一种准光模式变换器的设计和实验

准光模式变换器是实现高功率回旋管高效输出的重要部件。该文针对140 GHz, TE_28,8模回旋振荡管研制,开展以Denisov型辐射器和3个准光镜面构成的准光模式变换器设计与实验研究。利用标量衍射法优化辐射器辐射口径处的场分布,其与理想高斯场之间的矢量相关性为96.2%;基于几何光学和高斯波束匹配方法设计了聚焦镜面与波束整形镜面,采用3维全波分析软件Surf3D获得各个镜面上及输出窗处的场分布,对所设计的镜面系统进行了仿真验证,在输出窗处获得了高斯模式含量为96.67%的输出波束,整个模式变换器的功率转换效率为93.98%。以自行研制的TE_28,8模激励器作为准光模式变换器的输入,通过对模式变换器转换性能仿真结果验证,在严格控制加工精度及装配和实验过程的基础上,完成了准光模式变换器转换性能的冷测实验。实验结果表明,设计和实验具有合理的一致性,可以作为准光模式变换器工程应用设计和验证手段。     

W波段准光模式变换器的设计

准光模式变换器是大功率输出回旋管的关键部件.采用高转换效率的准光模式变换器可以横向输出电磁波,增大收集极的尺寸,提高回旋管的输出功率,提高整管效率.该文设计的回旋管内置准光模式变换器由Denisov辐射器天线和四个反射镜组成,输入频率为94GHz,模式为TE_6,2模.采用耦合波理论分析和优化了Denisov辐射器内的场分布,并根据矢量绕射理论编制数值模拟程序计算了各个反射镜上的场分布,其输出功率转换效率达97.2%.利用三维全波仿真软件feko6.0进行对比分析,最后加工所设计的结构并内置于回旋振荡管进行热测实验,结果表明其输出场分布与理论计算结果基本一致.     

回旋管准光辐射器研究与设计

准光辐射器是高功率回旋管准光模式变换器的重要组成部分.采用几何光学理论分析圆波导准光辐射器,根据高斯波束(TEM00模)在辐射器切口处形成的原因,利用耦合波理论设计波纹波导准光辐射器.通过编写程序并进行数值优化完成140 GHz、TE28,8模式回旋管波纹波导准光辐射器的设计,结果表明波纹波导辐射器的总长度仅为205.2 mm,切口长度为47.2 mm,在辐射器螺旋切口Brillouin区内高斯模式标量相关系数大于98%.本文所用的方法也可用于其它频率和模式的回旋管准光辐射器设计.     

W波段回旋管准光模式变换器的研究

该文对W波段TE₆₂模回旋管准光模式变换器的辐射器和镜面系统进行了设计与实验验证。基于耦合模理论,采用两级微扰对辐射器进行了设计,获得了圆波导内壁上的类高斯束斑的场分布;基于惠更斯原理的矢量衍射积分理论,对准光模式变换器的镜面系统进行了优化设计,模拟与计算结果表明准光模式变换器的模式变换效率为92.3%。最后,通过热测实验,验证了输出模式为W波段类高斯模式。     

回旋管准光辐射器研究与设计

准光辐射器是高功率回旋管准光模式变换器的重要组成部分.本文首先采用几何光学理论分析圆波导准光辐射器,然后根据高斯波束(TEM00模)在辐射器切口处形成的原因,采用耦合波理论设计波纹波导准光辐射器.通过编写程序并进行数值优化完成140GHz,TE28,8模式回旋管波纹波导准光辐射器的设计,结果表明波纹波导辐射器的总长度仅为205.2mm,切口长度为47.2mm,在辐射器螺旋切口Brillouin区内高斯模式标量相关系数大于98%.本文所用的方法也可用于其它频率和模式的回旋管准光辐射器设计.     

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.     

