Broadband multisection asymmetric 8.34-dB directional coupler with improved directivity

The paper presents the design of a broadband 8.34-dB directional coupler in a stripline technique. In order to obtain broadband frequency response a three-section asymmetric coupled-line directional coupler has been chosen. The influence of discontinuities in the regions of coupled and transmission line connections, as well as intersection connections, has been taken into account in the design stage. The parasitic reactances associated with the discontinuities have been compensated using the developed capacitive compensation technique which allows for directional couplers´ design with improved directivity and return loss characteristics. The compensation technique has been for the first time applied for the design of directional couplers with the coupling weaker than 3 dB. The designed coupler has been manufactured and measured to validate the presented compensation technique.