Research On High-frequency Systems Of Microstrip Meander-line Planar Traveling Wave Tube

Microstrip meander-line(MML)planar traveling wave tube(TWT)is developed on the conventional microstrip structure.Compared with helix TWTs,coupling cavity TWTs and other conventional TWTs,it has smaller volume and lower operating voltage.Meanwhile,it can be miniaturized and mass-produced by photolithography and deep reactive ion etching(DRIE).Therefore,MML TWT can be applied to the high frequency(HF)where the size of slow-wave structure(SWS)becomes very small.Besides,it has potential in the integration of TWT as well.However,MML TWT also has some disadvantages of low interaction impedance,narrow operating band width and high possibility of charge accumulating on dielectric substrate.In this thesis,the machining process and transmission characteristics test results of two MML HF systems will be presented,and a dual-beam power integration scheme for one of them will be proposed.In addition,the application of semiconductor films in MML HF systems will be explored.The research contents and results are as follows.(1)This thesis introduces the design and machining of a HF system of U-shaped MML with conformal dielectric substrate.The problem of dimensional accuracy of SWS brought about by mechanical faults was deeply discussed,and the corresponding solutions were put forward.Furthermore,the transmission characteristics of two batches of SWS were tested.The test results show that the machining of both the SWS and the input/output structure have good consistency,which means they have the great potential of mass production.In the range of 90-102 GHz,the loss per unit length of SWS is 5.83d B/cm to 7.74 d B/cm.In general,the HF system has good transmission performance.(2)Two kinds of U-shaped MML HF systems with different microstrip-waveguide coupling structures were fabricated.Their transmission characteristics were tested respectively and the test results were analyzed.The test results show that at 90-102 GHz,the S₁₁ of both HF systems are below-20 d B,and the S₂₁ can basically reach above-5d B,and the loss per unit length is between 7.5 d B/cm and 10.5 d B/cm.For one of these two HF systems,a dual-beam power synthesis scheme was proposed,and the parameters of output power,gain and electronic efficiency before and after power synthesis were compared.After power synthesis,the output power can reach 59.19W at the central working frequency of 96GHz,which is 79.4%higher than that before power synthesis.The corresponding gain is 21.7d B and the electron efficiency is 8.9%.(3)The performance of ZnO films on MML SWS was investigated.The ZnO film was prepared by magnetron sputtering.To find its conductivity,its square resistivity was measured by using four-probe method,and the conductivity was thus found to be of the order of 10^-4 s/cm.Meanwhile,two MML SWS with different periods was processed and the dispersion characteristics were tested before and after coating,which was proved that the ZnO film has little effect on the dispersion characteristics of the designed HF system.Finally,by transmission characteristic test,it was proved that the ZnO film has little influence on the transmission performance of the designed HF system as well.