Research And Design Of Reflectionless Directional Coupler

With the ever-increasing demand on flexibility of microwave wireless systems design,significant research activities and interests have been recently developed in the academic and industrial toward exploring multifunction component,such as filtering,harmonic suppression,and reflectionless.Directional coupler are critical microwave components and commonly used in wireless communication systems due to the ability of provide equal power division and orthogonal phase relation.Besides,the system dynamic range of RF front-end can be improved by utilizing reflectionless components.In this dissertation,branch-line reflectionless coupler and coupled-line reflectionless coupler are proposed,respectively.In the branch-line reflectionless coupler,?/4 open broadside coupled microstrip lines are utilized to achieve tight coupling and 90° phase relation.Moreover,two section 90°branch-line is used to realize wideband operation.To verify the mechanism mentioned above,a branch-line reflectionless coupler with operating band of 1.7–2.3 GHz is designed and simulated.The simulation result illustrated that,the proposed branch-line reflectionless coupler has a wideband operation with amplitude-and phase-imbalances less than ±1 d B and ±6°,respectively.A wideband coupled-line reflectionless coupler with a wideband harmonic suppression is proposed,which contains two channels connected similar to duplexer.The channel of bandpass coupler is achieved by the multi-layer cross stubs,which can not only introduce a compact filtering coupler with 90° phase difference,but also achieve wideband harmonic suppression.Simultaneously,the stepped-impedance microstrip line and open cross-stub are used to construct the absorptive port in the bandstop filter channel,which absorbs the reflected signal from the bandpass coupler to obtain the broadband reflectionless.a wideband coupled-line reflectionless coupler operating at 1.5–2.5 GHz is implemented and fabricated to verify the aforementioned mechanism.The measured results illustrated that the proposed coupler has the advantage of low insertion loss in the passband,low amplitude-and phase-imbalances,wideband harmonic suppression,and wideband reflectionless.