How to give complex impedane(12-151 j) in CST Microwave studio 2011?

I am designing a bow-tie RFID tag antenna.I want to use chip (IC). As the impedance of chip is in complex form i.e 12-151j but when i use this impedance while assigning ports. it gives error.It works only on real values i.e 50 ohm, 70 ohm etc. how to give complex impedance in CST?

As far as I know you can't set a complex impedance in CST.
Set the port to 50Ohm, read the impedance (for example from the smith chart) and do the math by yourself.