everything RF recently interviewed Anouk Hubrechsen who is the CEO of ANTENNEX B.V., a company that develops and sells antenna measurement systems for integrated antennas. She obtained her PhD and MSc degrees in 2023 and 2019, respectively, from the Eindhoven University of Technology, Eindhoven, The Netherlands, where she is now a guest researcher. Her research is focused on antenna measurements in reverberation chambers.
Q. Can you give a brief overview of ANTENNEX? What does the company do and how did you get started on this interesting and innovative concept?
Anouk Hubrechsen: ANTENNEX is a company that develops and sells antenna measurement systems. We focus on testing systems where the antenna and RF electronics are integrated. Having antennas integrated can change the behavior of RFICs (e.g. PA loading in phased arrays, or creating noise mismatching in LNAs), and this level of integration is only increasing. Think of systems on chip, or antennas integrated in the package. This is precisely where the problem lies: with an antenna integrated, many tests that were previously performed in a conducted manner, now need to be performed wirelessly.
Generally, wireless tests are performed in an anechoic chamber. They test a single direction at the time, typically with some form of mechanical scanning to obtain a full pattern from which a received or radiated Power Spectral Density can be extracted. Scanning takes time, but for a passive antenna with about 10 test cases this is within an acceptable time of a few hours. Now take an RFIC, and the number of test cases can easily get in the order of thousands – testing a 64-element phased array can take over a week, at that is already limiting the number of test cases for just a few hundred. (Note that we are not even speaking about production testing here, which gives rise to a whole new set of problems). To make matters worse, these tests can have a high measurement uncertainty, especially at millimeter wave frequencies, where it can sometimes take several months to interpret the testing results – an unacceptable delay in the fast-paced semiconductor industry.
The test and measurement industry needs to keep up with the fast innovations that are happening, but the testing requirements have changed so much over the last years, that optimizing existing systems just won’t do the job anymore. The concepts behind testing need to be rethought from scratch to solve the testing time problem. With this philosophy, we started our company ANTENNEX.
Q. Can you tell us about your Wireless ConnectorTM and how it works? How does this device simplify conducting OTA antenna measurements?
Anouk Hubrechsen: The concept behind all our products is what we call ‘The Wireless Connector™’, named this way because it can be seen as the wireless equivalent of a coaxial connector. This hints to what measurements are possible, but also to the ease of use. The system is a hardware platform on which continuously new hardware and software-based extensions will be released, enabling for new measurements and applications. The current operational frequency is up to 140 GHz.
The technology we use is grounded in a reverberation chamber. The inside is fully metallic and, in many ways, can be seen as the dual of an anechoic chamber. Instead of mechanical scanning, we change the electromagnetic environment around the device using metallic paddles and sample the fields for different positions of the paddles. Changing the environment ensures that the device under test can be placed almost anywhere in the chamber. This removes the sensitivity to antenna positioning, making it much easier to use and making the results more reliable as positioning is a large source of uncertainty in anechoic chambers. This process works for both Tx and Rx testing. This mode of operation also speeds up measurement time (e.g. the total radiated PSD of a 77 GHz FMCW radar in chirp mode can be tested over 4 GHz within a second within +/- 0.2 dB uncertainty). It should be noted that the metal interior inherently causes some radiated power to return to the DUT. However, athis is due to our patented technology in the order of -30dB, which is typically lower than mutual coupling in a phased array.
Because all information remains inside the chamber, it is possible to evaluate it such that the user gets not only the measured result, but also the measurement uncertainty. We can use the measurement data to perform automatic measurement diagnostics that save a significant amount of time in evaluating the measurement. The product can test metrics related to overall received or radiated power, such as radiated power spectral density, metrics related to compression of PAs and LNAs, ACLR, PAE, PAPR, IM products, OoB emissions, time-varying spurious, receiver gain, NF, FMCW spectrogram, FMCW chirp linearity.
Q. What are some of the challenges that occur while testing integrated antennas and RFICs? How does OTA measurement contribute to overcoming these challenges?
