Compression of frequency-modulated pulses using helically corrugated waveguides and its potential for generating multigigawatt rf radiation

A new method to generate ultrahigh-power microwave pulses compatible with mildly relativistic electron sources is proposed. This method involves a novel microwave compressor in the form of a metal helically corrugated waveguide, which can enhance the power of frequency-modulated nanosecond pulses up to the multigigawatt level. The results of the proof-of-principle experiments at kilowatt power levels are in good agreement with theory.     

内开槽螺纹回旋行波管线性理论研究

基于耦合波理论，运用阻抗微扰法得到了内开槽螺纹波导的色散方程及耦合条件，并从相对论电子运动方程入手得到了自洽非线性方程组，通过一阶线性近似导出了注-波互作用线性关系及色散方程.运用数值计算及3维粒子模拟软件冷腔分析对该波导冷腔色散特性及注-波互作用色散特性进行了研究. 关键词： 内开槽螺纹波导 阻抗微扰 线性理论 自洽非线性方程组     

螺旋波导压缩频率调制脉冲的初步研究

利用螺旋波导对频率调制脉冲进行压缩可大幅度提高脉冲峰值功率。利用所编Matlab程序对螺旋波导的色散特性进行了计算和分析,获得了波纹幅度和纵向周期长度等结构参数对其色散特性的影响规律;给出了脉冲功率压缩比的计算公式,对不同脉宽和频带宽度、不同频率调制形式的微波脉冲通过螺旋波导后的功率压缩比进行了计算和分析。计算表明:脉冲的频率调制形式对功率压缩比影响较大;相同频率调制形式下,脉冲长度越长,工作频带越宽,功率压缩比越高。为了获得尽可能高的功率压缩比,需对脉冲的频率变化方式进行调节,使其与螺旋波导色散特性匹配。同时还需要在高的功率压缩比和高的压缩效率之间做出权衡。计算得到,当注入脉冲的脉宽为40ns、工作频带为8.8~9.5GHz、频率调制形式与螺旋波导色散特性匹配时,功率压缩比达到了15,压缩效率约为40%。     

螺旋波导压缩频率调制脉冲的初步研究

利用螺旋波导对频率调制脉冲进行压缩可大幅度提高脉冲峰值功率。利用所编Matlab程序对螺旋波导的色散特性进行了计算和分析,获得了波纹幅度和纵向周期长度等结构参数对其色散特性的影响规律;给出了脉冲功率压缩比的计算公式,对不同脉宽和频带宽度、不同频率调制形式的微波脉冲通过螺旋波导后的功率压缩比进行了计算和分析。计算表明：脉冲的频率调制形式对功率压缩比影响较大;相同频率调制形式下,脉冲长度越长,工作频带越宽,功率压缩比越高。为了获得尽可能高的功率压缩比,需对脉冲的频率变化方式进行调节,使其与螺旋波导色散特性匹配。同时还需要在高的功率压缩比和高的压缩效率之间做出权衡。计算得到,当注入脉冲的脉宽为40 ns、工作频带为8.8~9.5 GHz、频率调制形式与螺旋波导色散特性匹配时,功率压缩比达到了15,压缩效率约为40%。     

High-gain wide-band gyrotron traveling wave amplifier with a helically corrugated waveguide

First bandwidth measurements of a novel gyrotron amplifier are presented. The coupling between the second harmonic cyclotron mode of a gyrating electron beam and the radiation field occurred in the region of near infinite phase velocity over a broad bandwidth by using a cylindrical waveguide with a helical corrugation on its internal surface. With a beam energy of 185 keV, the amplifier achieved a maximum output power of 1.1 MW, saturated gain of 37 dB, linear gain of 47 dB, saturated bandwidth of 8.4 to 10.4 GHz ( 21% relative bandwidth), and an efficiency of 29%, in good agreement with theory.     

Two-dimensional colloidal crystal corrugated waveguides

We demonstrate, for what is to our knowledge the first time, two-dimensional (2D) corrugated waveguides at optical wavelengths obtained by use of 2D colloidal crystals. We report experimental studies of light coupling into and out of the waveguide structure. The diffracted light shows interesting optical properties that exist only in such 2D grating structures. Field distribution of the fundamental mode in the structure is studied by use of a simplified model in our analysis. Potential applications of this type of structure are discussed.     

