January 15, 2019
There has been some discussion on how to effectively (from a cost, space, and time perspective) conduct measurements on passive components. Among the instruments engineers have in their test toolbox for this application include vector network analyzers (VNAs), along with oscilloscopes and waveform generators.
When selecting the proper VNA, it is important not to rely solely on third-party recommendations but to drill deeper and determine the best solution for your particular needs. This is especially true when it comes to compact USB VNAs and how to choose the right one to test cables, connectors, and antennas.
The aforementioned passive RF components generally do not require high levels of power control and “key” measurement performance associated with many VNAs, including certain USB models. Conversely, Anritsu has developed its ShockLine™ USB VNA family (figure 1) specifically for these applications. They are robust instruments with improved electrostatic discharge (ESD) and high maximum input levels that conduct s-parameter measurements at attractive price points to meet production test requirements.
Let’s take a closer look at what really matters when selecting a VNA for passive RF component verification during manufacturing.
Measurement Speed
Of course, throughput is essential during production. The specification on the data sheet, however, is only one factor in the equation that leads to the correct answer for, “How long does it take to make a measurement?”
When verifying passive device performance, the common practice is for the engineer or test technician to manually interface the VNA to the device under test (DUT). Therefore, throughput for these test setups will normally be dominated by the time it takes to connect and disconnect the DUT rather than the measurement speed of the VNA. As a result, selecting an instrument that simplifies test setup will save time and optimize throughput.
High Frequency Measurements
5G is one of the most ballyhooed rollouts in some time for the wireless world. New 5G requirements are driving the need to measure millimeter wave (mmWave) frequencies. Thankfully, the ShockLine USB VNAs provide wideband frequency coverage from 1 MHz to 43.5 GHz, well beyond the 26.5 GHz limit of other USB VNAs. This broader frequency advantage enables engineers to address the new 28 GHz and 39 GHz 5G frequency bands.
Having frequency coverage is only beneficial if the engineers have confidence in those measurements. The Anritsu ShockLine has best-in-class dynamic range above 20 GHz of 100 dB @ 10 Hz IF Bandwidth (IFBW) and better noise performance (6 mdB; 1 mdB typically) at 20 GHz than other comparable VNA solutions. Figure 2, showing the display of measurements taken of a 39 GHz duplexer, illustrates this advantage.
Configuration
How the analyzer fits into the production line is another key factor. As previously mentioned, having an instrument design that allows for easy access port connections will help lower measurement setup times. Ports on the front of the VNA enable engineers to more quickly and effectively tighten the port connectors for better measurement results.
Another factor is the space between the connector ports. On a compact USB VNA space is limited but spacing the ports a little more than three inches apart makes it easier to tighten the connections.
Recognizing the harsh environments associated with the production line, Anritsu also designed the ShockLine VNA family for use with ruggedized K connectors, rather than standard unruggedized 3.5 mm alternatives that are not as durable and can adversely affect reliability and measurement results.
To further withstand the rigors of the production floor, the VNA needs well-protected measurement ports. Strong electrostatic discharge (ESD) performance and high maximum input levels are key specifications to examine. For example, the ShockLine MS46122B has maximum port input levels of +23 dBm, +/-50 VDC and ESD performance of > 3 kV, for enhanced reliability.
The ShockLine VNAs are designed with a 1U chassis that is comparable in size to other USB VNAs. However, the ShockLine VNAs are the only USB VNAs to support up to 43.5 GHz frequency coverage compared to only 26.5 GHz by similar sized USB analyzers.
Cost-of-test
Similar to measurement speed, there is more to overall test cost than the list price. While there may be slightly less expensive USB VNAs on the market, their frequency coverage is dramatically lacking. For example, the ShockLine MS46122B VNA has frequency coverage up to 43.5 GHz, compared to only 26.5 GHz for competitive models. Despite the wide disparity in frequency coverage, the list price difference is less than $4,000.
Software can also have a large impact on the real cost of test. For example, the MS46122B uses the same control software as the remaining members of the ShockLine family. This enables easier transitions between USB and higher performance ShockLine VNA models as applications get more complex and test requirements grow. Other USB VNAs also share software but with very high-end instruments, making the transition from the USB VNA to a benchtop analyzer a much more expensive venture.
As we have outlined here, selecting a USB VNA for a passive RF component production environment is not as simple as reviewing a few banner specs that can be placed on a data sheet. All elements of the application need to be considered, so that the VNA purchased can fit into the application – both in the physical space on the production bench and its ability to conduct the measurements at the proper frequency.
To learn more about the ShockLine family and how it addresses passive RF component production testing, visit our compact USB VNA page.
