size of waveport for antipodal vivaldi antenna feed

hi all,
can somebody tell me how large tha wave port of antipodal vivaldi antenna might be?
if the width of the antenna is 25 mm for 5 GHz frequency,can i give it a waveport of 22 or 24 mm width?

It might be a good idea for you to do a convergence test on this for yourself. Start by making the waveport something like 2X the gap on each side and above/below the conductors, and simulate the fields in the port. If you still have signficant field strength getting near the sides of your port, then expand it. Keep enlarging the port until your results for the Zo for the port settle, or until your simulation results settle. The key is capturing the significant fields to the point where the error due to waveport size is low enough to not effect your results.