Need help in CST simulation

During the transient solver
The error show this "Some higher propagating modes at port 1 are not considered time domain calculation. This possibly leads to an inaccurate energy balance. Consider to reduce the port size or decrease upper frequency limit."
Any guide to solve this problem?

for removing this error first increase the port size i.e. increase the thickness of ground plane in which u assign port.
or u can also increase the mesh cell and then this problem also removed.

sure. thanks