How does power sensor work？

How does power sensor work, and what is the definition of the bandwidth of a power sensor? If I use a power sensor to measure the output power of a power amplifier, (for example I use a 5MHz WCDMA signal centered at 2GHz to stimulate the PA), the coupled power of the power sensor is the 5MHz channel power or it also includes the power at adjacent channel caused by intermodulation, or even includes the noise power over the entire bandwidth of the power sensor?

If I use a spectrum analyzer to observe and measure the output power of the PA, I can set the defined channel power. Will this kind of measurement be more accurate than the power sensor because it does not include the intermodulation power at adjacent channel? Then the compressed characteristic of a PA can be tested much more accurate?

Thank you very much for your comments on these issues.

BR

By design, it even includes the noise power over the entire bandwidth of the power sensor (Which is DC up to many GHz). When measuring power
amplifiers, this shouldn't be a problem, usually.