Radiation pattern of Cirular and square monopole

Hi
In many papers its cited that the radiation pattern of square monopole is better than the radiation pattern of circular monopole but unfortuately non of the paper describes why? Is there some specific reason that the pattern of the square monopole is better or is just an observation from measured results.

1) How to analyze the pattern from geometry
2) Is there relation between surface current distribution (or any other characteristics) and radiation pattern.


Thanks