The measurement of the phase constant of EH11 mode in the hollow dielectric waveguides

In this paper, we presented the results of experiments of propagation phase shift in the hollow dielectric waveguides of the radius a20 with farinfrared laser (wave length =0.337mm). The experimental results agree well with theoretical expecting values. The results also show that it is to exist a coupling length between TEM_oo mode and the funtamental hybrid waveguide EH₁₁ mode. The coupling length is obtained from our measurement.     

X波段高功率微波TE11模圆极化器

 基于圆波导TE₁₁模的模式简并特性和微波在椭圆波导中传输两个正交TE11模式相速不同的性质,研制了一种带有椭圆波导结构的圆波导TE₁₁模圆极化器。该圆极化器通过圆波导到椭圆波导的过渡段,将输入的线极化TE₁₁模式分成两个等幅、正交的TE₁₁模,然后调整椭圆波导长度,使得两个正交的TE₁₁模式的相位差为90°,实现了TE₁₁模式微波线极化到圆极化的转换。利用时域有限差分软件优化设计了该圆极化器,并按照优化的结构尺寸加工了一套实验装置进行了实验测试,测试结果表明：在工作频率9～10 GHz范围内,该圆极化器轴比小于1 dB,驻波比小于1.1,且功率容量大于1.6 GW。     

A DC excited waveguide multibeam CO2 laser using high frequency pre-ionization technique

High power industrial multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes sharing a common plane parallel resonator. Every discharge tube forms an independent resonator. When discharge tubes of smaller diameter are used and the Fresnel numberN ≪ 1 for all resonators, they operate in waveguide mode. Waveguide modes have excellent discrimination of higher order modes. A DC excited waveguide multibeam CO₂ laser is reported having six glass discharge tubes. Simultaneous excitation of DC discharge in all sections is achieved by producing pre-ionization using an auxiliary high frequency pulsed discharge along with its other advantages. Maximum 170 W output power is obtained with all beams operating in EH₁₁ waveguide mode. The specific power of 28 W/m is much higher as compared to similar AC excited waveguide multibeam CO₂ lasers. Theoretical analysis shows that all resonators of this laser will support only EH₁₁ mode. This laser is successfully used for woodcutting     

Angular spectrum theory to calculate coupling efficiency in rectangular waveguide resonators

Coupling efficiency of the rectangular waveguide resonators are discussed in terms of the method of angular spectrum theory. Under the condition given in the paper, the coupling coefficients for the EH₁₁ mode in the rectangular waveguide resonator are presented as a function of mirror curvature and position. It is shown that there exist two special geometries to provide low coupling efficiency. The method can be applied to the other modes.     

非均匀扰动结构TE0n模式变换器研究

本文提出一种半径和周期双重扰动的非均匀圆波导TE_0n模式变换器. 通过耦合波理论(CWT)和数值优化方法对该模式变换器进行研究, 计算结果与电磁仿真软件基本一致. 与传统的均匀结构半径微扰模式变换器比较, 非均匀扰动结构TE_0n模式变换器可以在更少的波纹周期内实现高于均匀结构的模式转换效率, 95%功率转换绝对带宽增加150%, 器件长度减小接近一半. 本文的研究工作为设计轴向尺寸短、工作带宽大、 转换效率高的高功率回旋管外接模式变换器提供了重要参考.     

A waveguide CO2 laser operating in a Gaussian mode: Experimental analysis

An experimental analysis of the dielectric waveguide laser modes has been carried out and it has been shown that the maximum power output is related to the EH₁₁ or TEM₀₀ mode oscillation. Gaussian mode operation is discussed and practical consequences of this type of operation are demonstrated.     

A CW DCN waveguide laser of high volumetric efficiency

This paper describes a CW submillimeter waveguide laser operating on 190 and 195 μm DCN lines with high volumetric efficiency. The laser cavity is a 3.2 cm inner diameter, 70 cm long, Pyrex tube with plane reflectors (one of them is a copper mesh) against its ends. After optimization of various parameters (such as the N₂:CD₄:He gas mixture, the pressure and the discharge current, the wall temperature and the output coupling), this laser, with only 57 cm long active discharge, delivers 8.4 and 7.6 mW on the 190 and 195 μm lines, respectively, for the EH₁₁ mode. This represents volumetric powers of 75 and 65 μW cm^-3. The free space propagation of the EH₁₁ fundamental mode was found to be as for a gaussian beam, and the absorption of the laser beam in the atmosphere was also measured.     

