I found a design flaw in an RF front end I built. There is too much LO leakage into the RF signal on upconversion. I am using a standard mixer with high LO-RF isolation (~40dB) but the RF signals can be very low power (-90dBm) and the LO leakage can cause significant interference. The LO is at 2.396GHz and the RF signals range from 2.401GHz to 2.486GHz (The IF signal ranges from 5-90MHz). I am not using a quadrature mixer.

I'm looking for an inexpensive solution to reduce the LO leakage by about 40dB without redesigning the RF front end.

One solution I thought of is to add an IF mixer before the RF front to upconvert the original IF signal to a higher frequency before the RF mixer. The RF LO will now be at a lower frequency and will cause less interference, but leakage from the IF LO will still cause a spike at 2.396GHz.

Another solution may be a sharp notch filter on the RF output. I did some searching but I didn't find an RF filter that will remove the leakage and preserve the signal.

Any Advice?
Thanks

*Just a note about my application. This is an RF front end for a wireless channel simulator similar to the Propsim C8. The upconverted RF power level is so low because we are simulating signals going through the wireless channel. The output of the RF front end connects directly to the antenna port of a radio.

Yes, we are trying to mimic the power levels over the air, but we also have a number of signals from different radios we are combining together before upconversion, each with a different attenuation. Basically we have a real-time channel simulator for a wireless network. Adding a variable attenuator would work to reduce the LO component, but it would be too complex to add to the rest of the channel modeling system.

Thanks