螺旋波纹波导被动式脉冲压缩模拟研究

研究了一种基于螺旋波纹波导特殊色散特性对输入微波脉冲进行压缩的新方法。利用3维全电磁粒子模拟软件对X波段螺旋波纹波导进行了建模,模拟分析了该波导的特殊色散特性及提高功率增益的方法,并将已有模型脉冲压缩增益提高了6.65。模拟结果表明:通过优化输入微波的频率调制特性,可以获得更加符合被动式脉冲压缩所需要的调频形式;采用改进后的椭圆波导,可以得到更有利于被动式脉冲压缩的本征模式;通过延长渐变段长度,可以减少规则段和渐变段之间不均匀性造成的微波反射,从而实现更高的脉冲压缩增益。     

螺旋波纹波导被动式脉冲压缩模拟研究

研究了一种基于螺旋波纹波导特殊色散特性对输入微波脉冲进行压缩的新方法。利用3维全电磁粒子模拟软件对X波段螺旋波纹波导进行了建模,模拟分析了该波导的特殊色散特性及提高功率增益的方法,并将已有模型脉冲压缩增益提高了6.65。模拟结果表明：通过优化输入微波的频率调制特性,可以获得更加符合被动式脉冲压缩所需要的调频形式;采用改进后的椭圆波导,可以得到更有利于被动式脉冲压缩的本征模式;通过延长渐变段长度,可以减少规则段和渐变段之间不均匀性造成的微波反射,从而实现更高的脉冲压缩增益。     

基于螺旋波纹波导高增益高效率被动式压缩方法

对一种改进型螺旋波纹波导实现高增益高效率被动式脉冲压缩进行了研究,并利用微扰理论求解出了该波导的损耗特性。结合波导的色散和损耗特性,设计了输入微波的频率调制形式。还对改进型螺旋波纹波导进行了模拟研究,在输入脉冲宽度为66 ns的条件下,得到了半高宽为1.9 ns的压缩脉冲,增益为21.2倍,脉冲宽度比为34.7倍,压缩效率为61%,这表明改进型螺旋波纹波导应用于被动式脉冲压缩具有高效率高增益特性。     

Diffraction characteristics of planar corrugated waveguides

The diffraction efficiency curves are calculated as a function of the angle of incidence for planar waveguides with corrugation on the waveguide-air boundary or on the waveguide-substrate boundary, respectively. It is shown that the reflectance of the system is increased up to 100% because of the excitation of the waveguide mode. A detailed phenomenological study is carried out taking into account the influence of the waveguide thickness and the corrugation depth. Possible applications of these waveguides as a narrow-band reflection filter and selective mirror are discussed.     

Distributed-feedback terahertz quantum-cascade lasers with laterally corrugated metal waveguides

We report the demonstration of distributed-feedback terahertz quantum-cascade lasers based on a first-order grating fabricated via a lateral corrugation in a double-sided metal ridge waveguide. The phase of the facet reflection was precisely set by lithographically defined facets by dry etching. Single-mode emission was observed at low to moderate injection currents, although multimode emission was observed far beyond threshold owing to spatial hole burning. Finite-element simulations were used to calculate the modal and threshold characteristics for these devices, with results in good agreement with experiments.     

Localization properties of eigenstates in waveguides and cavities with corrugated boundaries

In this paper, we investigate the localization properties of eigenstates for the infinite periodic and closed versions of the generalized ripple billiard (exemplifying corrugated waveguides and corrugated cavities, respectively) having Dirichlet and Neumann boundary conditions. In particular, we demonstrate the existence of strongly energy-localized eigenstates that suffer repulsion, in configuration space, from highly corrugated billiard boundaries. Thus, exhibiting the repulsion effect as a universal property present in billiards with corrugated boundaries. We also characterize this repulsion effect (both, in energy and in configuration space) and provide heuristic expressions for the repelled eigenstate profiles in configuration representation.     

