stripline port definition CST

Hello, in my multisection coupler structure i have a port shown as bellow(strip-line port) i have selected all three faces of the port and pressed ,"waveguide port" and i got the following window, what to do now , how to define in so i will get it functioning as a stripline port?
or do i need to define it as a desrete port, then how do you suggest to do that?
i am not sure regarding this final step
Thanks

Hello fiwi, what K should i take?
Thanks

k comes automatically after selecting surfaces and this...