Experimental study of a high efficiency quasi-optical mode converter for whispering gallery mode gyrotrons

A mode converter for whispering gallery mode gyrotrons has been designed and experimentally demonstrated. Experiments were performed on a megawatt power level, 3μs pulsed gyrotron operating in the TE_16,2,1 whispering gallery mode at 146 GHz. The gyrotron cavity employs a non-linear uptaper to minimize radial mode conversion. About 99% of the output power is in the TE_16,2 mode. The quasi-optical converter consists of a helically cut Vlasov-type waveguide launcher and a reflector. The doubly curved reflector, designed using geometric optics and vector diffraction theory, was built to focus the full radiation pattern to a small, gaussian-like focal spot. Of the power incident in the TE_16,2 mode, 96% is directed by the launcher and reflector to a gaussian-like focal spot in the far field. Small fractions of other modes were found to form distinct focal spots in the far field. Analysis of the power in the other focal spots allows for a good quantitative measurement of gyrotron output mode content, potentially on a single shot basis.     

A High Efficiency Launcher and Mirror System for Use in a 110 GHZ TE<Subscript>22,6</Subscript> 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.     

A high-efficiency quasi-optical mode converter for a 140-GHz 1-MW CW gyrotron

A highly efficient quasi-optical mode converter system with several novel features has been designed and tested at Forschungszentrum Karlsruhe (FZK). The converter consists of a dimpled-wall waveguide launcher, one quasi-elliptical mirror and two toroidal mirrors. The coupled-mode theory has been used to analyze the operation of the prebunching waveguide launcher; the radiated fields from the cut of the launcher have been calculated by the scalar diffraction integral. Simulation results show that the advanced dimpled-wall launcher generates a well-focused Gaussian radiation pattern with low diffraction losses. In this case, toroidal mirrors are sufficient to obtain a desired output beam pattern. An efficiency of more than 98% has been achieved to convert the rotating TE/sub 28,8/ cavity mode at 140 GHz into a fundamental Gaussian beam. Experimental measurements show close agreement with theoretical predictions.     

Broadband linearly polarized beat-wave TEm1/TE11 mode converters

Broadband linearly polarized waveguide mode converters have been developed to transform the high-order cylindrical TE_m1 output wave from harmonic gyrotron amplifiers into the more useful TE₁₁ fundamental waveguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely proportional to the number of periods. Four-period TE ₃₁/TE₁₁ and TE₄₁/TE₁₁ converters with an azimuthal perturbation of m_c=4 and m_c =5, respectively, have yielded a peak conversion efficiency of 98% with a bandwidth greater than 3% and a one-period beat-wave converter has been designed to yield 12% bandwidth. However, it has been observed in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reduction of the efficiency and bandwidth. A two-period TE₄₁/TE₁₁ converter with 5% bandwidth displayed a 5% frequency shift and a conversion efficiency of only 86%     

Theoretical investigation of an advanced launcher for a 2-MW 170-GHz TE/sub 34,19/ coaxial cavity gyrotron

This paper investigates the antenna waveguide (launcher), the main component of the quasi-optical mode converter of a 2-MW 170-GHz TE/sub 34,19/ coaxial cavity gyrotron, which is under development within the European Union. For coaxial gyrotrons operating in very high-order cavity modes like the TE/sub 34,19/, due to the ratio of the caustic to cavity radius of 0.323, the transformation of the high-order cavity mode into a nearly Gaussian distribution cannot be done as good as for gyrotron modes where the ratio of caustic to cavity radius is approximately 0.5. The simulation results for the TE/sub 34,19/ mode show that the average and peak values of the power density at the edges of the cuts of a conventional dimpled-wall launcher are approximately 32.3 W/cm/sup 2/ and 63.8, respectively, which will produce diffraction losses and reflection of power from the cuts. This paper reports on an advanced launcher for which average and peak values of power density of 1.9 and 5.4 W/cm/sup 2/ at the edges of the cuts are achieved, and a well-focused field at the aperture with a scalar Gaussian mode content of 94.8% is obtained.     

