Description
Bias tees are a type of diplexer, playing a central role when one wants to supply DC currents or voltages to RF devices. They are three-port coaxial components designed to accept DC voltage from a power supply. The circuit of a bias tee is not complicated, it includes an inductor and a capacitor. The “tee” in the name comes from the fact that the three ports of the component are often arranged in the shape of the letter T.
Bias tees function by combining low frequency (DC) and high frequency (RF) signals into a common port (RF+DC). The bias is set by using the low frequency port; the high frequency port passes the radio frequency signals but blocks the biasing levels. The components consist of passive RF circuits that provide DC bias to an active device. This allows the insertion of direct current (DC) voltages into a signal path without disrupting the existing signal in that path.
Bias tees are used to supply an active device such as an antenna amplifier, laser diode, photodiode, or optical modulator with a bias current or bias voltage while allowing high speed, RF signals to pass through with minimum signal degradation. Bias tees are commonly used with active devices that are also remote, such as a satellite dish. They allow the active device to receive signal and power over one set of cables instead of two, reducing the number of cables required.
Applications and use cases
Bias tees are used for adding a source of DC power or control signals to an RF line. They function in powering up transistors, photo diodes or low noise amplifiers that commonly found at the end of an RF line. A typical bias tee application is powering a remotely located active antenna or low-noise amplifier through an RF coax line.
Typical applications utilizing bias tees:
- Providing bias to amplifiers inside of complex systems, like base stations and radios, as well as biasing discrete transistors or packaged devices in test and measurement applications.
- Inserting DC power into an AC signal to power remote antenna amplifiers or other devices.
Bias tees are offered in different connector types (including SMA and Type N) and in varying frequency ranges.
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