As the name implies, directional couplers sample signal energy based on which direction energy is flowing in. They are invaluable items for measuring power levels of signals in microwave systems. A directional coupler is a passive device that is utilized in radio technology, and couple a certain amount of electromagnetic power in a transmission line to a port. This occurrence allows the signal to be utilized in another circuit.
An important characteristic of directional couplers is that they only couple power that is channelling in one direction. These devices are most often made from two coupled transmission lines that are positioned close enough together that power that passes through one is coupled to the other.
Applications of Directional Couplers
Directional couplers from Werlatone are important components in a variety of RF applications, especially for measurement applications. Many different directional couplers are available from all sorts of manufacturers, such as stripline couplers, coaxial configurations, and waveguide couplers. For broadband applications, stripline and microstrip couplers are most suitable.
While many methods have been proposed for the purpose of broadband, the predominant mode is limited at a lower frequency by the cutoff frequency, and the higher order modes limit the higher frequency extensions. If bandwidth requirements are not crucial, coaxial directional couplers that use air dielectrics are a typical solution, and are suitable for the low-loss performance.
There are many applications of directional couplers, including:
▪ Providing signal samples for monitoring
▪ Combining feeds to antennae
▪ Forming antenna beams
▪ Providing taps for cable-distributed systems
▪ Separating signals on telephone lines
Directional couplers are functional four-port networks; however, one of the ports can be internally terminated. The directionality of the coupler depends on internal symmetries. Energy is coupled from the referenced port, and the balance of the energy leaves the remaining port that is referred to as the “mainline” port.
There are various parameters for directional couplers, including the following:
▪ Coupling Loss
▪ Main Line Loss
▪ Coupling Tolerance
▪ Coupling Variation
By applying what is known by the finite-element method (FEM) of analysis, engineers can effectively design asymmetrical rectangular directional couplers for high power applications, considering the impact of metallic diaphragms that partly separate the inner conductors of couplers. These metallic diaphragms allow engineers to simply modify the coupling factor. These couplers can be achieved without significant challenges and feature easy, cost-efficient mechanical construction.
High quality directional couplers offer the bandwidth, high directivity and higher power that are often required for the highly demanding applications, and are RoHS and REACH compliant.