Antenna design problem

Dear all:
I have a hard problem in antenna design.I must design a GSM antenan into
volume of 60x7x5mm3. And I need the BW about 140MHz in 900MHz.

The problem is that it is possible or not. I mean that it is the limited of physic.
Or someone can show me some equation to proof it.

THKs

You can try to use the idea of a tuned antenna, to be able to cover both bands, GSM850 and GSM900.
Here is an example:
http://lib.tkk.fi/Diss/2005/isbn9512277581/article7.pdf
I’ve tried something similar and work fine. Actually my design was simple than this one, using only one SPST switch that was active for low band.

Does that link work ? it didnt work for me

the link works to me .

Dear gunajraman:
i've downloaded it ,if you still can not down , send me your email , then i would send it to you .