Single and multiple antenna

hi
what is the advantage of single pifa antenna used in mobile for gsm and ism purpose over the multiple integrated pifa antenna ?

Lower price, less space, better system integration.

did you know what is the optimal size of pifa antennas?

---------- Post added at 19:30 ---------- Previous post was at 19:28 ----------

why designers dont use microstrip or printed antennas instead of pifa antennas?

A full ? wave PIFA placed at the edge of a ground plane of at least same size gives possibilities for good antenna function.
In the case of a GSM cell phone of normal size, must you as designer find optimal antenna size in a much smaller volume.

Designers would get fired for such antenna ideas, at least if you is thinking about printing an antenna on main board in a GSM cell phone of bar type.
FR4 PCB is not the best material to use for low loss antennas above 2 GHz but main problem is that a such antenna would need PCB area.
Inside a cellphone is PCB area very occupied.
Same PCB volume that the antenna use in top of a bar phone is often also shared with loudspeaker, camera, flash, flash discharge capacitor, a second camera and a few push buttons.
Making a printed antenna on main board would then increase size of phone ? reduced sell.

from your answer i understood the pifa antennas does not have pcb
so are they only etched on a single metal layer?

---------- Post added at 05:29 ---------- Previous post was at 05:25 ----------

from your answer i understood the pifa antennas does not have pcb
so are they only etched on a single metal layer?

No, a PIFA is very depending of its ground plane, but the part of main PCB that have an antenna structure above, is also used for 10 other things in high density electronics. Actually is whole metallic construction in a cell phone also a part of the PIFA structure.

It is not unusual that whole PIFA structure is etched on PCB, but not same PCB as main board.
FIFA can however be etched by using only a single PCB layer.
Can sometimes be seen as BT/WLAN antenna in low cost phones but also as main GSM antenna in M2M solutions were space is almost unlimited without increasing any cost.

thanks alot