antenna troubles, pls help!!

when I debug my handset, I found one trouble. when I fitted the antenna and then transmited, the mainboard shut off, but I got off the antenna and transmitted, the mainboard would work and didn't shut off.
thanks!
gqwhut@hotmail.com

shut off ? Can you describe it more clear ?

yes. Shut off, I mean, the mainboads automatically power off.

It sounds as if yor antenna is badly matched, and/or missing a balun. This will cause high circulating currents to be induced into the rest of your board. This often causes them to freeze, reset or shut down.

What type of antenna are you using? Can you post a picture or drawing of it?

Did you use any matching circuits in Tx path including PA & antenna matching ? Try to move shunt components and test it again.

In this case the antenna could be ok (assuming a good antenna match).
The problem could be a lack of RF shielding or a poor ground design of the layout. The circuits affected by the RF power that cause this phenomenon could be the BB processor or the Power Management chipset

Thanks, I shot the trouble by adding a filter betweent the power supplier and the mainboard. So Vfone is right.
Thank you, averyone

Before I had found 26dBm transimit power can let the microcontroller run out again and again. Later I found the microcontroller circuit was not properly shielded.