有关用spectrum analyzer测量天线的问题

你好，
我是英文教育的。
When we use spectrum analyzer to measure antenna receive power for gain calculation, i find out that the spectrum analyzer can measure few kind of powers like channel power, average power and total power. So which kind of power should i choose?
当我们用spectrum analyzer测量天线的时候，我发现那个spectrum analyzer可测量几种power，有channel power， average power 和 total power。我应该选那一种power?
During the measurement with the spectrum analyzer, is it a must to see a peak in the receive power vs frequency plot? I found out that it still showing some power value even the screen does not show a peak.
How much the frequency span i should set?
谢谢！