What is RF coupler and how to choose RF Coupler?

  • What is RF Coupler?

RF and Microwave couplers are passive devices that divert / couple a fraction of the signal from the main transmission line to another coupled transmission line. The signal output at the main port of the transmission line is called the “direct or through” signal and the other transmission lines (Coupled line) is called the “Coupled signal”. RF signal in the main transmission line remains the same as the input signal and the RF signal at the coupled port is attenuated by the coupled value of the coupler.

· If the signal at the coupled port is travelling in the same direction as the input signal, it is called a “forward-wave” coupler.

· If the signal at the coupled port is travelling in the opposite direction, it is called a “backwards-wave” coupler.

· If the outputs signal of the through and coupled ports are equal in amplitude, then this coupler is called a “hybrid coupler”.


  • What is a directional coupler?

- Directional Coupler: This is a four port device – with an input and output port, a port for the coupled signal and a port that is terminated internally. The power that is passing from the input to the output is coupled with a coupled line and passes out through the coupled output port, which is isolated from the main output port.

  • What is the RF coupler used for?

The RF coupler is used to measure of reflected power (degree of mismatch of the load) by sampling the reflected wave at the coupled port. When the RF coupler is connected to the transmitter output, we can monitor the VSWR of the antenna system. RF coupler is used for adjusting the VSWR by lowering the power in the coupled port.


EASTEVER's RF couplers are available in directional couplers, dual directional couplers, hybrid coupler and unequal split power tappers product designs. Many of our RF couplers and tappers are RoHS and REACH compliant. Couplers from Eastever can be purchased in N or SMA cofigurations, unequal RF tappers are available with 7/16 and Type N connector models. These precision couplers and tappers for RF are quality manufactured to precise specifications required for accurate coupling at the specified values listed for each product.

Eastever's directional couplers come in N ,F or SMA, while dual directional couplers and hybrids are available in SMA only. Power ratings for Eastever RF and microwave couplers range from 10 Watts to 70 Watts and power tappers handle high power up to 300 watts depending on style. Frequency ratings for our coaxial couplers range from 1 GHz to 8 GHz, unequal RF tappers are more wide band with 380 MHz to 6 GHz based on model selected. Our RF couplers can be ordered with various directivity (dB) from 3 dB, 6 dB, 10 dB, 16 dB, 20 dB, 30 dB and 35 dB, while RF unequal tappers have 4.8 dB, 5 dB, 6 dB, 7 dB, 8 dB, 9 dB, 10 dB, 11 dB, 12 dB, 13 dB, 15 dB, 16 dB, 20 dB, 30 dB depending on model.


  • What are couplers in power transmission?

In general, couplers are designed by a pair of coupled transmission lines, in which RF power on the coupled line and mainline flows in the opposite direction. The mainline connects ports 1 and 2 and the coupled line is connected between ports 3 and 4.


  • Main specifications need to consider in the selection of RF Coupler.


The frequency range of the RF coupler indicates the frequency over which the coupler can operate with minimal loss and reflection while used in an RF and Microwave circuit.


Coupling of the RF coupler indicates the ratio of the RF power fed to the main port to the power output at the coupled port of the RF and Microwave coupler. Values will be coming as 3 dB, 6dB, 10 dB, 20 dB etc

Coupling Variation: 

Coupling variation is the maximum expected peak-to-peak variation in the coupled signal power over the specified frequency range of its operation. It is represented in dB, 0.2 dB over the band of frequency is acceptable.

Insertion Loss: 

Insertion loss indicates the reduction in RF power at the output port during the power transmission through the coupled line of the RF coupler. It is expressed in dB, 0.2 dB over the coupler is acceptable.


Directivity of the RF coupler indicates the difference in power level between the coupled and isolated ports. The directivity is measured in dB and it indicates the independence of the isolated and coupled ports of the RF coupler.

RF Input Power:

Power handling of the coupler is one of the prime features that need to consider in the selection of the RF and Microwave coupler. The power handling capability of the coupler main line should be higher than the maximum power expected to pass through the RF and Microwave coupler. The Average Power in watt indicates the level of RF power that the coupler can handle while maintaining the electrical characteristics of the coupler.


The impedance of the RF and Microwave coupler must match with the remaining circuit to minimize any reflection within the system. Usually, the impedance of the coupler will be 50 Ohms or 75 Ohms. Need to select the coupler accordingly.

Operating Temperature Range:

The operating range of the RF coupler indicates the temperature over which the RF coupler will work without any variation in its electrical characteristics. In general -40ºC to +85ºC is ideal for the coupler operation. For the specified applications, need to select the RF and microwave coupler as per the required environmental operating temperature range.

RF Connectors:

RF and Microwave couplers are available will most of the connectors like SMA, BNC, N, TNC, and also waveguide couplers are available. Need to select the coupler as per the application in the circuit.

Physical Size:

The physical size of the coupler and the position of the mounting screw need to consider in the selection of the RF coupler for any specific applications.



James  Wang

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