Product Details

Bias Tee


RF and Microwave Bias-Tee:- About, Types, Application, Design:

An RF and Microwave bias tee is a three-port device used to feed combined RF and DC signals to an RF device. Bias Tee helps to set the DC (DC currents or voltages) bias point for an RF component without disturbing other components in the chain. The bias tee is like a diplexer with 3 ports arranged in the shape of a letter T, with one port passing only low frequency ( DC signal ) and another port for passing the RF signal, hence it is named as bias tee.

  • Bias Tee is used to combine DC & RF signals and transmit through a channel and also helps to segregate the DC signal from the DC+RF signal and allows only the RF signal to pass through it.
  • Bias Tee has 3 ports, The low-frequency part (port) of the bias tee is used to feed the DCbias and the high-frequency port is used to passes the RF and Microwave signals to the device. In the third port, the user will get the combined signal with bias and RF ( DC + RF).

If a signal consisting of RF and DC bias is received at the combined port of the Bias Tee, 

  • The capacitor in the RF port blocks all DC signals and allows the RF Signals to pass through it. 
  • The inductor in the DC bias port blocks all RF signals and allows only DC signals to pass-through.

The important selection specifications for a bias tee are insertion loss, group delay flatness, insertion loss flatness, and return loss between the common port and high-frequency ports, and isolation between the DC and HF port.

On this page, you will learn the following details about RF and Microwave Bias Tees.

  • What is an RF and Microwave Bias Tee?
  • Types of RF Bias Tee?
  • Applications of RF and Microwave Bias Tee?
  • What are the specifications that need to consider in the selection of a Bias Tee?
  • RF and Microwave Bias Tee Manufacturers.

What is a Bias Tee Design concept?

The basic working principle behind the bias tee is, the capacitor blocks DC and allows the AC signal to pass through it and the inductor blocks AC or RF signal and allows DC to pass through it.

  • A Bias Tee is designed by placing suitable Inductors on one port to block the RF signal and suitable capacitors on the other port to block the DC signal and both the ports are combined into a third port for feeding a signal with RF and DC.

RF Bias tees are mostly designed for transmission-line environments with the characteristic impedance of bias tee will be ( Z0 ) 50 or 75 ohms. The impedance of the chosen capacitor (XC) for the bias Tee will be much less than Z0, and the impedance of the selected conductor (XL) will be greater than Z0. ω is the angular frequency in radians per second. The reactance of the bias tee needs to choose, in such a way that it will have minimal impact at the lowest frequency.

  • Practical wide-band RF and microwave bias tees use special circuit typologies to avoid the shunt path. For the wideband bias tees, there will be using a series of Inductors and additional capacitors and resistors to prevent resonances.

RF bias Tees are available either with RF connectors like BNC, SMA female or with solder pin for the DC supply. In the RF port, customers will get many connector configurations options like BNC, SMA, 2.4mm, 2.92mm, N-type, 3.5mm, etc. As many of Bias tees are designed of the Hub mount or external applications they are packages with  RoHS and REACH compliant.

How Bias Tees Work:

Bias tees are three-port often box-like coaxial components in the shape of “T” as the name suggests. As most of the components need the DC bias to operate, Bias Tee is used in the transmission line to send the DC and radio signals over the same coaxial cable used to transmit RF signals.


  • The low-frequency port of bias tee is used to feed the DC bias and the high-frequency port used to feed the RF signals but blocks the DC signal passing through it, which may cause signal distortion and the third port is used to connect to the active device for feeding the RF and DC signal for biasing.
  • RF Bias tees are manufactured using a capacitor in one port and Inductors in the other port. In Bias Tees, Capacitor in the RF port is used to block the DC and allows the RF signal to pass through it and the Inductors in the DC port is used to block the RF and allow the DC signal to pass through.

Bias Tees as a DC block:

DC blocks are used as a reverse component of Bias Tees. DC block is used to separate the DC signal from the received RF signal which has DC signal in it.

DC block is used near to antenna and only feeds the RF signal to the antenna for the transmission. DC blocks help to prevent the flow of DC (direct current) through RF circuits or to the antenna.

  • In DC blocks capacitors in the port serve as high-pass filters to prevent the DC voltages ( 0 HZ signals) from reaching the RF and Microwave circuits.  

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Design and Application

RF and Microwave Bias Tee types:

RF bias teas are of different types on the basis of their application and operational capabilities.

SMD bias tees:

RF SMD (Surface mount) bias tees will have the footprint packages, they can handle about 0.5 A and operate up to S bands. 

Connectorized Bias tee:

Connectorized RF bias tee will have the RF connectors for feeding the RF signal and pin or RF connectors available for the DC connections.

DC bias tees:

DC Bias tees are designed to inject high DC current in the range of about 5 Amps into an RF circuit without affecting the RF signal passing through the main path of signal transmission. 

