W波段回旋行波管输出结构的优化设计*

在回旋行波管的设计过程中,输出结构性能的高低直接影响到整管增益的高低以及输出功率的大小。采用切比雪夫渐变波导作为耦合输出段,通过对轮廓线的计算程序进行改进,将中心频率作为可变量进行了修正。仿真结果表明,长度为75mm改进后的切比雪夫渐变结构不仅能抑制工作模式向杂模TE02和TE03的耦合,还能有效减少工作模式的反射。在整个工作频段内,杂模TE02和TE03的耦合系数分别低于-33dB和-65dB,TE01模的反射系数低于-20dB,TE01模的传输系数高于-0.01dB。     

Ka波段TE_（01）模回旋速调管带新型渐变段输出腔设计

利用正余弦拟合的方法和半径渐变波导的耦合波理论,设计出一种Ka波段TE01模回旋速调管带该新型渐变段输出腔。通过Matlab数值计算和HFSS仿真优化,研究了该新型渐变段的传输参数、反射参数、对杂模的抑制等性能指标。仿真结果表明：在渐变段长度为80mm、口径由14mm变化到32mm的情况下,在33～35GHz的范围内该新型渐变的传输参数大于-0.016dB,反射参数小于-55dB,对TE02模的耦合为-25dB和对TE03模抑制在-55dB以下;而该输出腔的中心频率为34.075GHz,Q值为109.6,工作模式TE01模式的模式纯度大于0.94。     

高斯光束—光波导的耦合

本文研究了 Si基 Si O2 光波导与高斯光束之间的耦合。用有效折射率法计算了波导 TE模基模的分布 ;实验测试了与光斑直径小于 10 μm的高斯光束的耦合位置允许误差。结果表明归一化耦合比在5 0 %以上时 ,x- y方向的位置误差应该在± 5μm内 ,z方向位置误差在± 2 0 0μm。     

指向耦合器型TE/TM模分离器结构参数优化设计

采用简单的理论模型 ,对折射率呈渐变分布的钛扩散LiNbO3 波导进行结构优化 ,得到模式分离的最佳结构参数 ,用光束传播方法 (BPM法 )设计了有金属覆盖层的指向耦合器型TE/TM模分离器 ,偏振串音分别达到 -2 0 8dB(TE模 )和 - 2 1 3dB(TM模 )。     

光波导耦合的光束传播方法

本文利用光束传播方法和简正模技术来处理两高斯光束之间的耦合,简便而直观地求得光束间的能量耦合和差拍等特性,从而为渐变折射率光波导耦合系统的分析提供了一种新的方法。     

法拉第磁光波导的耦合模分析

利用法拉第磁光效应可以设计光纤磁场传感器。在磁场传感过程中，磁光晶体薄膜波导的TE模和TM模式之间将发生转换，：其转换效率与磁光晶体的法拉第旋转角度和双折射有关。本文建立了磁光波导的耦合模方程，分析了磁光波导中的TE—TM模转换，提出了通过减小线性双折射和增大法拉第旋转角来提高TE—TM模耦合效率的措施，这些措施有利于增大光束TM模的输出功率并提高光纤磁场传感器的灵敏度。     

一种用于谐波倍增回旋放大器的耦合腔互作用电路

该文提出了一种用于回旋管放大器的新型耦合腔互作用电路模型。基于Ansoft HFSS高频计算软件,分析计算了矩形波导TE□10模输入,圆波导TE○01模输出模式转换系数随几何参数和工作频率的变化关系,讨论了结构变化对模式选择和抑制的作用。HFSS的模拟计算结果表明,对TE□10到TE○01转换,TE○01模能够稳定工作,且能量转换效率最大可以大于97%,－3dB带宽最大可以大于327MHz,是谐波倍增回旋行波放大器的一种可选输入耦合结构。     

