The Definition of 2LO to RF Isolation

Hello, there,

I have a question that within the subharmonic mixer, what is the definition of 2LO to RF isolation? I see the LO to RF isolation is calibrated by LO@RF/LO@LO. What about 2LO?

Thanks a lot.

Hi,
A subharmonic mixer will use the first harmonic (in most cases) of the LO signal you input in the mixer to mix with your IF.
Let take an example:
We use a subharmonic mixer, we come with a 10 Ghz LO signal in and a 1 GHz IF. The mixer will internally mix the 2*10 GHz with the 1 GHz IF.
Mixer used as an upconverter, the 2*LO to RF isolation will be the isolation between the 20 GHz LO signal (2*10) and the 21 Ghz RF signal.

Hi jiboune

Thank you for your reply.

I wonder where to measure the 2LO signal power? Because there may be some other stuff like buffers following the mixer core. Do you mean I pick up the 2LO power at the output port, which is also one of the output spurs, right?

In the case you gave, the 2LO to IF isolation would be the power of 2LO at IF port divide the input IF power?

right, you measure the 2*LO level at RF output.
For 2*LO to IF isolation you measure the 2*LO leakage at IF port with a directional coupler.

If so, the isolation should be high enough no matter what situation it is used in? I simply design a subharmonic mixer but find the power of 2LO at the input is very close to the input signal power. Is there any mixer working with poor iso in the real world?

Harmonics from a non linear device. These must be attenuated as much as possible .