design of printed monopole antenna
Hi angolaX,
You structure is quite alright, however, you have defined wrong boundary. Just change all boundary to open (add space), everything would be fine. Moreover, it is better to define your waveport from the bottom of the ground plane (so, for rectangular monopole, it should start from z=-1 and for circular z=-2).
I've attached the return loss for both and radiation pattern of rectangular monopole at 3 GHz.
regards,
shameem