High voltage bias tees:

High Voltage RF bias tees are designed to pass the high DC voltages in the RF chain in the range of about 30-100V without affecting the RF signal. 

High current bias tee.

High Current Bias tees are used to inject a high DC current of about 10-30 Amps into an RF device without affecting the RF signal transmission. 

High power bias tee:

High power Bias tees are designed to inject high voltage and current signals into an RF device for its operation without affecting the RF signal transmission. 

Smart bias tee:

A smart RF bias tee is a device used with AISG (Antenna Interface Standards Group ) controller to transmit the signal up to the tower in antenna line devices (ALDs). The AISG controller will be the hand-held, rack-mounted type, or integrated into the base station and located near the base station.

Applications of Bias Tee:

One of the prime applications of RF and Microwave bias tees is to inject DC currents or voltages into RF and microwave circuits without affecting the RF signal passing through the main transmission line. 

Bias tees are used for many applications, where the need to provide the RF signal and DC voltage and current to a remote device were unable to run two separate cables for each.

Industrial Applications of bias tee:

  • Optical Communications
  • High-Speed Pulse Lab Experiments.
  • Satellite communication & Antenna Measurements
  • LAB testing and R&D.
  • Data Transmission with DC supply.

DC power to amplifiers:

RF Bias Tees are mainly used to provide the DC power to power amplifiers, which are mounted on the top of the tower where the antenna is placed. A bias tee is used to combine the DC power with AC / RF signal to power remote amplifiers or other devices attached to the antenna which is placed at the receiving end of the coaxial cable.

Avoid Passing DC to the receiver:

When passing the RF and DC signal over the same cable to the remote devices, the feed inductor in the bias tee help to deliver DC to active devices, and the blocking capacitor in the Bias Tee helps to keep DC not to passing through to the receiver chain. The internal blocking diode in the bias Tee prevents damage to it if the reverse supply voltage is applied to it.

Biasing the Photo-diodes:

Bias Tee is often used to bias the photodiodes like transistors and triodes, by avoiding passing of RF signal leak into a common power supply. Conversely, Bias Tee helps to avoid the noise from the power supply reaching into the signal line.

Other applications of the bias tee include DC power over Ethernet, power source to low-noise amplifiers, remote down converters, old analogue telephone service lines, some early microphones, etc.

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Basics & Selection Feature

Main specifications need to consider in the selection of Bias Tees.

When selecting a bias tees for the design applications, customers need to select the correct RF connector and DC connector type for their installation. Connectors are available with different types, sizes and coupling mechanisms, specific impedance, and frequency range.

For example, Type C connectors can be used with 75-ohm cable and satellite TV applications below 300 MHz, even though they provide constant 50-ohm impedance. 

The important properties of a bias tee are insertion loss, RF bandwidth, and a mismatch at the two RF ports, the maximum DC current, and video bandwidth of the DC port.


In RF Bias tee, It is important to select one which covers the entire frequency band of operation. Need to clearly check the lower and higher band of operation both in RF and the combined port.

Voltage & Current Rating:

The bias tees have maximum voltage ratings as per the need to select. In general bias tees available with a low voltage range of mV to high about 200 volts are available from different manufacturers.

Maximum DC current handling is also another parameter need to consider as per the application. Bias tees range from 100 mA to 10A range is available from different manufacturers.

Bandwidth and group delay:

For digital data transmission applications of bias tee, it is important to select sufficient bandwidth on both the high and low frequencies with flat group delay across the band of operation to prevent any signal degradation.

Power Handling:

Power handling for both the RF port and DC port needs to consider in the selection of Bias tees. Different power handling ranges of FR and Microwave bias tee are available from different manufacturers. Need to select a bias tee, which can handle both in RF and combined port with higher power handling than the maximum power expected to flow through if.

Insertion loss and Impedance: 

Need to select a bias tee with lower insertion loss when it is used to feed the RF with DC signal to any other device and the impedance should match to the source impedance to avoid any internal reflection. There are 50 ohm and 75 ohm RF bias tees are available in the market from different manufacturers.

RF & DC connectors:

RF and DC connectors of the bias tee need to select as per the application where it is going to use. The size of the bias tee is another factor that needs to consider in the selection process.

In general DC connector will come with a pin or with a solder type interface, however, there are manufacturers available who offer bias tee with RF connectors like BNC for the DC bias for the quick connect and disconnect type applications.


The bias tee is a critical competent in any communication system where need to bias any device in the system.

The critical key parameters for the selection of a bias tee are current and voltage requirements, size, and cost. To select a suitable bias tee, first, need to identify a bias tee meeting the frequency range and then determine the one which meets other critical parameters.

Below is the list of top-rated RF and Microwave bias tee manufacturers listed with RFMWC, who make a different range of bias tees for your applications. If you would like to suggest any manufacturer or any specific bias tee, feel free to recommend to us through the manufacturer registration or the submit article button on the top of this page.

Thanks & Regards

RFMWC:- RF & Microwave Community

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