Design of broadband strip-line directional couplers with improved directivity

The theoretical and experimental results for two designs of 6-dB directional couplers operating within frequency band 2 - 8 GHz are presented. The both directional couplers are based on the coupled strip-lines. The couplers show high electrical performances as well as compact size, low weight and easy-to-manufacture design. It is shown that the directional coupler with periodic structure of step discontinuities on the outer edges of strip-lines has the better isolation and directivity in comparison with the coupler without periodic structure. The improvement in directivity and isolation is 6 dB at the high frequencies.