Improvement in dielectric measurement technique of open-ended coaxial line resonator method

An improvement in the dielectric measurement of the open-ended coaxial line resonator method is reported. The usable frequency range has been substantially extended by considering the end radiation effect. Experimental results are given at X-band. The accuracy is much better than in the earlier reported method.     

Diffraction of a coaxial resonator’s hybrid modes by a transverse slot and a cylindrical dielectric layer

The partial-domain method is applied to theoretically solve the problem of diffraction of a hybrid resonance mode by an inner ring slot and a cylindrical dielectric layer in a coaxial cavity with perfectly conducting walls of a finite thickness. The boundary equations for field amplitudes are solved with the use of Tikhonov’s regularization method, and a stable algorithm of calculation of the complex wave number (i.e., the resonance frequency and Q factor of free field oscillations) is developed. Conditions for the energy balance on the slot in the presence of a resonance are considered. Being independent of the field equations, these conditions complement them.     

A coaxial probe for the control of parameters of a multilayer dielectric: Direct and inverse problems

Diffraction of an electromagnetic wave by an open end of a coaxial line with an infinite flange adjoining a piecewise-uniform plane-layered lossy medium is considered. The direct problem is solved on the basis of admittance and impedance algorithms taking into account losses in the flange and the medium. For an infinite conductivity of the flange, a stationary functional for the input admittance is used to find an explicit solution in the form of an integral; numerical results are obtained. The inverse problem consisting in determination of the layer parameters (thickness, permittivity, and permeability) from known (experimental) values of the magnitude of the reflection coefficient at specified frequencies via minimization of the corresponding residual of the least-squares method is considered. It is proposed to increase the amount of experimental data through performance of measurements for several positions of the sample relative to the flange and for different impedance conditions behind the sample. In order to solve the inverse problem, a perceptron neural network is constructed. This approach reduces the solution time by several orders of magnitude.     

Microwave applicator for tubular dielectric materials

A new corrugated circular waveguide applicator with a nonuniform power-density distribution over the cross-section is described. This type of applicator is suitable for treatment of tubular dielectric materials.     

Microwave imaging for a dielectric cylinder

The problem of reconstructing both the shape and the relative permittivity of a homogeneous dielectric cylinder from the measurement of scattered field is numerically simulated. The Newton-Kantorovitch algorithm and the moment method are used to solve a set of nonlinear integral equations. Numerical results show that, with multiple incident directions, good reconstruction is obtained. This algorithm can be applied at a single frequency without limitation on the value of dielectric constant. The effect of random noise on imaging reconstruction is also investigated     

Input impedance characteristics of coaxial slot antennas forinterstitial microwave hyperthermia

In this paper, a transmission-line type of input impedance model originally developed by King et al. (1983) for the insulated dipole antenna embedded in a homogeneous dissipative medium is extended to the case of insulated coaxial slot antenna. Physical construction of the latter indicates the presence of additional current path(s) inside the feed line, which shall lead to the shortening of its resonance length. This effect is taken into account in the impedance model and verified by experiments. Furthermore, a simple strategy for optimizing the applicator's impedance-matching performance is also described and verified. Excellent agreements observed between theoretical and measured S₁₁ data indicate that these models can be relied upon when designing an efficient applicator for interstitial microwave hyperthermia     

细同轴天线的宽频带技术

运用同轴天线的原理,引入附加阻抗,通过同一传输线变压器的不同阻抗变换作用,改善天线的阻抗特性,展宽细同轴天线的频带,同时使天线尺寸大为减小。     

Analysis of dielectric loaded hybrid mode coaxial horns

This article presents a numerical solution for radiation from a novel coaxial horn with a partial dielectric loading. The horn is represented as a set of three-layer dielectric loaded coaxial waveguide sections. Characteristic equation has been obtained to calculate phase coefficients for hybrid modes in each section. Applying mode matching technique generalised scattering matrices for each junction between the sections have been obtained, besides that power coupling integrals for each of three different type of junctions have been found in closed-form solutions. Cascading these scattering matrices with transmission matrices of each section yields a generalised scattering matrix of the horn. For the given excitation at the throat of the horn, amplitude and phase of eigenmodes at the aperture of the horn have been determined. Finally, Fourier transform integral of the aperture electric field has been applied to solve radiation problem of the horn. Numerical results on propagation and radiation characteristics of the first four hybrid modes of the horn are presented and it is validated that this solution can be successfully used for full-wave electromagnetic analysis and optimisation of multiband dielectric loaded coaxial feeds.     

Effects of mechanical flaws in open-ended coaxial probes for dielectric spectroscopy

A detailed study of dielectric properties of breast tissue in the 0.1 to 20 GHz frequency range currently under way uses open-ended teflon coaxial probes as sensors. This letter quantifies the effects of small mechanical imperfections at the probe aperture on the measured reflection coefficient. The mechanical flaws in the probe can lead to significant errors, thus probes for dielectric spectroscopy of breast tissue have to be carefully manufactured.     

Application of inhomogeneous dielectric loading to coaxial resonators

A technique for improving the Q factor of air-filled coaxial resonators by inhomogeneous dielectric loading is reported.     

