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calibration of VNA with 180 hybrid

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Advanced Member level 4
Oct 20, 2006
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+calibration kit +vna

I'm measuring S11 for my chip (differential topology) which required to use a hybrid 180 degree. How to calibrate the differential output? That is, how should I calibrate the VNA when the hybrid is connected?

Since I have just one SMA calibration kit, I used both of the male and female to calibrate. Match and Open are Ok, but Short gives some complains.

back to back calibration vna

Several comments

I have contemplated the difference between a balun and a 180 degree hybrid for a while and have come to the conclusion that while both have outputs that are 180 degrees apart there is another distinction. The balun is intended to convert from a single-ended to differential (or balanced) transmission line as well. The two devices are not completely interchangeable. You may be better served with baluns.

You may consider building a two part test fixture for your part that has a test coupon that mirrors the part test footprint but is connected back to back. You can then test the part and extrapolate the performance of the test part by de-embedding the measurement using the coupon measurement. Essentially you are looking at the difference between the two measurements with the VNA calibrated to the coax.

Buy a second calibration kit so you don't run short of standards.

VNA's exist with four ports and can make differential measurements directly.

Is it not better to calibrate only one leg and keep the other leg match to 50 ohms? I am not very familiar with VNA myself.

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