Astigmatism in tapered slot antennas

A series of scale model measurements of transverse electromagnetic mode tapered slot antennas are presented. They show that the beam launched by this type of antenna is astigmatic. It is shown how an off-axis spherical mirror can be used to correct this astigmatism to allow efficient coupling to quasi-optical systems. A millimetre wave antenna and mirror combination is described and, with the aid of solid state noise diodes, the coupling of the launched beam to a quasi-optical spectrometer is shown to be in good agreement with that predicted by the scale model measurements.     

95 GHz回旋管内置准光模式转换器仿真设计

 高功率毫米波回旋管输出的高阶模式不利于空间传输,必须进行模式转换。由于不便采用波导模式转换器,因此对内置准光模式转换器进行了研究。内置准光模式转换器由Vlasov辐射器、准抛物柱面镜和相位修正镜组成。基于标量衍射理论和KSA算法,编制了数值模拟程序,设计了相位修正镜。计算分析了参考平面处的场分布,表明该准光模式转换器的标量转换效率大于98%,矢量转换效率大于93%。计算结果表明,该方法可以高效地指导准光模式转换器的设计。     

Selective excitation of high-order modes in circular waveguides

The excitation of very high-order modes in circular waveguides has been performed in a cavity with a connected up-taper with a geometry similar to those used in gyrotrons. A Gaussian beam was coupled to the cavity which was made translucent by an array of holes. With the help of a special optics, the amplitude as well as the phase distribution of the beam was matched to the mode to be excited in the resonant cavity. By simple rotation of one mirror to adjust the phase distribution together with the change of frequency to match the resonance condition, a large number of modes could be produced with one experimental set-up. Field measurements in the output waveguide show a high mode purity of the radiation and confirm the calculations. The method can be used for cold tests of electrodynamic systems operating with these modes, e.g. quasi-optical converters for gyrotrons.     

Design of a low-power tunable quasioptical gyrotron with a slotted output mirror

A low-power tunable quasi-optical gyrotron was designed for driving free electron laser amplifiers in the frequency ránge of 220–270 GHz. The gyrotron cavity consisted of a spherical mirror and a plane slotted mirror to produce a Gaussian radiation output beam. Output powers of 1–10 kW were obtained in the 4 cm length cavity by a few amperes of electron beams with a voltage of 30 kV.     

Output characteristics of right angle cone mirror cavity laser

The anti-misalignment stability and output characteristics of the right angle cone cavity laser are experimentally studied. When the misalignment angle of the cone mirror turns to 46.8 minutes, the single-pulse output energy of the plano-cone cavity laser decreases 24% and the near-field beam patterns have little change; as for the beam directional stability, when the measuring place stands 3.12 m in front of the output mirror, the near-field beam patterns of the plano-cone laser are located at the primary places until the misalignment angle of the cone mirror turns to 18 minutes. These results show that the plano-cone cavity laser has better performances in comparison with the plano-concave cavity laser. The analytical results of the mode instrument are also obtained, which show that the near-field beam intensity distribution of the plano-cone mirror cavity laser is near to the plane wave.     

A High Efficiency Launcher and Mirror System for Use in a 110 GHZ TE22,6 Mode Gyrotron

A four-mirror internal quasi-optical mode converter designed for a CPI gyrotron is discussed. Many improved methods were used in designing the mode converter. The launcher was designed and analyzed using the TOL and Surf3d codes developed by CCR. Mirrors 1 and 2 were designed using analytic surfaces to shape the general wavefront curvature of the beam radiated from the launcher. Mirrors 3 and 4 were iteratively designed using improved techniques that produced smooth mirror surfaces. Good agreement was found between theory and low-power cold-test measurements. The fraction of power coupled between the target Gaussian beam and the output of mirror 4, inferred from measurements, was 0.990. The stray radiation from the internal quasi-optical mode converter, inferred from measurements, was only 1.9% of the total power radiated from the launcher. This resulted in a high overall system efficiency of 97.0%, which is greater than previous designs.     

W波段TE62-TEM00准光模式变换器

对准光模式变换器的基本理论和设计方法进行了讨论.以改进型等效电流理论为基础给出了Vlasov辐射器的分析方法,建立了数值模型,并进行了计算分析.继而推导了自适应相位修正Katsenelenbaum-Semenov算法,编制了相位修正反射镜自适应设计分析程序.在上述理论工作的基础上,针对3 mm波段TE62至TEM00准...     

