Are AC Analysis Results Reliable for High Frequencies?

I'm designing a distributed amplifier circuit in the Ka band, and I'm wondering whether AC analysis yields reliable results for this frequency or not? I'm observing my results using PAC, SP and AC analysis, the answer AC gives is consistent with my design calculations, but both SP and PAC give seemingly wrong answers. According to advice from my partner, it has to be the opposite, and it sounds like I'm getting something wrong. I know the difference between PAC and AC analysis, but why is only my AC analysis giving me predictable results?
P.S: I'm talking about Cadence Spectre.