problem with subharmonic mixer simulation in ADS

Hi,
I want to design a subharmonic mixer in ADS. When I swept RFfreq VS conversionloss, the converionloss around the frequency (RFfreq=2*LOfreq) decreased drastically(the curve likes a ditch). If I change the LO frequency, the ditch on the curve of conversion loss also changes. It seems that DC power does not go to the IF port. And I am puzzled.
Can anyone explain it?
Thanks in advance.

Why should the DC power go to the IF port?

I think that IF band is from DC to several GHz, when RFfreq=2*LOfreq, the output of mixer should be DC. Does anyone meet this promblem when simulating subharmonic mixer?

---------- Post added at 05:49 ---------- Previous post was at 05:48 ----------

thank u, vfone
I think that IF band is from DC to several GHz, when RFfreq=2*LOfreq, the output of mixer should be DC. Do u meet this promblem when simulating subharmonic mixer?