LH Transmission Line based Directional Coupler Design with High Directivity and Tight Coupling

A design of directional coupler is proposed which can be applied in communication technology like personal communication services and international mobile telecommunication. In this directional coupler, we have used two coupled line sections for coupling and connected two uncoupled left handed (LH) transmission lines as delay lines. It is shown that in this design of a 3 dB directional coupler, we are able to achieve high directivity of approximately 85 dB and tight coupling within the operating frequency range. This directional coupler is behaving like an ideal coupler. When the odd and even mode velocities are made equal at a centre frequency, high directivity is obtained. Its bandwidth is between 1.65 GHz to 1.80 GHz.