Design Of Over-moded Waveguide Directional Coupler For High Power Millimeter Wave Transmission Line

In the measurement of high-power microwave and millimeter wave power,the results of the absorption measurement method are greatly affected by pressure,flow rate,and ambient temperature of the measurement device.Therefore,the absorption measurement method has shortcomings such as time delay,low measurement accuracy,no mode detection capability.The measurement method adopting a directional coupler,which has the ability of mode detection,enabling on-line detection,high accuracy,and strong anti-interference ability,is a preferred method for high power microwave and millimeter wave power measurement.The dissertation mainly deals with the design analysis and engineering implementation of two high power millimeter wave directional couplers.One is a wideband over-mode waveguide TE01 mode directional coupler operating in the Ka band(26GHz-40GHz).Different from the conventional main waveguide,the directional coupler uses uses a quadrupole waveguide rather than a circular waveguide,which not only meet the requirements of weak coupling and high directivity,but also has a relatively strong ability of resisting parasitic mode and ability of resisting standing wave effect.The other is a compact,highly directional,directional coupler operating in the Ku-band(12GHz-16GHz)with circularly-polarized TE11 mode.Conventional directional couplers use the same aperture arrays with equally-spaced distributions.In this dissertation,a programs are written using Matlab to design a directional coupler with an array of equal-aperture apertures in Chebyshev distribution,which are designed to ensure high directionality under compact conditions.The main work and innovations in this paper are as follows:(1)The development status of high-power directional couplers at home and abroad isreviewed by referring to data,it helped me mastere the basic theories and working principles of the waveguide directional couplers,and in particular summarized the theory of multipole waveguide fields and related theories of Chebyshev distribution directional couplers.(2)The directional coupler using a circular waveguide for the main waveguide is easily affected by the spurious mode,and the test data is not effective.The TE01 mode directional coupler with a quadrupole waveguide is designed owing to the strong mode selection of the quadrupole waveguide.The characteristics make the quadrupole waveguide directional coupler has an ability to reduce the disturb of parasitic mode,thus the accuracy of the measurement is proved.The quaternary waveguide directional coupler was processed and tested.The experimental results are in good agreement with the simulation results.(3)A TE01 mode directional coupler with a circular waveguide is designed to have a same coupling as that of quaternary waveguide directional coupler.Then circular taper structures with different length and baffle metal ring structures with different inner diameter are designed.They are used to simulate the situation of generating parasitic modes and standing waves in different content.The CST simulation is used to compare and analyze the influence of parasitic modes and standing waves of the circular waveguide directional coupler and the quadrupole waveguide directional coupler.(4)A linearly polarized TE11 mode directional coupler with equal apertures and Chebyshev distribution was designed using Matlab program.The length of the whole device is controlled at 100 mm to meet the compactness condition with a high directionality.Comparing and analyzing the directional couplers with equally distributional apertures in the same length,the directivity of the directional coupling with apertures in Chebyshev distribution is improved about 15 d B.After simulating the circular polarizer in the corresponding frequency band,the circular polarizer and the linearly polarized TE11 mode directional coupler are connected together for joint simulation,and it is proved that the designed linearly polarized TE11 mode directional coupler is also suitable for the circular polarized TE11 mode.Through the work of this dissertation,a directional coupler using a novel waveguide is proposed,which can enhance the accuracy of power measurement.At the same time,the design idea of a compact high-directional directional coupler is given.These related work lays the foundation for the design of high power millimeter-wave directional coupler with better structure and performance.