A bias tee is a T-shaped isolation circuit used to separate supply voltages for RF components or low- frequency signals from high-frequency signals. It represents a crossover and is also referred to as a remote supply crossover. Such bias tees are used in front of RF amplifiers and RF preamplifiers on radio masts, where they separate the supply voltage fed in via the RF cable and feed it separately to the amplifier.
Remote feed crossovers are available for all frequency ranges up to 50 GHz and higher.
In the simplest case, the RF signal and the DC voltage or the superimposed low-frequency signal are fed to such a bias tee. The high frequency is separated by the capacitor, the low frequency or supply voltage by the coil. The series connection of the coil and capacitor also acts as a low-pass filter, separating the high frequency from the low-frequency output.