Relation Between Fillet and Return Loss and Bandwidth.

Hello,


I have an UWB antenna that is composed of double sided substrate. I noticed that when i round the lower vertices of the upper side (patch) or the upper vertices of the lower side (ground) the matching improves, i reviewed the imaginary and real part of the input impedance and i found that they do get improve as the rounding increases. I am trying to find out how is this happening or an explanation to this but i cannot. Can any one help?

Thank you
Kawther