Please tell me, is there a difference between testing a four-port device directly with a four-port VNA and testing a four-port device with a two-port VNA with the other two unexcited ports connected to matched loads?
When I tested the differential line, I used a two-port VNA because I didn't have a four-port VNA, but the reflection coefficient of the test result was much worse than the simulation result, going from below -15dB in the simulation to only staying below -10dB. In my simulation, however, I added the SMAs at exactly the same dimensions as in reality, and the simulation showed that the reflection coefficient would not be as bad as the test results.
Basically not since one can transform any 2 port vna into a 4 port one with anexternal rf relay matrix
Fritz Caspers Thanks a lot, some of the results I got from my measurement were similar to the simulation, so it shouldn't be a problem with the simulation, right? Wouldn't there be a lot of reasons for such errors that would be difficult to troubleshoot? For example, is it possible that I didn't do a good calibration because I wasn't familiar with the VNA I was using at the time?
Calibration in the manual mode is tricky on a 4 Port VNA.Better use an electronic cal kit.What type of NA did you use wnd which type if calibration?(manual or electronic cal kit).there are ways for verification to check that you calibration is ok..also which type of cables did you use?
Hello Hao ..I guess you used a SOLT calibration not a slot calibration.
Perhaps we can continue the discussion by normal e-mail ([email protected])
What is you device to be tested?
Yes, we can easily use a 4 ports VNA to measure a two ports devices. Just when you do the SOLT or other calibration method, you have to define your ports you should use to measure you 2 ports device in the calibration setup (Cal-all or basic_Cal).
Yes, there is a difference in accuracy between testing a four-port device with a four-port VNA and with a two-port VNA.
A four-port VNA can measure all four S-parameters of a four-port device directly, without any need for approximation or extrapolation. This provides the most accurate measurement of the device's performance.
A two-port VNA can only measure two S-parameters at a time. To measure all four S-parameters, the device must be connected to matched loads on the unused ports. This can introduce errors into the measurement, as the matched loads may not be perfect and the reflections from the unused ports may not be negligible.
In addition, the two-port renormalization technique, which can be used to calculate the missing S-parameters from the measured S-parameters, is not always accurate. The accuracy of the two-port renormalization technique depends on the accuracy of the measured S-parameters and the reflection coefficients of the matched loads.
As a result, the accuracy of testing a four-port device with a four-port VNA is generally better than the accuracy of testing a four-port device with a two-port VNA.
Here is a table summarizing the accuracy of the two methods:
If you need to measure the S-parameters of a four-port device with the highest possible accuracy, then you should use a four-port VNA. If you do not have a four-port VNA, then you can use a two-port VNA with matched loads, but be aware that the accuracy of the measurement will be less than ideal.
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