Ka-band High Power Microwave Mode Conversion And Transmission Technology Research

With rapid development of high power microwaves technology, high power microwaves especial the millimeter waves are more widely applied to national defense, industry and some other aspects. High orders modes(Hop, p>>1) or whispering gallery modes(Hmp, m>>1, p=1,2) emitted by high power millimeter waves sources are not proper for antenna radiation. For the reasons that the fields are dispersed and patterns are depicted as hollow cone, these modes need to be converted to Quasi-Gaussian form by a mode converter system. A high power microwave system cannot produce the best possible results unless the mode converter subsystem are stable and efficient, and it is accordingly vital to study the mode converter system. To get stable and efficient mode converters for gyrotron at Ka-Band, the detailed work are following:1. Two coupling configurations include bent axis and varying radius are studied firstly. Based on the coupling-wave theory, coupling equations and coefficient are deduced from maxwell equations.2. Following analysis of the entire conversion character, a Hoi-H11mode converter has snake-like axis is studied. The parameters of this converter are simulated and optimized by mode transmission and conversion software combining with HFSS. Conversion and transmission efficiency is98.1%and99.5%respectively, and the bandwidth of conversion efficiency above90%is1.26GHz. Besides, inevitable errors in processing are considered, and the relative power variation of mode H11is under0.65%while the variation of radius is1mm. It indicates this converter has the ability of high efficiency, broad bandwidth and stable.3. By the analysis of mode coupling in waveguide with profile of sine, the mechanism of mode tapers are obtained, and linear, first-order sine and high-orders sine profiles tapers are studied based on this mechanism. Aimed at the geometric length, these mode tapers are simulated and optimized by HFSS, and the results indicate that transmission efficiency is above99%within their respective bandwidth. In addition the linear taper has the broadest bandwidth that is2.03GHz among these tapers, nevertheless the high-orders sine taper has the best compactness with a1.40GHz bandwidth.4. Based on Complex Power Conservation technology, scattering matrix of the break configuration is obtained, and the methods to studied H11-HE11mode converter are analyzed. Aimed at the geometric length, this converter is simulated and optimized by HFSS, and the relative power of mode H11and E11is84.4%and15.3%respectively at30.4GHz while the geometric length of this converter is290mm. The relative power of HE11is above0.98within0.81GHz bandwidth, in addition the inevitable errors in processing and power capacity are considered. The results indicate that the relative power variation of mode HE11is about2%while the variation of radius is2mm, and the power capacity is about340MW while the radius is20mm. It indicates this converter has the ability of stable and enough power capacity.