How does Vector Network Analyzer (VNA) measures S parameters in reality?
Namely we have equations:
In theory, if i wanted to calculate scattering parameters I would have to be able to make perfect matching on the source (\$a_1=0\$) and on the load side (\$a_2=0\$).
Unfortunately I do not understand how is this done inside the VNA. If I want to measure scattering parameters of a random network with input and output impedance different than 50ohm, how is in this case achieved \$a_1=0\$ and \$a_2=0\$?