A new approach to estimate complex permittivity of dielectricmaterials at microwave frequencies using waveguide measurements

In this paper, a simple waveguide measurement technique is presented to determine the complex dielectric constant of a dielectric material. The dielectric sample is loaded in a short-circuited rectangular waveguide. Using a network analyzer, the reflection coefficient of the waveguide is measured. Using the finite-element method (FEM) the exact reflection coefficient of this configuration is determined as a function of the dielectric constant. The measured and calculated values of the reflection coefficient are then matched using the Newton-Raphson method to estimate the dielectric constant of a material. A comparison of estimated values of the dielectric constant obtained from simple waveguide modal theory and the FEM approach is presented. Numerical results for dielectric constants of Teflon and Plexiglas measured at the X- and Ku-bands are presented. Numerical inaccuracies in the estimate of the dielectric constant due to: 1) the presence of airgaps between sample and sample holder waveguide surfaces and 2) inaccuracy in the sample dimensions are also discussed     

Propagation Properties of a Modified Slot Surface Plasmonic Waveguide

In this paper, we present a modified slot surface plasmonic waveguide formed by metallic rod, core dielectric layer, and metallic film on the substrate. Using the finite-difference frequency-domain method, modal field distribution are analyzed firstly. Results show that the fundamental mode could be well confined in the space between the metal rod and the metal film. The dependence of modal field distribution, effective index, and propagation length of the fundamental plasmonic mode without gain on dielectric constant of the core layer, geometrical parameters, and working wavelengths are analyzed and discussed. A kind of available gain dielectric medium was used for the core dielectric layer to extend the propagation length. Results show that the propagation length can be extended observably with the help of the gain dielectric medium. Finally, effect of the thickness of the core dielectric layer on modal field distribution, effective index, and propagation length are analyzed and discussed. Since the modal field distribution, effective index, and propagation length can be controlled by adjusting the geometrical parameters, dielectric constant and gain of the core layer and working wavelengths of the waveguide, this kind of surface plasmonic waveguide can be applied to the field of photonic device integration and sensors.      

Modal Inversion in Circular Waveguides---Part II: Application to Latching Nonreciprocal Phasers

The characteristics of the nonreciprocal phase shifter (phaser) configuration, consisting of a circumferentially magnetized circular toroid in circular waveguide, have been investigated theoretically. By suitably filling the toroid center with a material having a high dielectric constant, it is possible to reverse the normal order of the cutoff frequencies of the TE/sub 11/ and the operating TE/sub 01/ modes. The enhanced modal purity resulting from this inversion could yield significant improvements in the performance of practical phasers. The characteristic equation has been derived for the general case of a magnetized toroid in a circular waveguide, with dielectric material in both the central region and external to the toroid. The equation is valid for an arbitrary range of dielectric constants and magnetization. Differential phase shift calculations have been made specifically for operation within the modal inversion window. It is found that adequate differential phase shifts are obtained, even under the restrictions on geometric dimensions and range of dielectric constants imposed by the inversion requirements.     

周期损耗介质加载波导与均匀圆波导间的模式映射

损耗介质环与金属环间隔加载的周期损耗介质波导能够有效地控制各种模式的衰减特性,这对于抑制毫米波回旋行波管放大器的绝对不稳定性和提高其性能具有重要作用.针对应用于Ka波段、TE01模的回旋行波管放大器的周期损耗介质加载圆波导,系统地分析了该周期系统与均匀系统间的模式映射关系.研究表明,当介质层厚度一定时,均匀介质加载波导中的高阶模式可以映射为光滑波导中的低阶模式,且相互映射的模式在中空区域的场型一致.周期系统中的模式表现出复合模式的分布.在一个周期中,介质段和金属段的模式分别映射为均匀介质波导和金属波导中的模式.明确周期介质加载波导系统与均匀波导系统间的模式映射关系是分析发生在这种复杂的互作用回路中的回旋电子脉塞注波互作用的前提,对简化其物理模型具有指导作用.     

