The Research Of Terahertz Waveguide Directional Coupler

With the continuous development of terahertz technology,the demand for high-sensitivity powermonitoring systems and high-power signal sources in the terahertz band is increasingly urgent.The directional coupler is a passive device that can realize directional power distribution which is a very important part of monitoring systems and high-power signal sources.This paper studies the directional coupler from three aspects of theoretical analysis,design and simulation,fabrication and experiment.Three different structures of the terahertz waveguide directional coupler were designed.Firstly,the research background of terahertz directional coupler and the current research progress are briefly introduced.Subsequently,the transmission characteristics of the rectangular waveguide and substrate integrated waveguide(SIW)were analyzed.Using the coupling theory,the characteristics of the three coupling structures of the branch line,the H plane slot and aperture coupling were analyzed.The correspondence between the coupling degree,the isolation degree and the key structure size of the coupler was obtained.Three terahertz waveguide directional couplers operating in 320~380GHz were designed and simulated by using CST MWS 2013.The influence of critical structural parameters on coupler performance was discussed.The first coupler is a branch line coupler based on metal rectangular waveguides.The structure of a four-branch line bridge is used.The influence of the number,length,and width of branch line on coupling and directivity is discussed.The structure of the coupler is optimized.The coupling degree of the coupler is 3dB,the directivity degree is greater than 12 dB,and the output amplitude unbalance is less than 1dB;The second coupler is a H-plane slot waveguide directional coupler which is improved by setting two curved waveguides intersecting at the center to form a coupling slot,thereby the step-like structure which is difficult to manufactured can be replaced.The impedance matching performance and bandwidth of the coupler are improved.The relationship between the curvature radius of the waveguide,the slot length and the coupling degree,directivity is further discussed.The coupling degree of the coupler is 3dB,the directivity degree is greater than 12.3dB,and the output amplitude unbalance is less than 1dB.The third type is an SIW based aperture coupler.Two rows of staggered coupling holes are set on the common metal was of two vertically aligned SIWs for coupling.The correspondence between the coupling hole diameter,spacing,distance to narrow wall and coupling and directivity is discussed.The coupling degree of this coupler is 20 dB,directivity is greater than 10 dB,the output amplitude imbalance is less than 1dB.The H-plane slot waveguide directional coupler was manufactured and tested.The test results show good agreement with the simulation results.The possible causes of the test error were analyzed.In summary,the terahertz waveguide directional coupler designed in this paper has good performance and has important application value in the terahertz circuit system.