cst ifa antenna feeding port help

Hi all,
first of all i would like to confess that i am a newbie in rf design and i may ask very silly questions. please forgive me and i am waiting for your responses.
I am trying to design a pifa and/or ifa antenna (all of them are PCB microstrip antennae) in cst design environment. when i was investigating reference example designs on internet
i saw that the are using waveguide ports in order to feed antennae.
So, my first question is which feeding port is most suitable for this type of design.Discrete port or waveguide port. If discrete port is prefereble then how can i use it and how can i increase its accuracy whne simulating S parameters and far field directivity of the antenna.
If waveguide port is more suitable then i have some more questions. Becasue in the internet i saw that size of waveguide port should be as large as possible and there are some rule of thumbs to achieve this criterion. Also there is a macro in CST called calculate port extension coefficent and when i use this it generates a relatively huge waveuide port.
The problem in my case is in my ifa design shorting arm of the ifa is very close to arm from where i excite antenna via a waveguide port.So, waveguide port overlap this two arms unintentionally.
When i performed some simulations with different sizes of waveguide port, i noticed that S11 and farfield results are totaly different from each other and i cannot comment on the results. By using a relatively small waveguide port that does not overlap inductive shorting arm, can i get reasonable results or how can i assure myself?
One more step to ramify my question is that i am trying tofeed my antenna inside the board not the edge of the board since in the real usage i will generate rf signals from PA that is located nearly in the middle of the board.
Sorry for the long explanation of my problem but as i said before i am a newbie and i need some explanative help.
Javier.

Ok let's try:
1) : It depends I think, if you have just your antenna, waveguide excitation would be correct if you use for example some microstrip or cpw as feed. In your case, I recommend a discrete port if you connect the pa directly (via bond wires and short traces) to your antenna. The discrete port has no accuracy, it's normally a current source with a fixed impedance. All other things are calculated.
2) : in the manual are rule of thumbs mentioned for waveguide ports.
3) : You can use some uniform feeding line (e.g. microstrip) and shift the reference plane -> manual
Hopefully it helps a little bit. But also read the manual, many of your questions are explained there.

Many thanks johnjoe i am gonna follow your insturctions and read manually carefully one more time and i am gonan share my experience here later.