Experimental analysis of mode conversion in waveguides with corrugated walls

Institute of Applied Physics, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 10, pp. 1223–1228, October, 1988.     

Elastic wave propagation in sinusoidally corrugated waveguides

The ultrasonic wave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation.     

High-efficiency wideband flat focusing reflector mediated by metasurfaces

We propose to achieve a high-efficiency wideband flat focusing reflector using metasurfaces. To obtain the wide band,the polarization conversion mechanism is introduced into the reflector design, based on the fact that the reflection phases of cross-polarized waves are linear in quite a wide band. This facilitates the design of wideband parabolic reflection phase profile. As an example, we design two reflective focusing metasurfaces with one- and two-dimensional in-plane parabolic reflection phase profiles based on elliptical split ring resonators(ESRRs). Both the simulation and experiment verify the wideband focusing performance in 10.0–22.0 GHz of the flat reflectors. Due to the wide operating band, such reflectors have important application values in communication, detection, measurement, imaging, etc.     

Optimization of frequency-modulated pulse compression in a sectioned waveguide with a helically corrugated surface

A method of considerably elevating (by 20–30 times) the peak power of frequency-modulated microwave pulses by passive compression in a waveguide with a helically corrugated surface used as a dispersive medium is considered. It is shown that the use of a sectioned compression waveguide (i.e., a waveguide consisting of several sections connected to each other with slightly differing parameters) considerably improves precise tuning of the dispersion characteristic of the system to a desired law of frequency modulation of an input pulse. An algorithm for selecting optimal parameters of the sections is developed, and a high efficiency of the method is demonstrated by several examples.     

Wavelength division demultiplexing by photonic crystal waveguides with asymmetric corrugated surfaces

<正>We propose a new type of wavelength division demultiplexer composed of a photonic crystal waveguide with asymmetric corrugated exit surface.The focus displacement for different symmetric corrugated surfaces is relative to the intensity of the excited surface mode.By systematically investigating the effects of the parameters of the corrugated surface on the focus shift,we demonstrate an on-axis focus by a photonic crystal waveguide with an asymmetric corrugated exit surface at a specific wavelength.The precise equivalences of surface modes at each side of the exit surface are broken.Thus,for the light source with other wavelengths,the emerging beams are off-axis focused at different directions,similar to the function of a wavelength division demultiplexer.     

The sharpness-induced mode stopping and spectrum rarefication in waveguides with periodically corrugated walls

Abstract

Starting from the rigorous excitation equation, the propagation of waves through a 2D waveguide with the periodically corrugated finite-length insert is examined in detail. The corrugation profile is chosen to obey the property that its amplitude is small as compared to the waveguide width, whereas the sharpness of the asperities is arbitrarily large. With the aid of the method of mode separation, which was developed earlier for inhomogeneous-in-bulk waveguide systems [Waves Random Media 2000; 10: 395], the corrugated segment of the waveguide is shown to serve as the effective scattering barrier whose width is coincident with the length of the insert and the average height is controlled by the sharpness of boundary asperities. Due to this barrier, the mode spectrum of the waveguide can be substantially rarefied and adjusted so as to reduce the number of extended modes to the value arbitrarily less than that in the absence of corrugation (up to zero), without changing considerably the waveguide average width.     

插入芯体的螺旋型波纹管液氮流动特性仿真研究

液氮在传输管线中的压降特性一直是高温超导电缆低温系统最重要的设计参数之一。以往针对液氮流动阻力的研究大多在直管或环型波纹管方面,主要关注其几何尺寸对压降的影响。然而,实际应用的长距离高温超导电缆更适合应用螺旋型波纹管。本文主要研究螺旋型波纹管插入导体芯后管内液氮的流动特性。通过建立三维数值模型,对螺旋型波纹管中插入直径为5、8 mm的3根或4根螺旋绞织缠绕导体芯时的液氮流动阻力进行对比分析。结果表明,导体芯的粗细、导体芯自身螺旋缠绕的节距、及导体芯缠绕时相互间形成的空隙大小均是直接影响液氮流动压降、摩擦因子的关键因素,并获得了液氮摩擦因子与上述参数的定量关系。