dual planar inverted antenna(pifa) for wlan

hi

i am doing project about dual frequency planar inverted f andtenna for wlan application (2.4 and 5.5 ghz) antenna and i am facing some problems about the feeding and parameters calculations and i want to use coaxial feeding probe.

this is the type of design i want and when i simulate it it doesnt show the the desired dual frequency. any one know what the problem is?
PIFA.zip

No surprise - this is a normal PIFA with a single resonance frequency.

so how to make it dual frequency?

I would try to get this book: "Multiband integrated antennas for 4G terminals" published by Artech House

Here is one dual band PIFA approach quoted there:
http://ir.lib.nctu.edu.tw/bitstream/.../010337008.pdf