cst waveguide port

I only started to design antennas in a week.. sorry for the very basic question.
I′m designing a commercial patch antenna (just to learn using cst), using an discrete port, cst gives the the dbi value that the antenna specifies...but s-db, polar, VSWR is not working very well.. so i started to use "waveguide port", but i have this error:
"Waveguide for port number 1 is too short. The waveguide must be homogeneous for at least three mesh planes along propagation direction."
-i′m using template "Antenna with ground plane"
-the distance between the top of the reflector and top of PCB, is 6mm..
How can i build a correct waveguide port?

after many hours studying the tutorial and getting started and saw many CST examples...i managed to simulate the waveguide port.
My question now is:
1-what is the best template for patch 2.4ghz antennas with reflector distanced more than 6mm from the PCB?
2-to use the waveguide port in patch antennas, the coaxial feed start in the back of the reflector and end in the PCB (according to the tutorial), but when using an reflector exemple, is distanced 6mm from the PCB, the coaxial start at the reflector, but where it end′s the coaxial and feed? in the PCB?
3-using template "Antenna (on Planar Substrate)", if i do according to the tutorial, simluation take only a few minutes...but if i put the reflector -3mm in x position, and put some vacuum between PCB and reflector, the farfield simulation takes more than an hour...is there a way to reduce the time? or maybe Edit the farfield simluation to less parameters?
Sorry to ask, but the CST tutorials/help/getting started, are a little bit generalized.
thanks

How did you counter the error of 'waveguide port too short'?