power CPW mode in HFSS
How many modes are supported by the wave port that you have set up? View the fields on the ports to determine if you have set up the correct CPW mode. Remember that the wave port sidewalls must extend over and touch the side grounds to set up the correct mode.
I would think that if there is only one propagating mode on the port, then that is the accepted power of the CPW mode on the port. If there are multiple propagating modes, that's probably not a good thing. The S11 value will tell you how much of the the input power is reflected from the antenna.
I hope this helps -- I don't quite follow all of the question. Good luck.