Sensitivity improve on Slide-phone

I have a slide-phone with inside antenna , but GSM sensitivity is only -90dbm through the radiation , i also found FPC could improve it about 3dB through outside GNDing . Could u help me and give me some adivse or suggestion to hoe to improve it.thanks

Didn't there anyone meet the problem like this?

Hi,
I have not worked on the GSM phones but I have worked on similar issues.
1) check the potential difference between the RF and the digital
2) Power supply filtering.
3) Check the NF. NF seems to be high. Check the component srf and maximum frequency of usage.

Hope this helps,
B R Madhukar