Full-wave analysis of a nonradiative dielectric waveguide with apseudochiral Ω-slab

This paper presents a new microwave device - a non-radiative dielectric (NRD) waveguide with a dielectric pseudochiral Ω-slab - the Ω-NRD waveguide. A rigorous full-wave analysis is presented and the modal equations for the longitudinal-section magnetic (LSM) and longitudinal-section electric (LSE) modes are derived. The dispersion curves and operational diagrams for the first hybrid LSM modes are presented. The effect of the pseudochiral Ω-medium is discussed. New interesting modal features are revealed, showing that the propagation characteristics may differ considerably from the common isotropic case     

Rigorous TE solution to the dielectric wedge antenna fed by a slab waveguide

A rigorous TE solution to the dielectric wedge antenna fed by a slab waveguide of the same material is presented. The method of solution involves modeling the wedge as a sequence of step discontinuities and uses an iterative procedure to track forward and backward partial wave fields, expressed as modal expansions, to obtain the rigorous field solution. Radiation patterns of directive gain are presented. All patterns smoothly decrease from a maximum in the endfire direction and exhibit extremely low side lobe levels. Longer length wedges or smaller dielectric constant materials are shown to produce higher directivity and smaller half-power beamwidths. For slender, gradually tapered wedges, the reflection coefficient of the guided (surface) wave at the input to the wedge is very small indicating a low VSWR for tapered dielectric antennas and there appears to be no gain limitation with antenna length for these antennas.     

Frequency-selective transmission by a leaky parallel-plate-like waveguide

The phenomena of high frequency-selective transmission of a plane wave by a dielectric two-dimensional (2-D) periodic waveguide, comprising a uniform dielectric layer sandwiched by two finite thickness 2-D periodic structures served as the waveguide wall is described. This structure is termed a leaky parallel-plate-like waveguide because the waveguide walls are not perfect reflection mirrors. The scattering characteristics and dispersion relation, including the phase and attenuation constants, of the 2-D periodic waveguide are thoroughly analyzed with the modal transmission-line method and Floquet theory. The extraordinary open stopbands caused by the contra-flow coupling between a leaky parallel-plate-like waveguide and the leaky waves, which are generated by 2-D periodic structures (waveguide walls), are displayed in the form of the Brillouin diagram. The phase-match condition is used to verify the resonant coupling between the incident plane wave and the leaky parallel-plate-like waveguide modes. Specifically, the transmission peak frequencies are accurately predicted.     

Anomalous Low-Loss Transmission in a Gas-Confined Dielectric Waveguide for Millimeter and Submillimeter Wavelengths

A novel low-loss (gas-confined) dielectric waveguide for millimeter and submillimeter wavelengths was previously reported by the author. The waveguide consists of a thin dielectric tube separating an internal high-dielectric-constant gas from an external low-dielectric-constant gas. The attenuation constant of this form of waveguide usually increases with increasing tube thickness. The thick tube is indispensable for a mechanically stable waveguide. In this paper, anomalous low-loss transmission characteristics in a gas-confined dielectric waveguide with a thick tube are described. Some condtions are theoretically found where the attenuation constant of the waveguide with a thick tube is extremely low, due to tight field confinement within the internal gas. A qualitative explanation of the operation mechanism is also given.     

Twin Symmetric E-plane Slab Loaded Waveguide Structure for Point Beam Acceleration

Renewed interest regarding the exploitation of dielectric loaded waveguides in high gradient accelerator structures requires a closed form field formulation as cut-off frequencies and optimisation are problematic for numerical methods. In this paper we will present efficient closed form solution for generic slab loaded waveguide boundary value problems. This solution offers flexibility in a sense that it can be further exploited to derive a Green’s function linking transverse field expressions for planar structures. The developed solution is demonstrated for a twin slab E-plane slab loaded structure coupled to a Point source emitter assembly. The emission characteristics of the point source emitter assembly are optimized to generate a high intensity and focused beam to be fed to this E-plane slab loaded waveguide structure for beam acceleration. The field analysis, mode nomenclature, modal hierarchy, modal bandwidth, cut-off plane, impedance plane and dispersion relations for this accelerating structure is included for sake the of completeness.     

