I have designed a LNA block with high gain and low noise figure and now i want to co-simulate it with an ideal mixer (HB simulation in ADS). LO frequency initially is higher than RF frequency. The result show that chain NF is much higher than expectation from friis Equations at the end of the frequency band. when i change LO frequency to a value that is less than RF frequency, the NF is fixed and i cant find any reason for the problem. appreciate any help that anyone could offer. note that image frequency is completely rejected.