Strip line directional coupler

A directional coupler capable of being built in strip line technology, comprising two transmission lines coupled to each other and formed on opposite surfaces of a dielectric supporting plate and the ends of said transmission lines forming connecting points and with one transmission line formed as a microstrip line with a first strip line on one surface of said dielectric supporting plate and an electrical conducting grounded line surface formed on the opposite surface of said supporting plate, and wherein the other one of said transmission lines is formed as a coplanar line and comprises a second strip line (5) mounted on said opposite surface of said supporting plate in an area (4) which is free of said grounded line surface (3) and wherein said second strip line (5) is essentially parallel to said first strip line (2) of the microstrip line and wherein said second strip line (5) and said first strip line (2) are positioned on said dielectric plate such that energy is coupled between them along their lengths so that a directional coupler is formed.