Signal modulation

[thundrous]

I need to have a constant 4 MHz AC signal (coming from a function generator) while sweeping the frequency (from the vector network analyzer (VNA) 9 kHz to 9 GHz) to read the scattering parameters.

I found RF mixers but unfortunately, they cannot handle very low (4MHz) and very high (9GHz) frequencies together.
Does DC-Bias works?

I am wondering what is the best way of doing this.

Suggestions are highly appreciated.

 

[FvM]

Are you asking about mixing (multiplicative), producing f1+f2 and f1-f2 signals or summing? In the latter case, a resistive 6dB coupler ("power divider") can do.