Far Field Calculations and Measurements of an S-Bend Deformed Oversized HE11-Waveguide Antenna

The mode conversion in an s-bend deformed HE₁₁ waveguide is calculated. With the mode mixture at the end of the waveguide, the corresponding far-fields for different waveguide lengths are calculated and compared with measurements. Optimisations of the total waveguide length and diameter are performed.     

Design of CW High-Power Discharge-Pumped DCN Laser

This paper describes a CW sub-millimeter waveguide dischargepumped DCN laser operating on 190 and 195 mu m lines. The laser discharge length is 3 m, and the resonator length is 3.4 m. The resonator cavity consists of a pyrex tube of 54 mm diameter and two plane reflectors against its ends, one is a plane mirror, the other is a metal mesh. After optimization of various parameters, such as the N₂:CD₄:He gas mixture, the pressure and the discharge current, the wall temperature and the output couple, this laser delivers 200 and 220mW on the 190 and 195 mu m lines, respectively, for EH₁₁ mode.     

Hybrid output mirror for optically pumped far infrared lasers

A hybrid metallic mesh multilayer dielectric coating mirror has been developed for use as an output mirror for optically pumped far infrared lasers. The metallic mesh provides a high reflectance in the far infrared while the multilayer dielectric coating is chosen to provide a maximum reflectivity at the pump wavelength (10 μm). This hybrid mirror has increased the output power of a CH₃F waveguide laser at 496 μm by a factor of 350 over that obtained with a hole coupling mirror. In addition, this mirror results in a far infrared output beam which has a minimum angular divergence limited only by the particular oscillating transverse waveguide mode (the EH₁₁ mode for this experiment).     

Theory of a waveguide laser

The role of diffusion of the components of the gas mixture is the generation mechanism of a waveguide CO₂ laser is analyzed. A method is proposed for reducing the multicomponent problem of linear diffusion with dissipation to a one-component problem. The superposition of relaxation modes for a cylindrical waveguide is considered. The diffusion contribution to the loss of electromagnetic energy is estimated for the case of the field hybrid mode EH₁₁ of a dielectric waveguide. The rapid increase in the loss for a SiO₂ waveguide tube and the observation of the filtration properties of the laser in conditions when the diffusion is taken into account are noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 17–21, July, 1975.     

Quasi-optical waveguide-mode converters using a pair of phase correction mirrors

This paper describes a quasi-optical method for the conversion of modes transmitted through highly oversized circular waveguides. A waveguide-mode is radiated once from a waveguide cut in the form of a radiation beam, which is then properly shaped by two curved mirrors and directed back into the waveguide. The curved mirror shapes are iteratively and automatically determined for given propagation distances using the design technique for phase correction mirrors. The proposed method gives favorable results in designing a waveguide expander/reducer, a TE₀₁-TE₀₂ mode converter, and a TE₀₁-HE₁₁ mode converter.     

双微波源共轴辐射馈线结构的设计

设计了一种将两个不同波段微波源输出微波馈向同一个馈源喇叭的双波段馈线结构。该结构不仅对两个微波源输出的TM01模进行了有效的模式转换,而且实现了两个波段的微波共用辐射天线。采用双弯曲圆波导模式转换器实现高频段微波源输出微波的模式转换和轴线的定量平移;采用中间模式为矩形波导TE10模的圆波导TM01模-同轴波导TE11模的模式转换器,实现低频段微波源输出微波的模式转换及与高频段微波源输出微波的共轴输出。数值仿真结果验证了设计思路的正确性。     

Generation of millimeter wave Gaussian beams and their propagation in a dielectric waveguide

Linearly polarized fundamental mode Gaussian beams were generated and coupled to a hollow circular oversized dielectric waveguide by placing the waist of the beam at the guide entrance. The transmission properties of the waveguide were characterized as a function of frequency for a variety of coupling conditions. These conditions included changes in the input beam waist radius, angle of incidence, and displacement perpendicular and parallel to the guide axis. It has been found that: 1.) power transmission is maximized when the waist of the input beam is centered at the guide input, injected normally, and has a radius of 0.43 times the waveguide radius, 2.) power transmission decreases rapidly with increasing angle of incidence and the rate of that loss increases with frequency, 3.) the waveguide preserves the linear polarization of the input beam, 4.) power transmission in the fundamental waveguide mode is not greatly affected by moderate displacements in the input beam position, and 5.) upon exit from the waveguide the launched EH₁₁ mode propagates as a fundamental mode Gaussian beam in the quasi-far field. The results compare favorably to the transmission theory of Belland and Crenn and approximately to the near and far field mode pattern theory of Degnan.     

