What antenna is good for mini wifi tag?

I am designing one wifi tag,and using PCB as antenna,but the distance is much shorter than EVM board. Because the size and room is very small for antenna,so I want to choice antenna chip,the size is smaller than 8x2x1mm.

What antenna chip is good for me?



Thank you!

Simplest antenna is a monopole, were ground is mirroring the antenna. Ground plane dimensions is equal important as the antenna space from antenna functional view. Now we can guess what ground plane size your PCB have, and antenna space relative to ground dimensions. Environment? TX/RX?
If you is the designer, why not start with designing antenna space according to your performance requirement before you fill up PCB with other components?
Antenna is the only component that not easily can be resized or relocated on PCB without consequences for the whole construction performance. I recommend that you remake the PCB and make a full PCB dipole on PCB, 15*40 mm is enough space to make a decent antenna, and then relocate battery and chip to remaining 2*3 mm PCB area. If your WiFi chip not fit in that space is a simpler problem to solve then shrinking antennas without loosing performance, and that space ratio seems as a better balanced design.
If you find resulting performance too good with that size of antenna, cut half a way, else not.