hello
1-first draw one circular plate in (0,0,0) point by λ radius.
2-draw 1 cylender that its radius is 5mm*exp(5/6) and center is ( 0,0,-5mm) and height is 5mm and its material is vaccume.
3-draw another cylender that its radius is 5mm and center is ( 0,0,-5mm) and height is 5mm+λ/4.
4-substract circular plate and first cylender.
5-select circular plate and by right clicking set it perfectE boundary condition.
6-select external surface of second cylender and right clicking set it perfectE boundary condition.
7-draw one circular plate in (0,0,-5mm) point by 5mm*exp(5/6) λ radius. and select it and set it to wave port by right clicking ....
8- draw one cilender for redaiation box.
9-set analyzing and run it.
by my freind