介质波导中的高模归并法

以介质波导中的模式匹配法和横向共振技术为基础,发展了一种高模归并法.构造的等效简化网络,既能描述基模的特性,又考虑了高模的影响.与模式匹配法或横向共振技术比较,高模归并法简化了传播参数的计算,其网络模型易于理解和应用.     

Some effects of dielectric loading on periodic slot arrays

The applications of arrays of rectangular slots have been severely limited since their resonant frequency (where unity transmission occurs) and bandwidth change with incident angle. By utilizing a modal analysis solution which includes the effects of dielectric slabs on both sides of the array, we show that these dielectric effects can, with proper design, reduce or eliminate the unwanted changes in resonant frequency and bandwidth. The presence of the dielectric slabs also cause other changes in the transmission curves. Two of these changes are the occurrence of the Wood's anomaly ("blind angle") null at a lower frequency, and additional narrow resonances in the transmission curves. These phenomena are explained by considering the behavior of the Floquet modal impedances in the presence of the dielectric layer.     

Radiation characteristics of dielectric-coated coaxial waveguideperiodic slot with finite and zero thickness

The leaky wave radiated from the dielectric-coated coaxial waveguide periodic slot with finite and zero thickness is investigated theoretically for the infinite and finite periodic structures. For the infinite periodic structure, mode-matching technique and integral equation method are applied to the analysis of finite and zero thickness slot cases, respectively. The integral equations are derived for the finite periodic structure by use of the Fourier transform and mode expansion and simultaneous linear equations are obtained. The effects of the slot thickness, the finite slot number and the dielectric coating are analyzed. Results for finite periodic slots are compared with those of the infinite extent structure and good agreement is found     

改进的同轴线传输/反射法材料电磁参数测试

本文基于传统的同轴线传输/反射法,提出一种改进算法,并在2GHz^18GHz频率下反演计算聚四氟乙烯的电磁参数。首先根据HFSS建立仿真模型,其次运用MATLAB编写算法并不断修改提高精度,最终得到改进的反演算法误差小于5%,证明改进算法的有效性。     

Quick accurate design of a frequency-stabilised coaxial dielectric resonator

A numerical study of a composite dielectric resonator of coaxial type is proposed. It consists in finding a simple equivalent structure on which the influence of electrical and geometrical parameters on frequency are well known. A knowledge of the thermal drifts of these parameters can be used for the design of a temperature-stabilised composite resonator. The validity of the method is tested experimentally.     

双轴同轴型微波介质滤波器的仿真与设计

在介绍双轴同轴型谐振微波介质滤波器结构及工作原理基础上,利用理论公式计算与HFSS10.0三维有限元仿真的混合设计方法,设计了满足性能要求(插入损耗为–3dB以上;–3dB带宽为18MHz以上)的微波介质滤波器。滤波器试样实际测试结果表明,该设计方法正确可行,测试结果与仿真结果有很好的一致性,最终设计出的滤波器插入损耗为–2.83dB,–3dB带宽为35MHz。     

900 MHz独块同轴微波介质滤波器的仿真

采用HFSS软件讨论介质滤波器耦合(包括谐振器间的互耦合以及谐振器与外电路的耦合)性能以及中间谐振器谐振长度与其频率的相互关系,得到滤波器外界品质因数与其输入输出端口大小、滤波器级间耦合系数与其耦合孔直径以及中间谐振器谐振长度与其频率之间相互关系曲线,并以此确定所设计的介质谐振器滤波器结构尺寸。根据讨论结果,最终设计出的滤波器性能指标为:中心频率899.5MHz,带宽14MHz,带内波动0.8dB,通带损耗1.5dB,性能满足移动通讯要求。     

A multipole analysis of a dielectric loaded coaxial rectangularwaveguide

A multipole analysis of a coaxial rectangular waveguide whose inner conductor is circular is made in order to determine the TE and TM modes of the system. The analysis is based on using multipole (dipole, quadrupole etc.) electric and magnetic current sources to generate field solutions in the waveguide. These solutions are used to match the electromagnetic boundary condition in a homogeneous coaxial rectangular waveguide and to determine the TE and TM eigenvalues of the waveguide system. Eigenvalue results are compared with results of the generalized spectral domain method and to eigenvalue results for a ridged waveguide. Propagation in a coaxial rectangular waveguide is also studied when the coaxial rectangular waveguide is loaded with lossy inhomogeneous dielectric material. A variational formula is used to relate the TEM, TE, and TM modes of an empty coaxial rectangular waveguide to the propagation in the loaded inhomogeneous dielectric waveguide     

Measurement for dielectric properties of organic liquids at 890 GHz

An automatic measurement system using two-beam interferometer has been used to measure dielectric properties of organic liquids at 890 GHz. The sample cell with fixed length and plane parallel windows was adopted. The influence of phase-shift and absorption coefficient causing by multiple reflection was eliminated by theory. The measuring results of refractive index and absorption coefficient of some kinds of organic liquid are given.     

Pressure dependence of electroluminescence in dielectric liquids

The intensity of electroluminescence has been found to increase for benzene and to decrease for n-hexane, cyclohexane, chloroform, and n-hexane mixed with ethyl alcohol, with increasing hydrostatic pressure. No electroluminescence has been observed in carbon tetrachloride at fields up to the value close to breakdown strength. The results are briefly discussed in terms of electrohydro-dynamic motion and impact excitation of molecules.