a simple question, what is the bandwidth of the antenna?

Hi, everyone. I do have a simple question about the bandwidth of the Antenna? For example, the lamde/2 dipole, slot antenna, or microstrip antenna and PIFA. Thanks.

And what's the dominant factor to determine the antenna bandwidth? Thanks

IEEE Bandwidth definition: "the range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard".I do not think there is agreement regarding the bandwidth of an antenna. Some people say is the -5dB bandwidth of the return loss. Some say -10 dB. For some is more important the gain.

in a general sence you can say the bandwidth of an antenna means the range of frequencies over which the antenna will work properly.
now if you see the the othere things , lamda/2 , slot antenna or the microstrip antenna these indicates the shape of the antenna ,

any designer can define his owner bandwidth: so you can consider the frequency ranger over wich the gain is within 3db, or any ather parameter within 3dB.
For commun use, we think about the band in wich the SWR is les than 2.