems step by step through all those measurements. And gradually discovered how to solve them. By looking with an open mindset, and sticking less to a stochastic process in which models are sometimes used blindly, we were able to make the translation into an actual product."

Practical handbook

Although the results of Hubrechen's work show that the reverberation chamber offers many advantages over current measurement techniques, she still faces hesitant researchers. She says this is because in a reverberation chamber, the antenna direction is more difficult to determine than in a dead room, whereas for high-frequency antennas that bundle their beams for a strong signal, that direction is important.

Antenna direction

However, she shows that for many measurements the antenna direction is less important than assumed. For measurements in which it does matter, she and her reverberation chamber colleagues developed a new methodology. To convince people now of the power of the reverberation chamber for measuring the latest properties of antenna systems - antenna as well as electronics - she decided to write her thesis as a practical handbook and show all the ins and outs. "The technology behind the reverberation chamber is harder to understand. Something that is more intuitive is more trusted. Then I just have to show it. Because when people experience for themselves how well it works they are converted."

And she is now seeing that with more and more users, including at Antennex, the first company to market a handy high-frequency model reverberation chamber for corporate use.

Response

Ernst wrote:
Would also be nice if this measurement method were also legally accepted.
Getting this done may be more difficult than the technical challenges