Hello,

since the simulation is meant to reflect the reality the thickness depends on the material you will use when you finally manufacture your device. Check for instance Rogers Corps. who proposes microwave PCBs. They propose copper cladding ranging from 1/2 to 8 oz/ft² (equal to 8-70 µm) thick copper.

hello dear camilla

my substrate is rogress 5880. the thickness is 0.508 mm. when i search the data sheet i found the copper thickness 1 oz. 

Generally, PCB copper thickness unit is oz. & 1 oz = .035 mm. You can have 1/2 oz to about 6 oz

Based on perturbation theory, you can simulate your structure without any thickness. The parameters of structure is more relied on structure geometry to metal thickness. addition of thickness would have slight effect in frequency response of ur structure