Millimeter-wave measurements using the Agilent PNA-X network analyzer

Between 30 and 300 GHz, applications for mmWave measurements are increasing. From high data rates to the automotive industry to radio astronomy, flexible measurement solutions are increasingly showing their advantages. In these applications, mmWave measurement solutions must comply with many rules. For example, wafer device characterization in a probing environment, or module testing through waveguide or coaxial interfaces. Solutions also include material measurements in a fixture or in free space, or outdoor/indoor antenna testing.

Compared to sub-3 GHz applications, current requirements for mmWave components are relatively low, but the expected performance is very high. Therefore, measurement solutions with scalable frequency range and measurement capabilities will provide greater flexibility to accommodate a wide range of applications.

In many emerging electronic technologies, the initial components (e.g., devices fabricated on wafers) are the basic building blocks. These devices are then diced and joined to circuits via wire bonding, ultimately becoming highly integrated modules with increased functionality and packaged into a very small footprint. Devices are first characterized as wafers before further testing as modules. The data obtained when testing these wafer devices can be used for parameter extraction to build models, which can then be used for circuit simulation.

Making mmWave measurements

Building accurate circuit simulation models requires a high-quality, 220-GHz probing solution. For example, Figure 1 shows a 50-nm T-gated deformed GaAs HEMT wafer measurement from 140 to 220 GHz1. All four S-parameters can be viewed simultaneously. See trace S21 on the lower left, intersecting the X-axis at approximately 150 GHz. To reveal the true gain of the device, the .s2p file (raw data) needs to be de-embedded, either inside the network analyzer or offline.

The measurements were performed using an Agilent N5250A PNA Series millimeter-wave network analyzer with a 140 to 220 GHz (N5260AW05) test probe module, and on-wafer measurements were performed using a Summit Series 12K probe station from Cascade Microtech. (Figure 2 shows the 110-GHz version of the system.) All two-port on-wafer calibrations were performed using Cascade Microtech’s WinCal 2006 calibration software, with the order thru, reflect, reflect, match (LRRM).

By adding a modulator (Agilent Z5623AH81) and a dual output pulse generator (Agilent 81110A), the same device is transformed into a solution for pulse measurements. Figure 3 shows pulse profiling measurements of a simple thru device in the W-band 75 to 110 GHz. The pulse setup for these measurements is as follows:

RF pulse width (PW): 2μs (50% duty cycle); pulse width (PW) can be reduced to 20 ns

B Receiver Strobe Pulse Width: 20 ns (0.5% duty cycle)

Measurement frequency: 100 GHz

Pulse shape is a very useful analysis tool because it shows any pulse distortion caused by the device under test (DUT). It is done by stimulating the DUT with a pulse signal at the input and then folding the signal back at the output to determine the changes in the pulse shape. All of these changes indicate non-ideal (e.g., nonlinear) behavior of the device under test (DUT).

Modifying the system to cover different mmWave frequency bands is as easy as replacing a test probe module. For example, replacing the N5260AW05 (140 to 220 GHz) module with the N5260AW03 changes the frequency band from 220 to 325 GHz. By adding two external frequency synthesis sources (e.g., Agilent PSG signal generators), the dynamic range or trace noise of the system can be easily increased above 200 GHz. Each frequency synthesis source is configured with Option 520 to cover the 20 GHz frequency range; one provides the RF signal and the other provides the local oscillator (LO).

The same equipment setup can also be used to make related measurements such as average pulse, point within pulse, and pulse-to-pulse measurements. This configuration can also be used to make indoor antenna measurements, using pulsed mmWave techniques to filter out unwanted signals.

In addition to wafer, pulse and antenna applications, mmWave solutions are also widely used for material measurements. Figure 4 shows a W-Band 75 to 110 GHz system performing material measurements in free space. Due to the small size of the W-Band waveguide interface, free space technology provides a more manageable sampling volume (compared to the W-Band waveguide interface volume). With mmWave solutions, Agilent's unique gate-reflect-line (GRL) calibration technology can be utilized, which provides high accuracy without the need for additional hardware (which is usually expensive).

in conclusion

As shown in the previous examples, the PNA Series network analyzer mmWave solutions can be adapted to suit a wide variety of applications (Figure 5). This universal solution is the most effective way to address today’s broad range of applications and disciplines. It also reduces the need for multiple single-target measurement systems.

For future frequency band millimeter wave applications, the Agilent PNA-X network analyzer (N5242A) can also solve all the measurements mentioned here. To take full advantage of the analyzer's latest features and capabilities, simply replace the PNA (E836xB) with the N5242A in each of the solutions shown.