High dielectric constant microwave probes for sensing soil moisture

Implantable soil moisture sensors suitable for long-term monitoring of moisture in highway subgrades and for similar applications are needed. Two candidate designs of microwave sensors (operating range 4 to 6 GHz) have been investigated for such applications. One design uses the fringing field of a low-loss dielectric slab waveguide (relative dielectric constant of 25) to obtain good resolution for finely divided soil such as bentonite clay with moisture ranging from 10 to 50 percent by dry weight for effective sample volumes of 20 to 40 cm². The response of the dielectric waveguide sensor has been calculated in terms of the effective dielectric constant of the soil-water mixture. A model based on index of refraction yields an effective dielectric constant in reasonable agreement with experiment when effects of ionic conduction are accounted for. Another sensor design, better adapted for coarse materials, such as crushed limestone aggregate, uses waves launched from a tapered dielectric slab. By using either frequency or spatial averaging methods, the launched wave sensor accommodated aggregate particles passed by a 0.63-cm mesh sieve, and was found to have satisfactory resolution for the range of 0- to 10-percent moisture by dry weight.     

Modal analysis of step discontinuities in graded-index dielectricslab waveguides

The modal solutions of the TE- and TM-modes of an arbitrary graded-index dielectric slab waveguide have been derived by applying the generalized telegraphist's equations to the equivalent inhomogeneous parallel-plate waveguide model with electric or magnetic walls. These modal solutions have been employed in a mode-matching procedure to calculate the transmission properties of step discontinuities in arbitrarily graded-index dielectric slab waveguides such as diffused optical waveguides having exponential, Gaussian and complementary error-function index profiles. For slab waveguides containing an abrupt offset, the radiated power is found to increase smoothly with increasing displacement. Power loss calculations for an abrupt change in diffusion depth for which the dominant mode is in the vicinity of cutoff, exhibit a sharp transition from almost zero loss to nearly total radiation loss     

光控毫米波介质波导衰减器和移相器研究

本文介绍了两种光控介质波导衰减器和移相器.一种是用高阻硅制成的介质波导.计算表明,由于高阻硅中非平衡载流子的扩散长度较长,由光照产生的电子-空穴对将分布在整个介质波导内,因此这种衰减器有较好的线性.另一种是用高阻硅薄片覆盖在陶瓷介质波导上组成的.用带修正的有效介电常数法计算了这种由两层高介电常数材料制成的介质波导的轴向传输常数、衰减常数和相位常数.实验测量了这两种结构的衰减量、相移量,并与理论计算作了比较.     

An evanescent-mode tester for ceramic dielectric substrates

The TE₀₁ mode in a cylindrical waveguide at a frequency below cutoff is used to probe a ceramic dielectric substrate located on the central plane between input and output cooling loops. Maximum transmission occurs at a frequency determined by the waveguide radius, the substrate thickness, and the dielectric constant. The dielectric constant and loss tangent are obtained from the resonant frequency and the absorption bandwidth. The measurement is insensitive to the position of the substrate in the gap between waveguide sections, and no intimate contact is required     

Series solutions to the arbitrary profile 1-D waveguide andquantum-well problems

The 1D waveguide of arbitrary dielectric profile is solved for TE and TM modes by a method based on series solutions. It is a guess-propagate-iterate scheme. The profile is approximated by small segments of either constant or linearly changing dielectric constant. The method is accurate, generally significantly faster than other methods, and can cope with modes near cutoff; and with lossy, or gain-guided modes. Series solutions are also given to solve the 1D Schrodinger equation     

Propagation in Dielectric Slab Loaded Rectangular Waveguide

Propagation in dielectric loaded rectangular waveguide is investigated theoretically for varying slab thickness and dielectric constant. The slabs are placed across the center of the waveguide in the E plane. This geometry is found to offer bandwidths in excess of double that of rectangular waveguide for dielectrics having dielectric constants of approximately 18. Power handling capacities which are double or triple that of standard waveguide are achievable using the dielectric loaded waveguide. In addition to the theory, design curves of bandwidth, guide wavelength, cutoff wavelength, impedance, power handling capacity, wall losses, and dielectric losses are presented and compared to experiment where possible.     

