A novel compact easy-to-manufacture design of 20 dB directional coupler has been proposed for a high power operation within frequency band 4-12 GHz. In order to obtain the broad band frequency response a three-section asymmetric coupled strip-line directional coupler has been chosen. The periodic structures are introduced on the outer edges of coupled strip-lines for the wide-band compensation of the difference between phase velocities of even and odd modes. The successfully fabricated and tested coupler shows high electrical performances. The proposed 20 dB directional coupler provides within frequency band 4-12 GHz the coupling characteristic imbalance 0.5 dB, isolation 35 dB, directivity 15 dB and VSWR<1.35. The allowable input power of directional coupler is up to 100 W. The coupler dimensions are 39x35x26 mm.

Keywords: directional coupler, coupled strip-lines, even and odd modes, periodic structures, phase velocity of modes, lines with side coupling