A directional coupler is a passive electronic device, whose basic function is to operate on an input signal and produce two output signals. This is typically done by employing two transmission lines in close proximity, such that the energy flowing through one is "coupled" to the other.
Key Characteristics
The key characteristics of a directional coupler are its operational bandwidth, the range of frequencies over which its performance falls with specified limits, and main-line loss and directivity. Ideally, a directional coupler should sample the energy moving in the forward and reverse directions, and keep the two separated.
Main-line Loss
The main-line loss, or main-line insertion loss of a directional coupler is the change in power caused by the insertion of the coupler into a transmission line. It includes the effect of power transferred to the coupled line.
Directivity
Directivity is the difference between the power transmitted, measured in decibels (dB), in the desired direction; and the power transmitted in the opposite direction at a coupled port. Directional couplers typically have directivities between 20 and 40 dB.
Tags: directional coupler, main-line loss, power transmitted