Truncated plane wave in CST?

is there a way to send a truncated plane wave in MWS5.1? normally MWS sends the plane wave across the whole plane.

Generally the plane wave has infinite dimensions, or say the maximum available in time domain simulation; your proposition is quite unphysical..
What's the purpose of using finite plane wave?

actually, I wanted to send a tilted gaussian wave to a structure. The structure has a negative refraction over a frequency range.I want to demonstrate that the incoming wave is negatively refracted. Unfortunately, MWS does not have a gaussian wave (spatially). so, I tried the plane wave, but it has infinite dimensions. So it is useless for this purpose.