Problem Simulation C-PAtch Antenna with HFSS 9.1

I'm trying to simulate a c-p@tch antenna as described in the paper 'The C-P@tch: A Small Microstrip Element by G. Kossiavas, Electronics Letters, 1989, p253-254'. (Frequency: 413MHz)

I draw the antenna in HFSS (see file) but I suppose I do have a problem with my port. Can anybody help me out? My S11 is about -2dB

Thanks a lot