Along with the materials used for 6G, the other key aspect of 6G is component characterization. Because 6G devices operate at extremely high frequencies, characterizing them is crucial to understanding their performance at these higher frequencies. The tiny size of these devices demands specialized skills for characterization and configuration, such as a vector network analyzer (VNA), a test station, probes (with very small steps on the order of 100 µm or 75 µm) with a high-resolution camera, and a skilled professional capable of performing tests on the device at water level and experienced in taking measurements to assess the accuracy of calibrations. Device characterization is especially important for device modelers, as they need to verify the bandwidth response and harmonic content of their 6G devices. To perform broadband measurements, they require a broadband sweep VNA.
2. What performance characteristics are important and what values do they need to achieve?
Navneet: From a materials and measurement perspective, the main performance characteristics that need to be measured and validated are material properties such as dielectric constants, effective permittivity, loss tangents, conductivity, and so on. The parameters are the same as with any material, but the measurement techniques for these parameters are and will become increasingly complex with 6G materials. Given that the materials will be so thin and are expected to operate at extremely high frequencies, great care must be taken when selecting the measurement method and when performing the measurements.
Several research studies suggest various methods for taking measurements on materials, all with their advantages and disadvantages.
Regarding device characterization, the most important feature is the measurement of the S-parameter, which indicates the device's performance. The S-parameter, or scattering parameter, indicates the proportion of the signal reflected by the device (S11) and the efficiency of the signal as it passes through the device (S21). Measuring the S-parameter at such high frequencies (on the order of 140 to 240 GHz) presents its own challenges due to the size and behavior of the device. To date, Anritsu has tested various active and passive components with the highest levels of precision and accuracy.
3. What challenges do developers face when testing these components and materials?
Navneet: Material measurements are always very complicated but also very interesting. Developers are always asking themselves:
• What measurement method is most suitable for your materials? Resonant or non-resonant methods? What clearance?
· What is more important, the accuracy of the measurement or a bandwidth measurement in itself?
· Which measurement method will provide the fastest and most accurate results?
· What accessories can support such a thin material, sheet, or substrate?
• What type of environment is needed to test the material?
· After taking the measurements, how do you confirm that they are correct?
All these questions plague developers and create uncertainty. Choosing the right measurement technique is the most important issue to address and the one that requires the most time. Other important factors include the repeatability of the measurement across the entire system.
Regarding device characterization, developers, and especially those developing device models, are very interested in the harmonic content (3rd and 5th harmonics) of the device under test. Therefore, broadband sweep measurements (covering frequencies from low to extremely high frequencies, e.g., 70 kHz to 220 GHz) for S-parameters are always preferable. This allows for the easy identification of problematic areas in their devices and ensures that design changes or other preventative measures are implemented. As noted in the initial question, the main challenges when taking these measurements on high-frequency devices are ensuring the repeatability, stability of the measurements over time and temperature, and guaranteeing their accuracy.
4. How do these difficulties differ from those of 5G?
Navneet: The challenges posed by 6G measurements are a little different and somewhat more complex in nature than in 5G.
For 5G, since the frequencies are lower (28/39 GHz) than with 6G, manufacturing, measurements, and testing are relatively simpler. Although the basic questions are the same, both for material measurements and device characterization, the process of performing these measurements is relatively complex in 6G, as is evident from the answers to the previous questions.
The difficulties also depend on what measurements the user is trying to perform; for example, a user trying to characterize a broadband power amplifier would need to introduce extremely low power levels into the amplifier, around -50 dBm, etc., which would not be easy in an extremely high frequency range. However, a customer characterizing a waveguide component at 140 GHz might require more power.
5. What role does vector network analysis play in these measures?
Navneet: The vector network analyzer (VNA) plays a crucial role in performing all the measurements mentioned so far, whether in 5G or 6G. The basic functionality of a VNA is to input a signal into a device and observe the signal at the device's output after passing through it. A VNA relies on a tuned receiver whose receiving port knows what the transmitting port is transmitting, specifically the frequencies and power. The VNA's role is even more important in the 6G era as devices continue to increase their frequencies and decrease in size. Inputting a very accurate and precise signal into the device, and then monitoring/detecting the output signal, which can have extremely low power, is the most important characteristic of a VNA. A VNA is capable of scanning both very low and extremely high frequency signals, meaning that 6G devices can be characterized across a very wide frequency range. The Anritsu VectorStar is the only VNA in the world capable of scanning between 70 kHz and 220 GHz in a single sweep. Other applications require testing 6G devices only in a specific band, which is the band of interest to the user. VNAs can be combined with external millimeter-wave multipliers to perform measurements only in these frequency bands. Whether for single-band or broadband applications, the VNA plays a crucial role in all device characterization and modeling measurements.
