A directional coupler is a functional four-port network, although one of the ports may be internally terminated. Directionality is dependent on internal symmetries and matching. For each of the four ports of the coupler, one of the other ports is isolated at another port, energy is coupled from the referenced port and the balance of the energy (after coupling losses) exits the remaining port called the "mainline" or "low-loss" port. A directional coupler, as its name implies, samples signal energy based on the direction of energy flow.
CouplingThe relative signal attentuation between an input port and its corresponding coupled port.
Coupling LossThe remainder of the input power left after accounting for coupled power and power transmitted to the isolated port.
Main Line LossThe total insertion loss in the main line as measured in a matched system. The main line loss includes coupling losses, reflection losses and dissipation losses.
Coupling ToleranceThe tolerance of the average value of the coupling in dB over a specified frequency range.
Coupling VariationThe peak-to-peak variation of coupling in dB about the average value over the frequency range.
DirectivityThe ratio of the power (in dB) measured at the coupled port when a signal is applied in the forward direction (input to output) verses the reverse direction (output to input).
VSWRVoltage Standing Wave Ratio is a measure of the deviation of impedance from the characteristic impedance of the coupler.
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