Mode Coupling in a Partially Filled Plasma Waveguide With a Dielectric Liner

The stimulated Raman scattering of a perturbed TM mode in a dielectric loaded partially filled plasma waveguide is considered. The radiation is the result of the scattering of pump electromagnetic wave, which is an EH waveguide mode, off of a space-charge wave. A nonlinear wave equation for a three-wave interaction is used to investigate the coupling of the space-charge and waveguide modes. Dispersion relations for electromagnetic modes are solved numerically to study the frequency characteristics of the interaction of the EH waveguide modes with the space-charge modes. Formulas for the growth rates of the backscattered wave near the electron cyclotron frequency are derived, and the effect of a dielectric liner on the growth rates is investigated. Numerical studies show that the presence of the dielectric liner has an effect on the phase-matching condition and leads to rather larger growth rates close to electron cyclotron resonance.      

A study of plasma filled parallel plate waveguide with one boundary corrugated

Warm plasma theory is used to investigate the propagation of electromagnetic waves in a plasma filled parallel plate waveguide with one boundary plate corrugated. Dispersion relations for TE- and TM-modes are derived and it is found that the propagation of TE-modes is unaffected by corrugation of one boundary plane while the propagation of TM-modes is affected by it. For TM-modes the wave numberk depends on the frequency ta as well as on the distance through which the wave is propagated.The authors take the opportunity to thank Professor M. L. Ghosh, Department of Mathematics, North Bengal University for suggesting the problem and one of the authors (S. K. Ghosh) wishes to express his thanks to the University of North Bengal for financial support.     

Total Transformation of an Electromagnetic Wave Incident on a Corrugated Boundary between Transparent Dielectrics to a Transmitting Wave of the (-1)st-Order Harmonic

We present the results of a theoretical and experimental study of a new phenomenon of total transformation of an electromagnetic wave incident from a dielectric on a corrugated boundary between two transparent dielectrics to a transmitting wave of the (-1)st-order harmonic propagating in the other dielectric. The theoretical study is based on numerical solution of the full-wave equations for electromagnetic field. The experimental study is made using a Teflon prism with a corrugated surface located in a two-mirror resonator.     

Wave-field formation in a hollow x-ray waveguide

Diffraction and refraction phenomena at the entrance of a hollow x-ray waveguide with weakly absorbing dielectric cladding layers are investigated using two independent approaches: (a) analytical and (b) numerical solutions of the wave equation in the paraxial (parabolic) approximation. It is shown that the wave penetrating through the cladding material substantially modifies the wave field near the waveguide entrance. It results in a significant increase of the total energy flux inside the guiding layer and in additional spatial modulation of the electromagnetic field.     

Simulation of a periodic dielectric corrugation with an equivalent anisotropic layer

A periodic, corrugated, dielectric layer is simulated by an anisotropic dielectric layer of equal thickness. The tensor elements of the equivalent dielectric layer are given in terms of the permittivity of the dielectric material, the period of the surface corrugation, and the width of the corrugations. The validity of this technique is verified by comparing the reflection coefficient of the equivalent layer with that of the corresponding corrugated layer using the moment method. Employing a multiple layer approach, the technique is extended to handle periodic surfaces with arbitrary cross sections which can be used to design millimeter wave dielectric plate polarizers and absorbers.     

Finite element analysis of guided waves in fluid-filled corrugated pipes

Free wave propagation in fluid-filled corrugated pipes is analyzed using finite element methods in combination with a wave-based approach. By combining discretized models with a wave-based approach, complex mechanism of wave motion in the three-dimensional waveguide is fully included. The pipes are treated as waveguides having periodic properties in the direction of wave propagation. The analysis of these guided waves leads to dispersion curves which show the strong frequency-dependency of the different wave modes. The method also allows the inclusion of coupling between fluid-borne and structure-borne wave modes which occur at the acoustic-structure interface. Phase and group velocities of the wave modes are derived in postprocessing steps. Additionally, the energy ratio of the fluid-domain and solid-domain vibrational energies is computed. Finally, linear damping models are included in order to explore wave mode attenuation.     

Dispersion Characteristics of Plasma Mode in Corrugated Plasma Waveguide

The dispersion equation of electromagnetic wave is derived for corrugated waveguide filled with plasma immersed in magnetic field under assumption of small corrugation, the dispersion characteristics of low frequency plasma mode are calculated and analyzed, the dense spectrum of plasma mode is demonstrated.     

