What's the purpose of shorting radiator to ground for PIFA ?

For mirror effect (image thoery). A monopole antenna uses a ground plane for imaging. PIPA is a monopole but it is folded for space saving.

Without the short circuit the image theory still can be applied on inverted-L antenna.
But inverted-F antenna added short circuit btw radiator & ground.
What's the purpose of that short circuit ? Thanks.

The impedance matching of the PIFA is obtained by positioning of the feed point and by optimizing the space between feed point and grounded pins.

hi,

the shorting pin or wall in a MSA, that converts it into a PIFA, is for making it suitable for use at lower freq. operations.suppose a Microstrip patch of resonant length L (approx= lambda/2 length) is shorted at the corner with a shorting pin,then the resonant length (quarter-wavelength)will be along half the perimeter of the patch,i mean lambda/4 = (L+W),i.e. resonant freq. = c/[4*(L+W)],where W is the width of the patch.the position of the pin is the null voltage point.

so this way or meandering the patch shape in different ways we can have a greater effective length for the current path ,and thus we can use it for lower freq. operations.

hope i the explanation is clear.if anything is wrong plz do mention.

abhi