ABSTRACT
Directional couplers are used for many RF and microwave applications to function as attenuator, power splitter, hybrid junction, and most commonly a sampling device for measuring forward and backward waves on a TL. TL directional couplers give lower profile and are very popular due to their several advantages, including manufacturability, repeatability, and low cost. In the design of directional couplers when they are used as sampling devices, the key design parameters that the designer needs to give special attention are directivity, VSWR, coupling level, and insertion loss. The directivity is a measure of how well the coupler can isolate two signals. Higher directivity results in better measurement accuracy. As a result, it is the most critical design parameter for accurate measurement systems. In practice, port termination impedances, coupling level, and operational frequency are the input design parameters that are being used to realize couplers.
