Why Minimum Return Loss is -3dB?

In antenna design, the minimum return loss is -3dB? Can I know why is -3dB? And how to relate return loss to the performance of the antenna?

Best regards

A return loss of 3 dB (its normally written as a positive number, not negative, as we are talking of a loss, not a gain) is very poor. But without a crystal ball, nobody can help you. You will need to give full information about the antenna design, size, frequency,. how you get the return loss (measured or simulated).

The reflected power can go from nearly all to none. It all depends upon the antenna impedance and the transmission line impedance.