Downconverter design RF = LO

Hello All,

We are putting together a home-made 1-port VNA in the low GHz <6 GHz. I attached a super simple block diagram of what we plan on creating. I was wondering if is still possible to retrieve the phase information of the downconverted IF if the LO and RF are the same frequency? Perhaps looking at the second harmonic? Although n*(0) should still be zero...

Let me know your thoughts, and thanks for the help
Sami

I think if the LO and RF are the same, the IF output is DC, so you need them to be slightly different.

The structure you show is essentially a vector multiplier, so if the LO level is high enough to saturate the mixer, the IF output voltage will correspond to LO/RF phase. A phase shifter is needed to calibrate the multiplier.
Another name is correlator, or lock-in multiplier.



Also, a synchronous detector is another name

A VNA needs quadrature mixing, a zero IF receiver needs it anyway.

I agree. Some research for "zero IF receiver" alias "direct conversion receiver" will help to understand the required topology.