140 GHz回旋管准光模式变换器的设计（英）

针对一种由Denisov型辐射器和第一面镜为准抛物镜的四级反射镜面系统组成的准光模式变换器开展了详细的研究和设计。利用耦合模理论和矢量绕射理论设计了波纹波导准光模式变化器,通过编写仿真程序进行数值优化完成了140 GHz,TE28,8回旋管准光模式变换器的设计。仿真结果表明,抛物面反射镜的焦距对矢量高斯效率影响较大,输出窗口处得到了较好的高斯波束,标量高斯效率达到98%,矢量高斯效率达到90%。     

94 GHz回旋管准光模式变换器设计

基于几何光学理论和矢量绕射理论,研究了将回旋管及其他高功率微波器件的振荡输出模式转换成准光高斯波束的模式变换器,采用伏拉索夫(Vlasov)辐射器和三级准光反射面实现了准高斯模TEM₀₀的横向输出.研究了Vlasov辐射器的工作机理,运用矢量绕射理论计算出波导辐射场,口面电流分布的方法计算反射面辐射场.通过编写程序设计了将94 GHz,模式为TE₆₂的毫米波转化为准光高斯波束的内置式准光模式变换器. 关键词： 94 GHz回旋管 内置式准光模式变换器 Vlasov辐射器 矢量绕射理论     

Axisymmetric quasi-optical gyrotron oscillator

An axisymmetric quasi-optical gyrotron (ASQUOTRON) is considered to realize a 10 MW, 150 GHz, CW oscillator required for an electron cyclotron resonance heating of a fusion plasma. The gyrotron has an axisymmetric mirror to be used as its optical cavity. It is shown that the axisymmetric mirror of relatively small radius (20 cm) can be used in producing the 10 MW continuous wave with a tolerable mirror heat load (0.5 kW/cm²). Considerations are also made on wave transmissions through the mirror and to a target.     

An improved design for quasi-optical mode conversion of whispering gallery mode gyrotron radiation

Results are reported of a theoretical and experimental investigation of a quasi-optical mode converter for the transformation of whispering gallery mode gyrotron output into a linearly polarized Gaussian like beam. The mode converter consists of a helically cut waveguide launcher, similar to that originally proposed by Vlasovet al, followed by a focusing mirror. Theoretical results using aperture field methods indicate that the length of the waveguide launcher is of critical importance in providing a confined radiation pattern. Experimental results on the radiation pattern were obtained for several launcher lengths using a 0.6 MW, 149 GHz pulsed gyrotron operating in the TE_16,2 mode. Radiation pattern results for the optimum launcher length agree well with theoretical calculations using the Stratton-Chu aperture radiation theory for unperturbed waveguide modes. A mirror focusing in the azimuthal direction was designed by a geometrical optics approach to focus the radiation coming from the launcher. Good focusing with 91.4% efficiency (power in the focused beam divided by gyrotron power) was found experimentally using the combined launcher and mirror with the pulsed gyrotron. These results indicate that quasi-optical antennas are useful for transforming high order, high frequency gyrotron modes into directed beams in free space.     

Design of a Quasi-Optical Mode Converter for a Frequency Step-Tunable Gyrotron

The quasi-optical mode converter for a frequency step-tunable gyrotron which consists of a dimpled-wall antenna (Denisov-type launcher) and a beam-forming mirror system has been optimized for 9 modes from TE_17,6 at 105 GHz to TE_23,8 at 143 GHz. The first mirror is a large quasi-elliptical focusing one; the second and third are phase-correcting mirrors with a non-quadratic shape of the surface. The results of calculations show that for these modes the Denisov-type launcher has a well-focused beam with low diffraction losses, and the radiation pattern presents an almost identical field shape for all modes considered. A multi-mode optimization of the phase-correcting mirrors with two different methods has been tested. The simulations show that the phase-correcting mirrors can be used for broadband operation in the frequency range from 105 GHz up to 143 GHz in the various design modes. This quasi-optical mode converter can achieve efficiencies of 94%-98% for converting the rotating high-order cylindrical cavity modes into the usable fundamental Gaussian mode.     

角隅全反镜谐振腔激光器的输出特性

 在高功率脉冲气体激光器中，用角隅反射镜作为全反镜，平行平面镜作为输出镜构成角隅全反镜谐振腔。对角隅腔激光器的输出特性和抗失调稳定性进行了研究，并与平凹腔和平平腔激光器进行了比较。实验结果表明：在角隅全反镜失调角为16 mrad时，角隅腔激光器的单脉冲输出能量下降9.2%，且近场输出光斑没有明显变化；而凹面全反镜失调角仅为0.4 mrad时，平凹腔激光器输出能量下降了9%，近场输出光斑严重变形。在输出镜正前方3.12 m处测量，当角隅镜偏转16.3 mrad时，激光器输出光斑与标准状态时的输出光斑重合；凹面全反镜失调角为0.4 mrad时，激光器输出光斑位移14 mm。经模式仪分析表明，角隅腔激光器近场光强分布均匀。     