Compact quasi-periodic and aperiodic TE0n modeconverters in overmoded circular waveguides for use with gyrotrons

Designs of compact quasi-periodic and aperiodic TE_0n-TE _0n-1 circular waveguide converters for use with gyrotrons in an electron cyclotron heating (ECH) system are developed by analytically and numerically solving the coupled-mode differential equations. Quasi-periodic mode transducer designs which convert the TE₀₂ mode to the TE₀₁ mode, and in some cases also include a taper (waveguide radius reduction), are developed. A 60-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE₀₂-TE₀₁ mode converter. A 140-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE₀₃-TE₀₂-TE₀₁ mode converter. The resulting designs are highly efficient (conversion efficiencies ⩾99.4%), are shorter, have a broader bandwidth than previous designs, and have a waveguide radius greater than or equal to 1.389 cm over the entire length of the transducer to allow for high-power transmission. Experimental results consistent with theoretical calculations are presented     

96GHz边廊模Denisov辐射器

介绍了采用Denisov辐射器将96 GHz边廊模式信号转换为高斯波束的设计、仿真及测试结果.基于耦合波理论给出Denisov辐射器的设计方法.根据96 GHz TE_(6,2)模式Denisov准光模式转换器结构布局的要求,优化得到Denisov辐射器,输入半径6.4 mm,长52 mm,辐射器切割边缘电流幅值为汇聚中心点的10%,输出准高斯能量转换效率达96.51%.由其组成的准光模式转换器冷测输出高斯波束束腰直径22.4 mm,矢量转换效率大于95%.     

Calculation of Radiation from a Helically Cut Waveguide for a Gyrotron Mode Converter in the Quasi-Optical Approximation

We present results of calculations of the radiation from a helically cut waveguide launcher, a so-called Vlasov launcher, which is commonly used either internal or external to a gyrotron for purposes of mode conversion. A gyrotron internal mode converter consists of such a launcher that radiates the waveguide mode as a nearly Gaussian beam in free space followed by a set of mirrors to focus and direct the radiation. The radiation from the launcher is first calculated using a geometric optics representation of the waveguide mode. Then the radiation is calculated in the quasi-optical limit, including diffraction. These analytic results are compared to a rigorous calculation using the computer code SURF3D, which uses an electric field integral equation (EFIE) approach. Good agreement is obtained between the quasi-optical theory and the SURF3D calculation. The present results provide new insights into the accuracy of the quasi-optical theory and may be useful for the design and improvement of Vlasov-type mode converters.     

Propagation of infrared radiation in hollow microstructuralcylindrical waveguides

Theoretical and numerical results are presented on the propagation of infrared radiation in TE₀₁-, TM₀₁-, and TE₁₁-like modes in an empty cylindrical, gold-coated waveguide of micron dimensions. Low-loss propagation is possible for the TE₀₁-like mode, whose configuration is similar to that of the TE₀₁ mode in a guide with perfectly conducting walls. Propagation is more lossy for the TM₀₁- and TE₁₁-like modes. While for small guide radii these modes resemble the TM₀₁ and TE₁₁ modes in a guide with perfectly conducting walls, they transform into surface waves as the guide radius is increased, with losses that are independent of guide radius     

The design of serpentine-mode converters for high-power microwaveapplications

In this paper, we report the design methodology and numerical results for two mode converters that are suitable for high-power microwave applications. Both converters are designed to operate at 11.424 GHz and utilize periodic serpentine structures to convert between modes with different azimuthal-mode indexes. The first converts about 98.5% of an incident linearly polarized TE₁₂ mode to the TE ₀₁ mode when oriented as an H-plane bend, but has just 1% mode conversion to all modes when oriented as an E-plane bend. The second device converts a linearly polarized TE₁₁ mode to a TM ₀₁ mode with over 99.99% effectiveness. The performance of both devices with respect to parametric variations is detailed. Experimental measurements of the radiation patterns from the TE₁₂ -to-TE₀₁-mode converter are consistent with the theoretical predictions     

