A design of single and multi-section microstrip directional coupler with the high directivity

In this paper, single and two-section microstrip directional couplers are implemented for realizing the high-directivity characteristics. The achievement of the high-directivity with microstrip configuration is carried out by the distributed capacitor to decrease the even and odd mode phase difference. Capacitive compensation is performed by gap coupling of open stub formed in sub-coupled line. Therefore, insertion loss and power handling capability are not affected by the gap coupling. The proposed structure is easy to fabricate and incorporate another microwave device due to planner microstrip. We designed and fabricated single and two-section directional coupler with 20 dB coupling. In spite of microstrip structure, the capacitive compensation structure shows the 30 dB (1.6 GHz-2 GHz range) and 26 dB (1 GHz-2.5 GHz) of directivity in single and two-section directional couplers, respectively. Experimental results show a good performance with excellent directivity characteristics.