Enhanced transmission by a grating composed of left-handed materials

We present a detailed theoretical analysis about the influence of surface polaritons on the transmission properties of electromagnetic waves at the periodically corrugated interface between the vacuum and left-handed material by using nonlinear boundary condition approach. The principle behind this approach is to match the wave fields across the grating interface by using a set of linear wave equation with nonlinear boundary conditions. The resonant transmission of the incident electromagnetic radiation in this structure is feasible within a certain frequency band, where there is a range of frequency over which both the electric permittivity and the magnetic permeability are simultaneously negative. The enhanced transmission is attributed to the coupling of the incident electromagnetic wave with the excited surface polaritons on grating interface. Finally, we present the numerical results illustrating the effect of the structural parameters and angle of incidence on the transmission spectra of a TM polarized electromagnetic wave.     

Multilayer resonances sharpened by grating waveguide resonance

A multilayer planar structure comprising a highly reflective multilayer dielectric mirror and a corrugated waveguide is proposed for use as a narrow passband optical filter. The proposed filter has a much narrower linewidth than a usual Fabry–Perot cavity with two multilayer dielectric mirrors. It is shown that the narrowing of the linewidth is due to the strong spectral dependence of the phase of the wave reflected from the waveguide grating mirror. The shape of the pass band can be made symmetrical by a proper choice of the grating groove profile.     

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。     

电磁波在负折射材料填充的3层平板波导中的传播特性

从电磁场理论出发对负折射材料填充的3层平板波导的传播特性进行研究,并进行了数值计算,分析TE和TM波在平板中传播的性质,得到了电磁波的模式方程,与电磁波在右手材料填充的平板波导中的传播特性做了对比,考察了TE模式的能流密度,进行了归一化计算。结果分析表明：基模、一阶模不存在,且任何模式都存在一个截止厚度,随着厚度的增大,模式数量也增多;在一定的入射频率下,平板薄膜厚度趋向一定数值时,可以同时传播多种模式的波,并且入射波频率越高,波导同时存在多种模式的可能性越大;与右手材料相比,左手材料填充相同尺寸的3层平板波导可以传播更高能量的电磁波,导波效果更好。     

等离子体填充波纹波导中低频模式特性分析

采用等离子体流体模型和线性场理论，导出了在强引导磁场下，一无限薄环形等离子体加载 波纹波导中电磁波传播的色散关系.数值计算并分析了在不同的等离子体填充密度下，低频 等离子体模式的色散特性和行波管的小信号增益.研究发现，低频等离子体模式可与相对论 电子束发生同步互作用使高频信号放大.同时，在无限薄环形等离子体填充条件下，波纹波 导中的低频等离子体模式严格满足Floquet定理所要求的周期性，其上截止频率不再受到等 离子体频率的限制，当密度较大时，等离子体模式还可与TM模式发生耦合. 关键词： 等离子体 波纹波导 色散关系 增益     

Diffraction by a corrugated interface of media: The influence of the corrugation shape and losses in the medium on total transformation regimes

We study regimes of total reflection of a plane wave to the diffraction lobe in the case where the wave is incident on a corrugated metal surface or a corrugated interface of two dielectric media. The purpose is to analyze the influence of both the corrugation shape and losses in the medium on the characteristics of the regimes of total reflection to the diffraction lobe. We consider a number of corrugation profiles differing from the sinusoid by the resonance-region width and the presence of additional elements, namely, (i) the profiles having pair resonance regions with scale of the order of the wavelength, for which qualitatively new diffraction regimes compared with those observed for the sinusoidal interface can be realized due to interaction of waves, and (ii) the profiles comprising small-scale deviations, which can be a model of actual gratings. To study the influence of losses in the problem of scattering from a corrugated interface of dielectrics, the dielectric permittivity is assumed complex. We compare the obtained results with data for a sinusoidal profile and loss-free media. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 5, pp. 391–405, May 2006.     

Corrugated waveguide band edge filters for CMB experiments in the far infrared

Millimetre wave corrugated waveguide-horn structures are used as both single-moded and multi-moded bolometer feeds in a number of cosmic microwave background (CMB) experiments (e.g. PLANCK, Archeops, QUaD). Such horns tend to be employed over a relatively wide bandwidth and for single-moded horns the waveguide acts as the high pass filter. In this paper we report on our investigation on how the waveguide details determine the exact location of the low frequency band edge of such corrugated horns. A sharp step-like band edge, below which there is negligible propagation, is ideally required. Furthermore any leakage below the expected cut-off, possible in corrugated guides, could lead to non-idealised cross-polar effects. Typically deeper corrugations are required in the waveguide filter than at the horn aperture for wide bandwidth operation, thus necessitating a transition section over which the corrugation depth smoothly varies. An electromagnetic mode matching technique and a surface impedance hybrid mode model are used to compute the horn transmission characteristics. We have also undertaken laboratory measurements of the band edge of prototype corrugated horns in order to test the models.     

