Miniaturized broadband three-section symmetrical directional coupler with reduced coupling coefficient requirements

A novel design of a miniaturized broadband three-section directional coupler is shown. The applied exchange of transmission and coupled ports of a middle section allows for the reduction of required coupling coefficient. Two different techniques reported in literature have been utilized to miniaturize the presented structure. The proposed approach has been verified by the design of a 3-dB directional coupler. The measurement results are in good agreement with the ones obtained from electromagnetic calculations. The manufactured coupler features wide operational band (0.8 GHz to 3.5 GHz), in which return losses and isolations are better than 18 dB.