(MIXER CIrcuits) Two stage MIXING simulation problems?????

Hallo,

I am currently designing a Rx on both Cadence Virtuoso and Agilent ADS, where I have two cascaded mixing stages. Usually, for a mixer CG simulation, I use PSS in parallel with PAC simulations to calculate the conversion gain and it works.

Now I have an insisting simulation problem, where the simulator (Cadence or ADS) calculate the correct mixing products for the first mixing stage, while for the second stage, it miscalculates it (frequency band and gain value) for the second stage mixing.

I suggest the problem is due to that the simulator only know the LO frequency (PSS) and the RF frequency range (PAC), I specified in the simulator. therefore, it can't calculate the correct results for the second stage using the output mixing products of the first stage as the input frequency range for the second stage!.

Please let me know if you can help me with this problem, please note that even TECHNICAL SUPPORT of one of the simulators I specified FAILED to solve this.

Thanks in advance!!!.