Folks,
Thanks for all the comments. I notice that the diagram provided by erik does not indicate any protection. Thanks for that diagram. The 50 ohm bridge mentioned above does provide some help but only a small amount. ESD events are often in the thousands of volts so even a few dB of attenuation is not enough. I have previously blown up a VNAs input switch when I touched an antenna connected to the VNA in my workshop so this is a real concern for me. Yes, it was repairable. I got to learn a lot about soldering very tiny surface mount components in that case.
Back-to-back zener diodes are available for this very purpose with very low capacitance (0.06 pf) for example the PGB010603 made by Littlefuse. I have attached a data sheet for others to consider. The spec sheet says it is good up to about 9 kv for a contact discharge and about 15 kv for an air discharge. Furthermore, the response time is under 1 ns which is about 1 cycle at 900 MHz. I suggest the mixer in the nanovna won't handle a typical ESD event without some help. I purchased some of these devices for about $0.50 each so they are not a big investment. Please be careful interpreting the data sheet. You might conclude these diodes don't help, but they have in my case.
I hope that when we do an open calibration any stray capacitance such as 0.06 pf is measured and removed. 0.06 pf at 900 MHz is a reactance of about 2950 ohms which should not have a major impact on most measurements anyway.
I hope folks find this information useful.
--
Bryan, WA5VAH