Anouk Hubrechsen: When antennas are integrated with an RFIC in e.g. a phased-array system, the test can oftentimes only be performed wireless. Because of the number of tests cases, it is typical to evaluate many metrics for a single direction, whereas many effects such as a reduction in efficiency due to PA loading are better reflected in the overall radiated power (the integral over all directions) because no assumption on the antenna’s directivity has to be made. Testing a single direction inherently misses important effects (e.g. in a phased array system a harmonic may radiate towards a completely different direction in comparison to the carrier). The dependence on direction can give a high uncertainty due to potential errors arising from: DUT placement, knowing the direction of the main beam, knowing the directivity, and in placing the reference antenna correctly per beamforming setting.
Q. Can you share some unique test cases where MAAX has helped in conducting complex OTA measurements with ease?
Anouk Hubrechsen: A most recent test case was an E-band FMCW radar test case, where we tested a few GHz of total radiated PSD within seconds with +/- 0.2 dB uncertainty and evaluating chirp linearity and out-of-band components at the same time. The test is complex to do over the air, as there is a time dependence due to chirping, and a spatial dependence because direction of radiation changes per frequency. The chamber removes both dependencies when using it with a time-domain-based detector such as an oscilloscope. With our API, the oscilloscope and chamber can be synchronized, and it includes automatic post-processing.
When integrated with a spectrum analyzer, it can be used to analyze millimeter wave phased arrays up to 140 GHz. It can be used to evaluate effects of LO leakage and other out-of-band effects, or to quickly evaluate the differences between channels, paths of the array of DUTs. These tests are useful for clients developing these arrays for applications such as PtMP links and radar.
Another example of a testing capability that has been used by several clients but that is to be released is over-the-air tests of noise figure up to 140 GHz. The chamber can be used as a very repeatably wireless noise source with a tunable ENR, which is useful in e.g. testing the noise figure of a phased array for different beam settings.
Q. Can you tell us more about the software and API solutions that are integrated into the wireless connector that help in a seamless and easy measurement process?
Anouk Hubrechsen: The API can be used to fully control and automate the measurement process. The API can be used in Python and MATLAB, and we provide easy to use example scripts to perform various types of measurements. The control of the DUT or instrumentation can be implemented in the example scripts, and we provide online or on-site support to make sure that everything works. Certain vendor-specific instruments are already integrated in the example scripts. The API integrates measurement processing algorithms which automatically gives the user the measurement results and the corresponding uncertainty level.
Q. What all antenna / OTA parameters can be measured using MAAX at the moment? Do you plan to enable the measurement of Noise Figure and Radiation Pattern as well? When can users expect this?
Anouk Hubrechsen: The supported measurements are: radiated power spectral density, metrics related to compression of PAs, ACLR, PAE, PAPR, IM products, OoB emissions, time-varying spurious, FMCW spectrogram, FMCW chirp linearity. Two capabilities we are very excited about releasing are the noise-figure module and a radiation pattern module. We will release this capability in the near future so make sure to stay tuned.
Q. What market segments do you target, and which segment drives the most business for you?
Anouk Hubrechsen: We mainly target the millimeter-wave segment at this moment, with a few applications mentioned earlier. With the current capabilities of the system, value is mainly added for clients using systems with multiple antennas (e.g. phased-array antennas, or MIMO systems).
Q. Who are some of your customers and where are they located? Can you give us a percentage of geographical breakup by continent?
Anouk Hubrechsen: The system has just entered the market and we are delivering the first systems in Q3 of this year. Our company has a team that is European and US based, which is also where most our clients are currently located.
Q. What is the 3-year product roadmap for ANTENNEX ?
Anouk Hubrechsen: In the upcoming three years, we will mainly focus on extending our capabilities for automating measurements. That is, extracting as much information out of the chamber in the shortest time to maximize the number of test cases without compromising on accuracy. These will be extensions to the existing hardware platform that are to be released, such as a noise-figure module for noise figure or interference testing, or a module that enables obtaining more information about a radar.
