Research On Key Technologies Of Differential Branch-line Coupler

Branch-line coupler is one of the most important microwave compentent in RF communication system.It is usually be used in various circuits and system networks such as power amplification,RF front-end receiver system,feeding network of antenna and phase shifting network.At the same time,differential circuits become more and more popular due to their ability of high immunity to the environment noise and electromagnetic interference.Thus,differential branch-line coupler is worth to be studied.However,tradition branch-line couplers are usually single-ended designs,and no differential branch-line coupler has been reported.Therefore,in this thesis,the key technology of differential branch-line coupler has been studied.Firstly,the basic circuit model of differential branch-line coupler is proposed in this thesis.The functions of power dividing for differential-mode signals and common-mode suppression can be achieved.Based on this circuit model,the arbitrary power division at the output ports can be realized by adjusting the impedance of quarter-wavelength transmission lines.Get specific design parameters accronding to the detailed design theory and closed solution.The detailed design procedure is given in the thesis.Furthermore,the ability of bandwidth enhancement for differential branch-line coupler has been discussed.In order to reduce the size of proposed circuit model for differential branch-line coupler,double T-junction structures are utilized to realize a compact differential branch-line coupler.Then,a differential filtering branch-line coupler has been proposed for the first time in this thesis.It can be well suit for high integration of wireless communication systems.Conventionally,four baluns and filters have to be added when the single-ended branch-line coupler is required to be connected with other differential circuits,which will lead to complexity for system,and make against integration.In this thesis,fuse two devices to achieve the effect of 1+1>2 under the condition of similar size,it can reduce the number and size of device.In other words,fusion of design takes many advantages in the environment of high integration.Based on this ideal of fusion design,it can further enhance the integration of RF front-end circuits and improve the performance of the whole system.Lastly,an enabling multi-operation branch-line coupler has been proposed in this thesis,which can be applied for different system connection schemes.Compared to the single-ended and differential device,the flexibility and freedom of the device for system application is enhanced.The detailed functions,theoretical analysis and application of the enabling multi-operation branch-line coupler are given,which can fill the blank of this kind of design.To conclude,the study of differential branch-line coupler in this thesis provides theoretical and application foundation for the development of the differential RF front-end circuits.