Quansi-optical mode converter for Ka-band application on a gyrotron

A series of electron cyclotron masers (ECMs) has been designed and successfully operated in the frequency range of 6 to 200 GHz over the past 10 years at Strathclyde University. The current Mk. VI ECM operated between 35–200 GHz, the TE _{0 1} ⁰ mode (35.2 GHz) being the lowest order cavity mode excited. Investigation of this ECM and quasi-optical converter combination was made to establish to what extent a Gaussian beam could be produced from the TE _{0 1} ⁰ gyrotron cavity mode.An antenna of the Vlasov (step-cut radiator) configuration was chosen and successfully developed in a series of low-power experiments up to the W-band frequency regime. The low-power experiments demonstrated that such an antenna system could be constructed and operated in the K_a-band frequency region without resorting to high precision quasi-optical components. The final version of the quasi-optical antenna was externally coupled to the output window of the maser and a plane polarized pencil beam was successfully obtained from the combined maser/Vlasov antenna mode converter.A theoretical model involving a single TE _0n ⁰ input mode was chosen to analyse the output beam characteristics from the Vlasov antenna system. Comparison was made between the single mode theoretical model and the experimental results obtained from the maser.     

95 GHz准光模式转换器实验研究

介绍了采用95 GHz准光模式转换器将TE62模式转换为高斯波束的实验测试结果。准光模式转换器由螺旋切口的Vlasov辐射器、一个准抛物柱面反射镜和两个相位修正镜组成。将半径5.62 mm圆波导内的TE62模式转换为束腰直径22.4 mm的高斯波束。实验采用毫米波天线近场扫描测试系统测试,实验结果表明标量转换效率大于97%,矢量转换效率大于88%     

双共焦波导结构二次谐波太赫兹回旋管谐振腔设计

准光共焦波导具有功率容量大、模式密度低的特点,能够有效地减少模式竞争对回旋管互作用的影响,有利于高次谐波太赫兹回旋管的设计.为提高太赫兹准光回旋管的互作用效率,在共焦柱面波导的基础上,研究了一种新型高频互作用结构——双共焦波导结构,设计了一种330 GHz二次谐波双共焦结构回旋管谐振腔并对其进行了理论分析和粒子模拟.研究结果表明,双共焦谐振腔中的高阶模式能够与高次电子回旋谐波发生稳定的相互作用,并且没有模式竞争现象,具备工作在太赫兹波段的潜力.相比普通共焦波导谐振腔,双共焦谐振腔能够增强准光回旋管的注波互作用强度,提高回旋管的输出功率和工作效率.此外,结果还表明双共焦波导中的电磁波模式是一种由两个独立的共焦波导模式叠加而成的混合模式.利用这种混合模式有望实现太赫兹回旋管的单注双频工作,为新型太赫兹辐射源的研究提供了新的途径.     

Asymmetrical mirror optimization for a 140 GHz TE_(22,6) quasi-optical mode converter system

We introduce an asymmetrical mirror design to a 140 GHz TE_(22,6) quasi-optical(QO) mode converter system to correct the asymmetry of the beam's field distribution caused by the Denisov launcher. By such optimization, the output beam with better symmetrical distribution is obtained at the system's output window. Based on the calculated results,the QO mode converter system's performance is already satisfying without iterative phase correction. Scalar and vector correlation coefficients between the output beam and the fundamental Gaussian beam are respectively 98.4% and 93.0%,while the total power transmission efficiency of the converter system is 94.4%. The assistance of optical ray tracing to the design of such QO mode converters is introduced and discussed as well.     

高功率毫米波圆波导半径微扰模式变换器的优化设计

从半径渐变波导的耦合波方程出发,利用龙格-库塔法进行优化数值迭代,得到在3 mm波段,TE03-TE02, TE02-TE01高效率模式变换器的设计参数。通过优化程序,设计出了6周期TE03-TE02和3周期TE02-TE01模式变换器优化尺寸。利用CST微波工作室电磁仿真软件对结构尺寸进行优化仿真,仿真结果与优化程序计算结果基本一致。以此数据设计中心频率94 GHz的TE03-TE02,TE02-TE01模式变换器功率转换效率可以达到98.5%以上,90%功率转换的绝对带宽分别达到3.5和7.0 GHz以上,优于设计要求。     

改进型准光模式辐射器

 应用几何光学理论分析了模式在圆柱波导中的传播,利用耦合波理论分析了各个模式在波纹波导中相互转化以及稳定时的相对功率,设计了170 GHz,模式为TE22,6的毫米波通过波纹波导将其一部分能量转换到其它8个卫星模式上,通过编写程序并进行大量优化得出了耦合出的模式和稳定时的相对功率大小,并使它们各个模式场分布在辐射器螺旋切口上叠加成准高斯波束,设计出辐射器的长度少于150 mm,得到准高斯波束在辐射器螺旋切口上叠加的等势图,实现了直接利用这些准高斯波束的目的。     

Numerical analysis for millimeter wave slot type coupler

The numerical analysis for millimeter wave slot type coupler of overmode waveguide cavity is studied by mode-matching taking account of the thickness of the plate on which the slot is cut. It is found that the higher modes in cavity can be suppressed by proper thickness of the plat and proper dimension of the output waveguide.