In the datasheets, 1 is stated as the peak forward voltage.In order to operate efficiently, this device should have a peak RMS reverse voltage range of 420.
GBU6J-T Features
the forward peak voltage is 1 the peak RMS reverse voltage range of 420
GBU6J-T Applications
There are a lot of Diotec Semiconductor AG GBU6J-T applications of RF diodes.