Four Important Phrases to Know About RF Directional Couplers

Often a crucial part of the development of successful circuit systems for radios, the RF directional coupler works as a way to efficiently divert an amount of energy from a main flow to another circuit. Whether you are new to electrical engineering or an expert in the field, keep the following four phrases in mind when discussing the functions of your RF directional coupler.

Coupling Loss

As the coupler works, a particular amount of energy will be lost from the main line to the coupled port as well as the isolated port. This energy amount is called the coupling loss. The majority of the energy should travel to the coupled port instead of the isolated port.

Main Line Loss

While the larger part of the energy taken from the main line should be described by the coupling loss amount, there may be even more energy lost in the main line. This is usually through resistance caused by heating. Often, scientists will combine the coupling loss with the main line loss to explain the power which is theoretically reduced.


Directivity is the difference in power levels between the coupled port and the isolated port. This concept relates to isolation, which is the difference in power levels between the isolated port and the input port. Measurements of directivity show the engineer or scientist how independent the coupled port and isolated port are from the input port and output port.

Hybrid Coupler

Some RF directional couplers can have extra complexity from additional ports. One type of these directional couplers is the hybrid coupler, which has the ability to equally split power between two coupled ports. As you learn more and build your circuit systems, keep in mind that the power sent to the coupled ports in the coupler should always have less energy than what is contained in the main line.