How to improve PIFA bandwidth??

[pennylsn]

pifa bandwidth

hi,

i have a design here for 900Mhz and 1800Mhz.. but i can't get the sufficient bandwidth required for GSM900 and GSM1800..
can anyone tell me how can i improve that???
and why normally i can only get good return loss for one frequency band only? and the other one will be a lot worse...

please help me!!!!!!!! thanks!!!!

regards.

 

[vfone]

Bandwidth is affected by the size of the ground plane. Reducing the ground plane can effectively broaden the bandwidth of the PIFA.
To reduce the quality factor of the structure use thick air substrate to lower the Q and increase the bandwidth.

 

[marchz]

how to open you file?

 

[MK28]

if you can reduce the Q-factor of the input impedance then it will give you wide bandwidth...

 

[pennylsn]

it is Zeland IE3D file.. u hv to open it using the software..
i've tried to increase the air-gap..
but it doesn't really works