Coupling LNA with passive mixer.

Hello,I have designed a simple sinlge-output LNA and I would like to connect to a current-driven single-balanced passive mixer.

Considering the I path only what defines the value of the coupling capacitance?Is there a formula ?

I would like to add that the mixer is 50% duty cycle.

Thank you in advance!

The best way to couple such devices is to match their inputs an outputs to e.g. 50 Ohms. Then you can test each and make sure the coupling is good.
Any coupling capacitance should have its reactance smaller than 1/10 of 50 Ohms at operating frequency.