pifa vs traditional 1/2 wl mpa

when i think about the polarization and radiation mechanics of the trad 1/2 wavelength mpa i can clearly understand them.

however, when i try to apply this same logic to the pifa i cannot come to the same conclusions. why would there be pure polarization? and what is the radiation mechanic?

does anyone have a paper that describes this process or understand it clearly themselves where they could offer an explanation.

thanks,

gordon