The same applies to high-frequency material measurements. Even for material measurements, the primary element responsible for controlling and calculating effective permittivity, loss tangents, conductivity, etc., remains a VNA (Vector Network Analyzer). All these parameters are calculated from the reference S-parameter measurements performed by the vector network analyzer. Furthermore, for material measurements, depending on the application and user expectations, the measurement can be for a single band (in most cases) or broadband. In addition to the VNA, the user needs an appropriate accessory for material measurements, into which the material is placed before taking the measurements.
Since most of these 6G active/passive components and devices are on a wafer and operate at very high frequencies, a VNA together with a test station (manual or automatic) and probes with the appropriate pitch constitute a complete solution for measuring any 6G component/device.
Therefore, the VNA is the basic functional building block for any 5G/6G measure, whether in the design, packaging, or final product phase. Each phase requires thorough testing and reconfirmation that the device is functioning correctly. The VNA guarantees this performance.
6. What solutions does Anritsu offer for 6G measurement and analysis applications?
Navneet: Anritsu offers several solutions for 6G. One of the most important is the vector network analysis solution, which explores the broadband frequency range from a minimum of 70 kHz to a maximum of 110/125/145/220 GHz in a single sweep. This has proven to be a major advantage for customers characterizing and developing device models. Until recently, measurements were taken in a specific band (e.g., 90 to 110 GHz, 110 GHz to 140 GHz, and 140 GHz to 220 GHz) and then in other bands to see how their devices responded across a wider frequency range. There were many inconsistencies when taking measurements in a single band, and many difficulties arose when purchasing multiple modules, waveguides, probe interfaces, and millimeter-wave probes for a single band. These were necessary to completely change the configuration from one band to another, and they added to the difficulties in achieving repeatability, installation, and stability of the entire system, all of which constituted a huge obstacle. Anritsu's broadband solutions provided broadband frequency coverage between 70 kHz and 145/220 GHz, resulting in significant savings in time, energy, and money.
No other test and measurement company can offer anything like this. Anritsu's VectorStar is also compatible with almost all third-party solutions for material measurement. This collaboration has been very helpful for customers, as it gives them a range of options. Customers can choose from specialized solution providers based on their material requirements, and Anritsu's VectorStar is already compatible with them.
The Anritsu VectorStar is not limited to characterizing materials and devices; it is also compatible with almost all antenna measurement solutions. Thanks to its superior performance and upgradeability (number of ports/sources/support for broadband millimeter waves), the VectorStar is the preferred choice among our customers for measuring 6G antennas. Measurements include, among others, active and passive 6G antennas, AiP (Antenna in Package), and more—all feasible with the Anritsu VectorStar.
7. What features make it particularly suitable for 6G R&D?
Navneet: Anritsu's VectorStar-based broadband solutions are particularly well-suited for device characterization, device modeling, material measurements, and antenna measurements, among many other applications. These are some of the features that make Anritsu's VectorStar-based solution appropriate for 6G measurements:
• Superior dynamic range across the entire frequency range
• The very small size of our millimeter modules, based on the most advanced nonlinear transmission line (NLTL) technology, provides a direct connection to probes and devices without the need for long, expensive cables that are subject to extremely high losses and measurement errors
• Extremely stable and accurate automatic control (ALC) when connecting to millimeter wave modules
• Extremely good levels of stability and repeatability in measurements with respect to time and temperature thanks to the patented NLTL technology we use in our millimeter wave modules
• Powerful and sophisticated calibration algorithms for high-frequency measurements that guarantee best-in-class calibration and residual specifications
• Advanced de-embedding techniques and software algorithms compatible with various types of UFX (Universal Fixture Extraction) extraction systems
· For characterization of active devices (such as amplifiers), it is possible to handle very low input powers with VectorStar ~-55 dBm/- 60dBm.
• Compatibility with third-party solutions for material/antenna measurements, test stations, and millimeter wave multipliers, among many others.
Navneet Kataria is Product Manager at Anritsu Corporation
