Telstar Electronics wrote:
Go to the S21 function. Your S21 power is read in dB... remember to
always use the appropriate attenuators as those VNAs are very expensive
and usually have a lower input power maximum of a watt or two.

The statements above are generalities... you should refer to the
operation manual for the exact VNA you will be using.

www.telstar-electronics.com

One thing I forgot to mention... make sure you have a termination
(dummy load) on the output port. This load is generally quite small no
matter how much power you're measuring... in the several-watt range.
This is because of all the attenuation on the input port as I stated
before.

www.telstar-electronics.com