Rigorous Analysis of the Disk-Loaded Waveguide Slow-Wave Structures

Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). Although TM ₀₁ mode is it's main mode, the asymmetry mode may be excited by slight asymmetry of the structure, misalignment of the beam, or the asymmetry associated with the input or output structure. So research about asymmetry mode of disk-loaded waveguide is necessary. The general dispersion equation and interaction impedance expression of disk-loaded waveguide is obtained with accurate field theory for the first time. Based on these results, a broadband and a narrowband disk-loaded waveguides are designed which can be used in the Ka band HPTWT. Moreover, the theoretical calculated results are compared with the simulated results from the HFSS (High Frequency Structure Simulator) code using finite element method. It is found that frequency domain overlapped by these two modes of the narrowband structure is very narrow, so the HEM ₁₁ mode may be ignored when calculating Beam-wave interaction. In the other hand, the interaction impedance of HEM ₁₁ mode is very low generally.     

HEM11模磁绝缘线振荡器的高频分析

作为小型化和紧凑型的高功率微波源,磁绝缘线振荡器(MILO)在过去十几年里得到了广泛的研究和发展.在大多数研究中,最低的对称模一直被当作器件的主模.然而,由于结构的对称性或者电子发射均匀度不理想等原因,很容易激励起非对称模式.计算了MILO同轴结构中同时包含对称模和非对称模的本征方程.在此基础上,通过对结构的优化设计,提出了一种HEM₁₁模工作的MILO,并开展了原理性实验.在二极管的电压为480kV,电流为39kA条件下得到了功率为1.2GW,脉冲宽度为40ns的微波输出,功率转换 关键词： 磁绝缘线振荡器 高频特性 11模')" href="#">HEM₁₁模 开放腔     

圆波导TM_(01)-矩形波导TE_(10)模式转换器

设计了一种高功率圆波导TM01-矩形波导TE10模式转换器,可以实现圆波导TM01模式与矩形波导TE10模式之间的相互转换。仿真结果表明:中心频率为9.7GHz时该模式转换器转换效率大于99.99%,回波损耗小于-40dB,转换效率大于90%时的带宽大于0.4GHz。调节底面短路圆波导长度可以实现模式转换器在9.2~10.1GHz范围内调谐(模式转换效率大于99%)。在圆波导和耦合段连接处引入倒角可有效降低场强,提高功率容量,注入功率0.7GW,其表面场强小于1 MV/cm。     

对称单负介质包层平面波导的模式特征

系统研究了负μ材料(MNG)作为包层的对称三层平板波导的传输特性. 研究发现,这种波导既支持快波的传播,又支持TE₀,TE₁模式的慢波传输. 其模式特性不同于左手介质波导和传统介质波导,导模存在的模折射率范围要比它们的大. MNG波导的TE₀快波模缺失,且TE_m模(m>1)的传播常数大于TM_m模的传播常数. TE_m模具有双模特征,且与波导的结构参数密切相关,导致波导中的净能流出现负值. 关键词： 单负介质 平板波导 快波与慢波 传播常数     

Modelling of finite-size grating waveguide filters on the basis of a free-space diffraction approach

The field reflection coefficient R of a high strength and short length waveguide grating section is obtained by resorting to a free-space diffraction approach whereby the waveguide grating is excited by means of a virtual high index prism. The effective index of the guided mode, the coupling coefficient between contradirectionally propagating modes of the grating waveguide as well as the modal field are first obtained in the case of an infinite grating by interpreting the results given by an exact diffraction solution by means of a three-wave coupled mode formalism. These results are then introduced in the coupled wave analysis of the structure of finite extent to provide the field at the entrance of the waveguide grating section where the usual overlap integral with the incident field delivers the reflection coefficient. We neglect only the result of radiation mode propagation. This assumption can be made when the grating section is longer than the propagating length of all the leaky modes.