Mixer test setup specific questions

I have a 0.5μ mixer design, to be measured in an on-wafer station. For RF port I apply 900MHz, do not have 50Ω input matching.

- Is it neccesary an input network matching at this frequency for on-wafer testing purposes ?
- If yes, I was thinking on measure the input reflection coefficient and maybe in this way I'd know how much voltage is incident in the mixer's input. What do you suggest?
- If measure S11, does LO source have effect on this measurement ?