渐变型太赫兹空芯波导的传输特性

研究了渐变型空芯波导(GTHW)在太赫兹波段的传输特性。基于几何光学方法,仿真分析了波导的输出光束质量和传输损耗特性。相比均匀型空芯波导,当光从渐变型空芯波导的大端传输至小端或沿相反方向传输时,渐变型波导具有特殊性能。当光从波导大端传输至小端,渐变型和均匀型波导具有相似的弯曲附加损耗,并且渐变型波导具有更高的耦合效率,便于与多种光源耦合;当光从波导小端传输至大端,渐变型波导的传输损耗和输出光束发散角更小。仿真了波导弯曲率、光源发散角和波导锥度等参数对传输损耗的影响。采用波长532 nm的半导体激光器作为光源,进行了验证实验。测量数据与仿真结果有很好的一致性。     

介质平面光波导TE0模模场分布的高斯近似

基于介质平面光波导端面无受限衍射场光束的光束传输因子的特点,阐明光波导TE0模模场分布采用高斯分布近似表达的合理性。基于场分布间的匹配效率计算公式,提出采用等效匹配效率方法确定用于高斯近似表达的等效模场半宽度,给出基于光波导芯层半宽度和归一化芯层驻波参量和归一化包层倏逝波参量表达的光波导等效模场半宽度的函数表达式,给出高斯近似分布与光波导本征场分布的匹配效率,阐明采用等效匹配效率方法确定等效模场半宽度的合理性。采用求解方程组的方法,给出基于光波导芯层半宽度和归一化频率表达的光波导等效模场半宽度的拟合函数表达式,并基于拟合引起的误差分析阐明了拟合函数表达式的精确性。     

过模弯曲圆波导模式耦合设计

基于耦合波理论,波导轴线采用常规圆弧弯曲和改进的正弦弯曲结构,对TE01—TM11模式变换器进行全面优化分析,计算中考虑了多模、反向波、金属壁所带来的欧姆损耗以及相位重匹配等因素.以正弦弯曲设计的Ka波段TE01—TM11模式变换器的转换效率达到99%,带宽超过32%,并得出常弯曲结构中波导半径、波导曲率、变换器长度和转换效率之间的关系.     

A new multimode rectangular horn antenna generating a circularly polarized elliptical beam

A multimode circularly polarized rectangular horn antenna generating an elliptical shaped beam is described. This antenna operates in two orthogonal mode sets, namely the TE10+ TE/TM12and TE01+ TE/TM21modes. By virtue of the higher order TE/TM modes, the apertureE-field distribution can be tapered such that the effectiveE-plane far-field beam width is approximately equal to theH-plane beam width of the other orthogonal set of modes, resulting in low off-axis polarization axial ratio. Because of the tapered aperture distribution, the radiation patterns also have low sidelobes. The elliptical cross section beam is a direct result of the rectangular shaped aperture. This antenna, used in conjunction with a spacecraft to illuminate an elliptical zone on the earth surface, offers high edge-of-coverage gain, low sidelobes, low edge-of-coverage (EOC) axial ratio, less RF sensitivity to the space environment, and low cost. The performance of this antenna has been evaluated experimentally.     

Tapered polymer single-mode waveguides for mode transformation

This paper presents a tapered polymer waveguide structure for coupling light between optical waveguides with differing geometries. Optical fibers, lasers, and other photonic integrated circuit components can be coupled with tapered waveguides. The polymer waveguide performs a mode transformation between different mode shapes and sizes. For example, the mode transformation can be from an elliptical laser diode mode to that of a circular optical fiber mode. The input and output of a tapered waveguide structure are analyzed, for the case of laser to fiber coupling, in order to determine the effect of misalignments on the coupling efficiency. Adiabaticity in waveguide propagation is discussed. The fabrication of our polymer waveguides is also described     

一种磁耦合激励的圆极化滤波天线

提出了一种磁耦合激励的圆极化滤波天线。该天线采用磁耦合技术,实现了TEM模到TE10模的小型化转换,再经过矩形到圆波导的过渡,结合圆极化片的调节,获得向自由空间高效率转换的圆极化电磁波。在介质矩形波导中,引入了4个尺寸不同的耦合探针,通过对这些探针尺寸的调节,可以产生谐振和非谐振模式,获得期望的谐振频率、传输零点、滤波极点和谐振器间的耦合系数等,最终实现良好带外抑制的低频滤波天线性能。实测结果充分验证了设计的合理性。该设计思路对其他多级滤波天线也同样具有借鉴意义。     

A novel polarizer based on directional coupler and surface plasmon polaritons

A novel polarizer with a silver nanoribbon added into a traditional waveguide directional coupler is designed to realize the polarized output of TE mode. A high extinction ratio can be obtained because of the selectivity of surface plasmon polaritons （SPPs） on polarization. The effects of the polarizer parameters on coupling efficiency and extinction ratio are discussed. Simulation results indicate that the coupling efficiency for TE mode can reach about 95%, but only 3% for TM mode, with the extinction ratio of TE mode about 15 dB when the light wavelength is 1550 nm, The polarizer may have potential applications in photonic integrated circuits and quantum information technology.     

