Problem in CST waveguide port

Hi,
While simulating antenna structures in CST using wave guide port there is a error message "Wave guide port 1 is too short, it must be homogeneous for at least 3 mesh cells" how to improve the mesh cells to resolve this problem.....

I tried to create curve equation using macros for vivaldi antenna .but it is not working i am using spline option to create the curve.some body give solution for this issues.............

Yes, Actually the physical structure of what you have connected to your wave port should be "homogeneous for at least 3 mesh cells". This is becasue you use a spline profile to create a port and the distance between two sides of your slot is changing continuously. I suggest connecting another peace of slot with a constant gap size to you tapered slot and then connect that to your wave port or to define such a tapering in you spline that gives you constant gap size at the end at least for 3 mesh. Is it clear?