How to select an RF Directional Coupler
RF Directional Couplers are four port devices - 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. Any reflected power from the main output is coupled to the port that is terminated, resulting in minimal reflections within the device/system.
The key specifications to look for in an rf or microwave coupler are:
Frequency (MHz): This is the frequency range over which the coupler can operate while providing a constant level of coupling with minimal loss and reflection.
Coupling (dB): This is the ratio of incident power fed to the main port to the power at the output of the coupled port.
Coupling Variation (dB): The maximum peak-to-peak variation in coupling expected over the specified frequency range.
Insertion Loss (dB): The reduction in output power due to the power transferred to the coupled line.
Directivity (dB): The difference between the power level of the coupled and isolated ports. The directivity is a measure of independence of the coupled and isolated ports.
Average Power (W): The level of power that a coupler can handle while maintaining minimal reflections i.e with a matched load.
Impedance (Ohms): The impedance of a coupler must match the circuit/system it is connected to; this will minimize any reflection within the circuit/system. Usually the impedance is 50 Ohms or 75 Ohms.
Package Type: RF Couplers are 4 port devices available with various connector options – SMA, N Type, BNC etc.