A TE/TM modal solution for rectangular hard waveguides

A TE/TM modal solution for a longitudinally corrugated rectangular waveguide is developed. These longitudinal corrugations can be used to excite a quasi-TEM wave and form a hard waveguide by correctly choosing the impedance at the guide wall. The correctly chosen impedance is referred to as the hard boundary condition. The modal solution developed here solves the problem of longitudinal corrugations filled with a dielectric material by first finding and solving the characteristic equation for a complete TE/TM modal set. It is shown that this TE/TM mode solution can be used to achieve the hard boundary condition resulting in the quasi-TEM wave in a hard waveguide for discrete values of corrugation depth. Beyond each of these depths, a mode becomes a surface wave. The theoretical mode set is amenable to the solution of problems using the mode-matching method. A combination of the mode-matching method and the TE/TM modal solution will allow the solution of larger problems.     

Transverse Modal Analysis of Printed Circuit Transmission Lines

Dispersion characteristics of finned rectangular waveguides, finlines, shielded slotlines, shielded microstrip and striplines, and shielded two-coupled slotlines and striplines are formulated by the transverse modal analysis method. A rectangular cavity is formed by placing two electric walls transverse to a uniform transmission-line system. Considering that the wave propagation is in the direction transverse to the transmission line and to the dielectric discontinuities, the rectangular cavity can be viewed as multiple rectangular waveguide sections joined by the discontinuities. The rectangular waveguide modal analysis technique is readily applicable to obtain the dispersion characteristics by matching the boundary conditions at the discontinuities interface. Numerical solutions are obtained using Galerkin's method, and the results are compared with several numerical techniques for various transmission-line systems.     

Generalized Coupled Dielectric Waveguide and its Variants for Millimeter-Wave Applications

The characteristic equations of hybrid TM and TE modes for a generalized coupled dielectric waveguide are derived using the mode-matching technique. From the characteristic equations of the generalized coupled dieketric waveguide, the phase constant, wave impedance, and field distribution can be evaluated. A variety of single and coupled dielectric waveguides can be obtained by assigning proper parameter values to the generalized coupled dielectric waveguide.     

Electrodynamical Model of Composite Cylindrical Structure with Laminated Dielectric

The article is devoted to the problem of the natural electromagnetic modes, the regions of their existence and the relationship with all possible types of resonances in the waveguide junction of a cylindrical and radial waveguides with a layered (laminated) filling of the radial waveguide with dielectric material. An electrodynamic model is created on the basis of a rigorous method of modal matching technique, with the separation of the common waveguide coupling region and the representation of the field in it in the form of a superposition of the fields of the partial waveguide eigenmodes. The structure under investigation can be used to measure the electrical parameters of dielectric samples of a cylindrical cross-section. It is shown that the measurements will have a local character, since the spectral characteristics of the junctions are determined mainly by the size of the central coupling region of the waveguides and by the electrical parameters of the dielectric that is in the junction. The problem of edge effects for samples of finite length (partial filling of a radial waveguide with dielectric) is investigated. Taking into account the edge effect enables reducing the error in measuring the permittivity for samples of arbitrary sizes in the investigated structure.     

介质片非对称加载矩形波导中的TEM场区

本文证明了具有不同介电常数和厚度的双片介质加载矩形波导中可以存在TEM场区,并导出了介质片厚度与介电常数和工作频率之间应满足的关系,讨论了这种波导的传输特性。