S parameters in HFSS

I'm designing a switch in HFSS. I need some help understanding the results. The S parameters are for a switch in OFF state. I understand that S(1,1) nearly being 0 means that the switch is off and all power is reflected. What I'd like to understand is why is the curve shaped this way? and what does S(1,2) being equal to S(2,1) signify?

The S21 and S12 represent the power travelling from port 1 to port 2, and vice-versa. They are the same, since the device is reciprocal (the power sees the same effect travelling either way; the same with any passive device). The curve looks that way because the switch is not perfect -- there is some power leakage through the device, but not much (< 60 dB)!