Research On High Power Millimeter Wave Measurement System

The high power millimeter-wave power measurement system is a necessary guarantee for the performance test of high power millimeter-wave source.At present,the high power millimeter-wave measurement system consists of a water-load measurement system and a directional coupler measurement system.The core device of the water-load power measurement system is high-power capacity water load,which utilizes the strong absorption of waves by water to achieve energy conversion from electromagnetic energy to thermal energy.The directional coupler detection system achieves on-line envelope monitoring,spectrum analysis and other functions through energy coupling,and its core device is a broadband directional coupler.In this article,we mainly focuses on the core devices(water-load,directional coupler)in high power microwave and millimeter-wave measurement systems.The second chapter develops the theory of wideband water load and waveguide directional coupler.Firstly,geometrical optics analysis method is proposed and used to simplify the trajectory analysis of electromagnetic ray within water loads.Comprehensive analysis of the influence of the dielectric constant,thickness,and water loading height on the trajectory of ray is conducted.Then,according to the principle of phase cancellation,the formula for water-load material thickness calculation is deduced when phase compensation occurs.The theoretical design of low VSWR and wide-band water load is realized.Finally,the basic principle of waveguide directional coupler: the principle of pinhole coupling and phase superposition is briefly described,and formula derivation is made for the design of equal-aperture and equal-distance directional coupler.In the third chapter,the design of Ku,Ka and Ka-Q band water loads and Ka-band periodic structure dry load are completed.Firstly,according to the principle of phase cancellation,the thickness of the water-load material is calculated when phase cancellation of TE01 mode occurs,and then,modeling and simulation are performed using HFSS.Simulation results show that the designed water load has the advantages of wideband operation:-35 dB bandwidth of Ku-band quartz material water-load is 6GHz;-40 dB bandwidth of Ka-band quartz material water-load is 14GHz;-40 dB bandwidth of Ka-Q band PTFE water load is 24 GHz.In simulations,the frequency point of phase cancellation obtains the minimum reflection parameter in the working band,which further validates the reliability of the geometrical optical analysis method and the phase cancellation principle in the broadband water load design.Secondly,the paper proposes three new types of water load structures: double-cone structure,spiral diversion structure and helix structure.The effect of new water load structure on power capacity is verified by fluid analysis.Finally,a new periodic dry-load is proposed.In this periodic structure,copper and silicon carbide are arranged alternately.This structure can effectively compensate for the lack of thermal conductivity of silicon carbide materials,and reduce the effect of copper on the dry load standing wave characteristics.Through the joint simulation of electromagnetic and thermal steady state,the height,the ratio of silicon carbide to copper,and the heat dissipation structure are optimized.Simulation results show that the reflection parameter is less than-30 dB in Ka band and the average power capacity is greater than 10 kW.Finally,a novel Ka-band,high-flatness,wide-band directional coupler is designed using the pinhole coupling theory and phase superposition in the fourth chapter.The use of a non-standard rectangular sub waveguide structure instead of a standard rectangular sub waveguide is advantageous in reducing the size of the directional coupler and achieving miniaturization.At the same time,the medium-loaded auxiliary waveguide structure can eliminate the higher-order mode content in the auxiliary waveguide and reduce the fluctuation of the coupling degree.The simulation results show that the coupler S11 is less than-40 dB in the 26-40 GHz band,the coupling degree is about-48.6dB,the in-band fluctuation is ±0.2dB,and the directivity is greater than 25 dB.In Chapter 5,the cold test,thermal test and temperature environment experiment of water-load are carried out.The results show that water load with quartz material and biconical structure have a reflection parameter of less than-25 dB in the range of 26.5-40 GHz in clod test.Under the condition of input power of 400 kW,the water load is continuous for 4 hours without abnormality.Ka-band water load with PTFE material and helix structure has a reflection parameter of less than-40 dB in the range of 26.5-40 GHz.Finally,summary of this thesis is conducted.