Miniaturization And Broadband Of Directional Couplers And Application In Butler Matrix

With the rapid development of the fifth-generation communication technology,the demand for RF(Radio Frequency)passive devices shows rapid and sustained growth.Due to the requirement of the communication equipment market for product portability and the trend of the wider radio spectrum range,as one of the main RF passive devices,the directional couplers need to achieve small size and broadband performance urgently.Therefore,the main research content of this paper is the miniaturization and broadband of the RF directional couplers in the range of 5G Sub-6 GHz band and their application in butler matrix,which has important academic and application value.The main work and innovation of this paper are listed as follows:Firstly,in the aspect of miniaturization of directional couplers,two novel topological structures of lumped-element directional couplers are proposed in this paper.The two novel topologies have symmetrical structures and consist of fewer components.The second structure can be used to realize both strong-coupled and weak-coupled couplers.The equations between the components’ value of the novel topology and the scattering parameters of the topological network are given by employing the odd-even mode analysis method,which is used to guide the optimization design process of the directional couplers.In the process of layout design,the planar spiral inductor is realized by irregular shape,double layer metal and symmetrical structure to improve the performance of directional couplers.Finally,a thin-film IPD(Integrated Passive Device)process based on high-resistance silicon substrate is adopted to implement the two directional couplers operating in 5G N77 frequency band(3.3GHz～4.2GHz)with a coupling degree of 25 dB.The physical size of the directional couplers are 1.25 mm×0.8 mm and 1.55 mm×0.8 mm,respectively,which is less than 1/5000 of the square of the central wavelength.The results of experiment prove that the design is feasible and effective.Secondly,in the aspect of broadband of directional couplers,an improved slotcoupled directional coupler is proposed in this paper.The improved slot-coupled directional coupler uses isosceles trapezoid to replace line width change with tapering connection,which increases the working bandwidth of the directional couplers.Besides,our paper analyzes the error term of the calculation formulas and the design limitations of the slot-coupled directional couplers,and eliminates the problem of the experimental performance degradation caused by the ground connection.Finally,the improved slotcoupled directional coupler with 3 dB coupling degree is realized by multilayer printed circuit board.The directional coupler achieves coupling degree of 3.9 dB±1.2 dB and phase deviation of 87.3°±1.6° in the frequency range from 1 GHz to 6 GHz,about 120%relative bandwidth.The results of experiment prove that the design is feasible and effective.Thirdly,in the aspect of Butler Matrix,our paper proposes two kinds of 4×4 Butler Matrix,which constructed by one of the lumped-element directional couplers and the improved slot-coupled directional coupler,respectively.The former Butler Matrix presents the layout simulation results obtained by the method of moment.And the layout size is 2.05 mm×1.35 mm,which realizes the miniaturization of the Butler Matrix.The latter Butler Matrix presents the experimental results,and the relative working bandwidth is 120%,which realizes the broadband of the Butler Matrix.