As mmWave Tech Matures, T&M Equipment and Techniques are Shifting, Too
While millimeter wave technology is by no means new, test and measurement suppliers are releasing innovative tips and equipment to help test engineers address higher-frequency challenges.
The rollout of 5G has also yielded a market boom of new, specialized test and measurement (T&M) equipment.
In the past, millimeter-wave test systems relied on software-leveling techniques that were unstable and at times damaged devices. In today’s market, mmWave T&M has real-time leveling techniques that offer power level control and power sweep control to protect sensitive devices. This provides test engineers with optimal power accuracy and stability during testing phases.
In the past, we've discussed how a new era of upgraded T&M equipment is helping designers vault 5G challenges. However, the discussion on burgeoning T&M equipment for mmWave applications has many dimensions beyond 5G that warrant discussion—include the testing challenges of mmWave technology and stand-out features of new products today.
Common Challenges of mmWave Testing
One of the challenges of mmWave testing high-frequency electronics is that, when transmitting data, these devices often suffer high propagation losses and inconsistent measurements. This means test equipment will often require higher power or better sensitivity to take accurate measurements, according to Anritsu.
Illustration of propagation loss vs. frequency. Image used courtesy of Anritsu
At mmWave frequencies, it can become a problem to use a spectrum analyzer and long cables to measure the path loss of a wireless link. Variable temperatures only make the issue of loss even more tenuous.
Clean and Tighten Connectors
There are a few simple ways test engineers are combatting these mmWave challenges.
First and foremost, Keysight Technologies suggests delicate male connectors or short custom connectors for the front panel of the test equipment.
Engineers must also upkeep connector interfaces, which are roughly 1/2 mm, and can easily accumulate dust particles and scratches. At mmWave frequencies, engineers may need a microscope to detect and clean these imperfections, which can damage the impedance match. Strong millimeter-wave connections also require strong connector torque, so users should also be familiar with a proper torque wrench.
Try to avoid over-straining or wrench-lift stress with the above techniques. Image used courtesy of Keysight Technologies
Another option is to reduce the number of connections in a test system altogether, directly cutting the number of points of failure and measurement errors.
Create a Remote Test Head
Portable spectrum analyzers and external mixers can be directly connected to an antenna, which allows the user to create a remote test head and measure as close to the device under test as possible.
For millimeter testing, direct connection to a DUT can yield more accurate measurements than a cable connection. Image used courtesy of Anritsu
Note that although these devices don't have the intermediate frequency bandwidth of a signal analyzer with direct and continuous coverage, a lower-frequency signal analyzer can easily cover these frequencies.
mmWave Test Equipment: SAs, VNAs, and VSGs
In addition to standard spectrum analyzers, vector network analyzers, and recently, even vector signal generators can be used for millimeter-wave testing.
Vector network analyzers (VNAs) are instruments that measure the network parameters of electronic devices. In order to choose the appropriate VNA, engineers should assess the design specifications of their project, especially those requiring accurate power control, wide power sweeps, and optimum noise range.
Keysight claims that a VNA is only effective and accurate when it is equipped with strong calibration capabilities. A crucial VNA function is the vector-error-correction, a mathematical technique that searches for systematic errors while monitoring output power and receiver noise.
While vector signal generators (VSGs) are not typically equipped for mmWave testing, the first VSG with mmWave testing capabilities became available in late 2020 and early this year. Rohde & Schwarz introduced a new vector signal generator, the R&S SMM100A, which is said to handle mmWave testing capabilities.
R&S says the SMM100A VSG is a real-time signal generation that operates through mmWave frequencies of 44 GHz. Image used courtesy of Rohde & Schwarz
Rohde & Schwarz says the VSG can generate up to 44 GHz while reaching nearly 7 GHz for Wi-Fi 6E networks.
A Growing Market of mmWave T&M
mmWave technology dates back to the early 1900s, and as such, there are plenty of models of mmWave T&M equipment on the market. Even the latest technology can overlook potential errors that surface during testing systems due to the wavelengths being smaller than standard microwave frequencies.
As such, it's important for test engineers to be aware of the many techniques—like proper calibration, connector maintenance, and portable instrumentation—to remedy the challenges associated with mmWave technology.
As long as T&M equipment operates through frequencies ranging higher than 50 GHz, test engineers have many options to choose from.
What other tips do you have for testing mmWave technology? Share your ideas in the comments below.