Bias tee

Updated September 21, 2011

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Bias tees are used to supply DC currents or voltages to RF devices, such as the FETs that are used in amplifiers. Bias tees are everywhere, from your cell phone's power amp to the front panel of your network analyzer. A bias tee is a classic example of a diplexer. In the figure below, an RF signal incident to the upper right port (labeled RF & DC)is delivered only to the upper left port (RF only). A DC signal (or very low frequency, or video, signal) can be passed from the upper right port to the lower right port (DC only). Properties that are important to a bias tee are RF bandwidth, insertion loss and mismatch at the two RF ports, the maximum DC current, and video bandwidth of the DC port.

Check out our example of a bias tee design using quarter-wave transmission lines.