Patent attributes
A directional coupler with two sensing conductors and a basic coupler and a supplementary coupler corresponding to them. The basic coupler is based on the coupling between a first sensing conductor (421) and the transmission conductor (410), and the supplementary coupler is based on the coupling between a second sensing conductor (422) and the transmission conductor. The sensing conductors are substantially shorter than a quarter wave, because of which the directivity of both the basic and the supplementary coupler is low. The other ends of the sensing conductors are connected to each other and further to the measurement port of the directional coupler. The coupling signals caused by a reverse signal in the connecting point of the sensing conductors are arranged equal by their absolute value but oppositely phased, in which case their sum signal in the measurement port is insignificantly small. For this purpose, for example, the transmission line formed by the first sensing conductor and the ground is terminated with a matching element at its opposite end, and the transmission line formed by the second sensing conductor and the ground is left open at its opposite end. The termination impedances can be adjustable and the directional coupler thus tunable. In this manner, the directivity of the total directional coupler is improved by means of the second sensing conductor. The directional coupler is small-sized, and good directivity is achieved in a very large frequency range.
