A type of diplexer, bias tees serve an important role when you want to supply DC currents or voltages to RF devices. The components are designed as three-port, coaxial components that accept DC voltage from a power supply. The bias-T circuit is simple: it consists of one inductor and one capacitor. The “tee” in the name is derived from the shape of the three ports, which is typically in the shape of a T.
Bias tees combine low frequency (DC) and high frequency (RF) signals into a common port (RF+DC). The low frequency port is used to set the bias; the high frequency port passes the radio frequency signals but blocks the biasing levels. The bias tees components consist of passive RF circuits that provide DC bias to an active device, allow the insertion of direct current (DC) voltages into a signal path without disrupting the existing signal in that path.
Bias tees are designed to operate over a range of signal frequencies; the reactances are chosen to have minimal impact at the lowest frequency. They 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.
Typically, bias tees are used with active devices that are also remote, such as a satellite dish. By allowing the active device to receive signal and power over one set of cables instead of two, bias tees reduce the number of cables that are required.
Bias tees are used when you want to add a source of DC power or control signals to an RF line. They are used to power up a transistor, a photodiode or a low noise amplifier that typically are at the end of an RF line. A common bias tee application is powering a remotely located active antenna or low-noise amplifier through an RF coax line. Similarly, bias tees are used to tap DC off an RF coax line with existing DC feed.
Typical applications that use these components include:
In RF and microwave designs, frequency mixing is one of the most critical sections in the signal chain. They are used in a variety of RF/microwave applications, including military radar, cellular base stations, electronic warfare, C4ISR, Missile Defense, CNI, space applications, manned/unmanned military aircrafts, and ship-to-ship communications.
In today’s market, RF designers are working with more advanced applications that need frequency- mixing solutions which are customized for each application, optimized for performance, and support the common platform-based designs. In general, most designers now want wideband performance, increased linearity, higher integration with other components in the signal chain, and lower power consumption. Different industries and markets place different priority on these criteria and selection of mixer types often deciding between tradeoffs for particular applications.
Bias tees are offered in different connector types (including SMA and Type N) and in varying frequency ranges.
A standard three-port network for general purpose applications.
High Current Bias Tees/ SMA Connectors
A standard three-port network for high current applications.
Pulsed bias tees balance RF performance with strong power-handling. Pulsed bias tees allow a current pulse to reach the amplifier with minimum distortion across multiple frequency bands. They are designed for rigorous usage without sacrificing RF performance.
A standard three-port network specific for 75 Ohm applications