drawing coaxial feed for antenna

Hi
I read a paper in which exact structure of a fat dipole microstrip antenna is described.
My question is about the feeding structure. Is it necessary to set up for example a coaxial feed and its entrance as input port or we can draw port right at the antenna?
Is there any difference between ADS, CST, HFSS in this regard?

Antenna simulation with defined port gives almost same result as port defined at the coaxial input. But defenelty port defined at coaxial input will be more close to real world design.