Research And Design Of High Directivity And Ultra Wideband Directional Coupler

Directional coupler can be considered as a kind of microwave / millimeter wave components in modern communication system,it can be used to divide or combine the power of signals within a certain frequency range according to a certain proportion,and has a direction.Directional couplers have many kinds of structures.In recent decades,many experts and scholars have successfully designed the directional couplers of different advantages based on stripline,microstrip line,coaxial line and waveguide.The directional coupler based on stripline and microstrip line has the widest bandwidth,and the stripline directional coupler can get higher directivity than the microstrip directional coupler because of working in TEM mode.Therefore,in the case of low power requirements,the stripline directional coupler is the most widely used.The synthesis method and related design chart of directional couplers have been researched and explored by experts and scholars for decades,and have been mature in theory.But its theoretical formula is too complicated and the design chart is not perfect.It can not meet the needs of engineering design because of covering only some typical design data.The requirement of bandwidth ratio of directional coupler in modern communication system is increasing.When the working frequency of the directional coupler is increased to the microwave or even the millimeter wave frequency band,the isolation and VSWR between each ports will continue to decline,and even close to zero so that the directional performance will be lost.Therefore,in order to achieve high directivity and ultra wideband performance of directional couplers,the related research and improvement are still indispensable and urgent.On the basis of the existing theory,this paper carries on the popularization and the innovation research,and summarizes all kinds of design methods of the directional coupler which can meet the needs of practical engineering.We also developed symmetric and asymmetric,Chebyshev tapered transmission line directional coupler,and improve the directivity index method is proposed to improve.Through several practical test,the validity and applicability of the design method is proved.