By utilizing the R&S ZVA-Z110 inverter module, Rohde & Schwarz's high-end vector network analyzer can extend its frequency coverage up to the 75–110 GHz millimeter wave band (W-band). This module is designed for ease of use, helping customers save both time and cost from the very start of their design process. Importantly, using a proper four-port network analyzer with a pair of inverter modules eliminates the need for additional hardware circuits. In recent years, multi-port measurements have become increasingly important, and this article presents a solution that is the first to implement full multi-port and balanced measurements in the W-band.
What is inside the inverter module?
Figure 1 shows the CAD structure and block diagram of the R&S ZVA-Z110. The inverter module includes components such as channel source frequency multipliers, adjustable waveguide attenuators, directional couplers for isolation reference and measurement signals, and a wave mixer for down conversion.
Figure 1: Transparent CAD structure and block diagram of the R&S ZVA-Z110 (adapter without test port)
S-parameter measurement of the filter
Let’s take a mixer and set up a 90 GHz bandpass filter as an example to walk through the testing steps.
Step 1: Configuration and setup
In areas A, B, and C shown in Figure 2, the following configurations are made: select the inverter module model in area A, choose the cable connection method in area B, click the application button in area C, and connect the inverter module to the network analyzer (see Figure 3). Then adjust the frequency axis to 75 GHz to 110 GHz (see the bottom of Figure 2). Additionally, all settings for the inverter module are automatically configured, including RF and LO multipliers, optimal power levels, reset settings, connection type WR10, and definition and selection of the waveguide calibration kit R&S ZV-WR10.
Figure 2: Settings dialog
Step 2: Calibration
This example uses TOSM calibration technology along with the R&S ZV-WR10 Waveguide Calibration Kit (see Figure 3). The R&S ZV-WR10 also supports other calibration methods such as TRL, UOSM, TOM, TRM, and OSM. It includes sliding match functionality, which increases directionality and load matching to 42 dB and 40 dB, respectively. Due to the radiation effect when a waveguide is open, the open circuit in the calibration component is replaced by an offset short circuit, composed of a spacer and a crowbar at a λ/4 offset from the center frequency.
Step 3: Measurement
Figure 3 shows how a mixer, R&S ZVA24 vector network analyzer, and two R&S ZVA-Z110 inverter modules are used to measure a 90 GHz bandpass filter. The filter has high rejection characteristics and a wide dynamic range. The R&S ZVA-Z110 inverter module sets a new standard for dynamic range, with a typical value of 110 dB, easily meeting the high dynamic requirements of filter measurements. Users can increase the measurement bandwidth, such as setting it to 1 kHz for faster measurements.
Figure 3: Full millimeter wave measurement setup with a 90 GHz bandpass filter and R&S ZV-WR10 waveguide calibration kit
Beyond filter testing, the Z110 is suitable for a variety of other applications. For instance, due to its built-in W-band attenuator, it can provide very low excitation levels, making it ideal for testing low-noise amplifiers without any issues. It is also well-suited for compact designs and production lines that require fast scanning, such as on a wafer probe station. Passive cooling without a fan is another advantage. Additionally, it is ideal for multiport and balanced port measurements in the millimeter wave band.
Multiport measurement
Until now, multiport and balanced port measurements were limited to around 50 GHz due to mixer constraints. However, many applications in the W-band involve balanced or multiport devices—such as in ranging radar, defense, and aerospace systems. With the R&S ZVA-Z110 inverter module and the R&S ZVT20 vector network analyzer, up to six measurement ports can be supported.
Three-port measurement of directional coupler
1. Why use three-port measurement?
Using three inverter modules and a suitable vector network analyzer, a three-port coupler measurement can be completed in a single connection (Figure 4). This significantly reduces measurement time and allows simultaneous measurement of all 3×3 S-parameters without multiple connections or repeated 2-port calibrations. Instead, a full 3-port calibration is used, offering more accurate results.
Figure 4: Three-port measurement requires only three inverter modules
2. Measurement setup
The R&S ZVT20 can support up to four inverter modules without the need for an external signal source. This compact solution requires no additional hardware and provides high measurement speed. In the three-port application mentioned earlier, only three of the measuring ports (ports 5 and 6) of the R&S ZVT20 inverter module provide the local oscillator signal. If needed, an external Wilkinson splitter can be used to distribute the local oscillator signal to all inverter modules.
UOSM calibration
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