When the Bluetooth ant closed GSM antenna...

(1)what things must need to take care when Bluetooth and GSM antenna is closed or neighbor?
(2)if GSM and BT S21 is bad what's event will be generated?
(3)How much of the S21 is safe value?
(4)any idea can improve S21 if the placement of ant is fixed?
if everybody met the problems or had idea to slove it, reply me pls.

1. the pattern orientation and the feed/ground pins positions;
2. How bad? <10 dB is bad.
3. see (2)
4. depend on where they are placed, you can send me the spec. drawing and result, maybe I can help you.
send to my email: rfdis_bbs@hotmail.com