Corrugated waveguide band edge filters for CMB experiments in the far infrared

Millimetre wave corrugated waveguide-horn structures are used as both single-moded and multi-moded bolometer feeds in a number of cosmic microwave background (CMB) experiments (e.g. PLANCK, Archeops, QUaD). Such horns tend to be employed over a relatively wide bandwidth and for single-moded horns the waveguide acts as the high pass filter. In this paper we report on our investigation on how the waveguide details determine the exact location of the low frequency band edge of such corrugated horns. A sharp step-like band edge, below which there is negligible propagation, is ideally required. Furthermore any leakage below the expected cut-off, possible in corrugated guides, could lead to non-idealised cross-polar effects. Typically deeper corrugations are required in the waveguide filter than at the horn aperture for wide bandwidth operation, thus necessitating a transition section over which the corrugation depth smoothly varies. An electromagnetic mode matching technique and a surface impedance hybrid mode model are used to compute the horn transmission characteristics. We have also undertaken laboratory measurements of the band edge of prototype corrugated horns in order to test the models.     

一种电磁带隙结构的快速分析方法

 使用直接传输方法分析有限周期Mushroom-like 电磁带隙结构的表面波带隙,与无限周期的电磁带隙结构表面波色散能带图相比,该方法能大大缩短分析时间。将电磁带隙结构放置于波导底面,通过计算波导的传输系数,分析了不同波导高度和电磁带隙结构周期数对带隙范围的影响。加工了Mushroom-like电磁带隙结构样品,并使用一对探针耦合的方法测量了电磁带隙结构的TE和TM表面波带隙,实验结果表明使用直接传输方法确定的表面波带隙与测量数据吻合良好,证明了此方法的有效性。     

Ferrite resonance isolators in coaxial line and rectangular and planar waveguides with dielectric

A plane-parallel analog of a coaxial line, and a rectangular and planar waveguide with ferrite and dielectric slabs situated in the E-plane is considered. Transcendental equations for determining the propagation constants of an electromagnetic wave in these systems are obtained. Approximate solutions of these equations are given for small thicknesses of the ferrite plate.Analytical expressions for the isolation ratio in these systems are obtained. It is shown analytically that in all cases the maximum isolation ratio is obtained at the resonance magnetic field. For each system, analytical expressions are derived for the optimum value of ferrite magnetization for which the maximum possible isolation ratio should be observed. The value of the optimum magnetization depends on the frequency, the dielectric constant of the dielectric used and the geometry of the system. The values of maximum possible isolation ratio are the same for all three devices.     

未磁化等离子体介质切连科夫脉塞的线性理论

利用线性自洽场理论，讨论了电子在扰动场作用下的三维扰动．在此基础上，对常用的薄环形相对论电子环束在填充未磁化等离子体的介质筒慢波波导中激励的切连科夫辐射进行了详细的分析，导出了此电子环束与慢波系统中任意波导模互作用的色散方程和波增长率，并对其进行了详细的分析和讨论．分析表明切连科夫辐射是由其波导模与电子注模耦合所致．最后详细计算和分析了等离子体密度对色散特性和波增长率的影响 关键词：     

Free space excitation of novel “Fractional” whispering gallery mode dielectric resonators

Solutions to the main problems that limit the sensitivity of an electron magnetic resonance (EMR) spectrometer on the basis of a whispering gallery mode dielectric resonator (WGMDR) are presented. The electromagnetic losses in the transition regions between the overmoded metallic waveguide, the overmoded dielectric waveguide and the mono-mode dielectric waveguide can be avoided by the free space excitation of the resonator that is proved to be very effective for suitably designed resonators. The EMR measurements on high-dielectric-loss samples can be safely developed employing the novel class of “fractional” WGMDRs, in which the usual traveling wave resonator is modified in a structurally stationary wave resonator. Several peculiarities of a fractional WGMDR, investigated both theoretically and experimentally, evidence the advantages of the application of this class of WGMDRs to EMR spectroscopy.