How to evaluate a antena for GSM phone?

maybe just normal requirements.such as gain,vswr,polarization,efficiency,etc.

oh. this is a good question. but deoends on the what you mean. whether:

1- comparison between antennas for the GSM or
2- evaluation for a certian antenna if it is working well or what ever.

For mobile cell we use a spherical propagation antenna... (most cases) coz mobility needs a free move for the cell and a full signal receiving andtransmitting coverage. now! depends o this, you can use any antenna that provide this condition.

for (2), evaluating antenna performance needs antenna propagation tester. which is (as i think) not available except in professional labs. so, we can change the antenna temporary and compare the changes in signal power received. if it is equal. then the antena is ok:)

for professional information please pm me or try to find out at www.epanorama.net

If your antenna is already part of the phone you have to disconnect first the RF front-end of your mobile from the antenna.
After this connect a very thin (but high quality) 50 ohms cable to the antenna. This cable (~10cm long) should be terminated with an SMA connector, allowing you to connect (using a longer cable) to Spectrum Analyzer.
Put your mobile in an anechoic chamber (for empirical measurements you can use an open field).
Use a second multi-element Yagi antenna to generate your reference signal (Vertical and Horizontal position).
For substitution method (to find antenna gain in dBd) replace your GSM antenna with a calibrated dipole. The difference in dB between antennas on your Spectrum Analyzer is your antenna gain in dBd.
To find the antenna pattern for different angles you have to rotate the phone and measure the levels at each 15 degrees.

regards