Patent ID: 7567146

Claim:
A directional coupler comprising an input port, an output port, a measurement port, a transmission path with a transmission conductor, a signal ground and their interspace to lead a signal to be measured from the input port to the output port and a first sensing conductor being located in the interspace parallel to the trans-mission conductor for forming a coupling signal in proportion to the strength of a signal propagating on the transmission path, the head end of which first sensing conductor is coupled to the measurement port of the directional coupler, wherein in the interspace of the transmission path there is further a second sensing conductor parallel to the transmission conductor both the first and the second sensing conductor are substantially shorter than a quarter wave corresponding to an operating frequency the head ends of the sensing conductors are connected to each other and to the measurement port by a measurement conductor, and the sensing conductors are coupled from their tail ends to the signal ground and designed and located so that coupling signals caused by a reverse signal are substantially equal of their level and oppositely phased in connecting point of the sensing conductors to cancel them out.