A composite optical waveguide-based polarimetric interferometer forchemical and biological sensing applications

A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)₀ and transverse magnetic (TM)₀ modes in a composite optical waveguide (OWG). The composite OWG consists of a single-mode potassium ion-exchanged planar waveguide overlaid with a high-index thin film that has two tapered ends and supports only the TE₀ mode. Applying tapered velocity coupling theory, we found that the TE₀ and TM₀ modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE₀ mode was coupled into the thin film while the TM₀ mode was confined in the potassium ion-exchanged layer. Interference occurs between TE- and TM-polarized output components when a single output beam is passed through a 45°-polarized analyzer. The phase difference φ between both orthogonal output components is very sensitive to the superstrate index n_c in the thin film region. Our experimental results indicate that a slight change of Δn_c=3.71×10^-6 results in the phase-difference variation of Δφ=1° for a 5-mm-long TiO ₂/K⁺ composite OWG with a 34-nm-thick TiO₂ film. Such a simple polarimetric interferometer can be applied to chemical or biological sensors by modifying the upper film surface of the composite OWG with a chemically or biologically active substance     

The hexagonal horn as an efficient Gaussian beam launcher

A new type of feed horn-the hexagonal horn-is proposed and investigated by means of Gaussian-Hermite beam-mode analysis. The electric-field distribution at the horn aperture plane is approximated. The polarization efficiency is 88.66%. The fractional power in the fundamental beam mode is about 85%. The near- and far-field radiation patterns are calculated. The high fractional power in the fundamental beam mode of the horn indicates that it can be used as an efficient Gaussian beam launcher in quasi-optical systems     

Propagation of lower-order modes in a radially anisotropiccylindrical waveguide with liquid crystal cladding

The propagation behavior of the four lower-order modes, HE₁₁ , TE₀₁, TM₀₁, and HE₂₁, in a radially anisotropic cylindrical waveguide with liquid crystal cladding is studied both theoretically and experimentally. The cylindrical waveguide is a doubly-clad fiber with an isotropic core and inner cladding and a radially anisotropic outer cladding made of nematic liquid crystal. Theoretically, the propagation and decay constants for the TE₀₁ and TM₀₁ modes are obtained by solving the wave equations exactly, while those for the HE₁₁ and HE ₂₁ modes are derived using perturbation techniques under the weakly guiding approximation. It is predicted that in such a structure the guided TE₀₁ mode can be separated from the leaky HE₁₁, TM₀₁, and HE₂₁ modes. The theoretical results show good agreement with the experimental observations for a 3 cm long fiber cell with a 5 μm inner cladding radius     

一种适用于波束扫描的宽带低剖面介质谐振器天线

近年来,为解决传统介质谐振器天线（dielectric resonator antenna, DRA）体积庞大等问题,新颖的低剖面DRA如介质贴片天线和平面介质天线被提出并迅速成为研究热点.然而,现有的低剖面DRA设计要么平面尺寸较大（>0.5λ0×0.5λ0）,要么带宽较窄（<10%）,限制了它们的实际应用.文中提出了一种具有小型化平面尺寸的宽带低剖面DRA.本天线采用介质贴片设计,顶部为高介电常数的介质贴片,中间为低介电常数的介质基板,底部为缝隙馈电结构.缝隙馈电结构可激励起介质贴片谐振器的基模TE111和高次模TE131两种工作模式,这两种模式的场分布在贴片边缘部分存在基模场强较弱而高次模场强较强的显著区别.本设计巧妙地利用了该区域的模式场强区别,通过略微增加贴片边缘部分高度来显著影响高次模谐振频率而轻微影响基模谐振频率,从而将高次模TE131的谐振频率迅速下拉并与基模TE111的谐振频率靠近合并,在不增大介质贴片平面尺寸的前提条件下获得宽带工作效果.本天线的三维尺寸为0.35λ0×0.35λ0×0.08λ0 (λ0为中心频率处的空气中波长),线极化实物案例测试结果表...