一种使用TE11为过渡模的TE01-HE11模式变换器设计

基于弯曲圆波导耦合理论和规则圆波导突变结构模式匹配法, 利用MATLAB软件编写的相关数值计算程序得到波导模式转换结构的优化参量, 最终使用CST软件对模型进行了仿真和验证.该系统主要由三部分组成: 一个TE01-TE01的过渡器, TE01-TE11和TE11-HE11的圆波导模式转换器.计算结果表明, 该TE01-HE11模式转换系统在24.13 GHz的频率有5%的带宽、转换效率超过了99%.计算结果、仿真结果和实物冷测结果是一致的.     

Calculation of a Hyperbolic Corrugated Horn Converting the TEM<Subscript>00</Subscript> Mode to the HE<Subscript>11</Subscript> Mode

Corrugated waveguide transmission lines are in use to transmit high power mm-wave radiation from gyrotrons to the plasma for electron cyclotron plasma heating in tokamaks such as ITER. The coupling efficiency of the gyrotron output radiation formed as a quasi-Gaussian beam to the waveguide mode is a critical issue. A hyperbolic corrugated horn serves as a converter of the TEM₀₀ Gaussian mode to the HE₁₁ mode of a corrugated waveguide. We report the design of a hyperbolic horn for application in the ITER transmission line at 170 GHz. The theoretical conversion efficiency of the horn is higher than 0.995.     

Optimized overmoded TE01-to-TM11 mode converters for high-power millimeter wave applications at 70 and 140 GHz

Mode coupling in bent, oversized, smooth-wall circular waveguides was studied by means of numerical integration of coupled-mode differential equations in order to optimize high-power TE01-to-TM11 mode transducers at 70 GHz and 140 GHz. Such mode transformers are used in the mode conversion sequence TEOn to TE01 to TM11 to HE11 for generating the almost perfectly linearly polarized Gaussian-like HE11 mode from circular electric TEOn gyrotron modes. This quasi-optical HE11 hybrid mode is in many respects ideal for electron cyclotron resonance heating (ECRH) of magnetically confined plasmas in thermonuclear fusion research and for other technical applications. Curvature and ellipticity coupling as well as ohmic attenuation of 6 coupled modes (TE01, TM11, TE11, TE12, TE21, TM21) are included in the coupling matrices. Integral expressions were used for deriving the coupling coefficients for arbitrary modes in bent, smooth-wall waveguide. Lowest level of unwanted spurious modes together with highest transmission efficiency (shortest arc length) is achieved with sinusoidal curvature distribution instaed of constant curvature. The calculated conversion efficiencies of 98.0% at 70 GHz and 95.2% at 140 GHz (interior waveguide diameter D=27.8 mm for 200 kW transmission lines) are in excellent agreement with the measured values of (97.6±0.4)% and (95±1)%, respectively.     

High-performance circular TE/sub 01/-mode converter

This study presents the design and cold testing of a Ka-band TE/sub 01/-mode converter. A wave is efficiently converted from the TE/sub 10/ rectangular waveguide mode into the TE/sub 01/ circular waveguide mode. This converter comprises a power-dividing section and a mode-converting section. The field pattern and the working principle of each section are analyzed and discussed. A prototype was built and tested. Back-to-back transmission measurements exhibit excellent agreement to the results of computer simulations. The measured optimum transmissions are 97% with a 1-dB bandwidth of 5.8 GHz centered at 34.0 GHz. The angle-independent transmissions manifest high mode purity and the field pattern is directly demonstrated on a temperature-sensitive liquid-crystal sheet. In addition to exhibiting a high conversion efficiency, high mode purity, and broad bandwidth, this converter is also easy to construct and is structurally simple.