Transmission line at higher frequency with Rogers RO3003 substrate

Hi all,

I have designed a CPWG transmission line in EMPro using RO3003 substrate. I calculated the dimensions for 50 ohm transmission line at 60 GHz. But after simulation at 60 GHz its not showing 50 Ohm. At lower frequencies it is showing constant 50 ohm but at higher frequency it is changing abruptly. I have attached the result snapshot here. Could anyone suggest me why this is happening?
or this material (RO3003) is not valid at higher frequency ? but in data sheet it is written that it is valid till 77 GHz.
Any help would be appreciated.

Thank you.

I doubt that the R03003 material definition can cause the impedance changes. So everything is about your simulation geometry, meshing and other settings, but nothing that has to do with RO3003 substrate.

Your attachment doesn't give much information, but there could be higher order modes present in your simulation -- which have different impedances.