Design and numerical simulation of coaxial beam-rotating antennalens

A simple lens concept that transforms the aperture field of a conical horn antenna driven by an azimuthally symmetric mode is presented. It is shown that with the appropriate lens geometry the radiated field of the conical horn will exhibit a boresight null (no lens), a boresight peak with linear polarisation, or a boresight peak with circular polarisation     

Eigenvalue equations of N-parallel graded-index waveguides: WKBanalysis

The eigenvalue equations of N-parallel graded-index waveguides are derived in a recursive form for the first time by using the WKB method and the transfer matrix method. For the derivation, trial solutions are defined which not only converge at turning points but also approximate the conventional WKB solutions. It is confirmed through the computer simulation that the results of the derived WKB eigenvalue equations are in good agreement with those of the finite-difference method in the well-guided regions     

Design and analysis of a coaxial coupler for a 35-GHz gyroklystronamplifier

A single rectangular TE₁₀ feed four-slot coaxial coupler is designed and built for excitation of a TE₀₁₁ cylindrical cavity mode for use in high-power millimeter-wavelength gyroklystron amplifiers. A high degree of mode purity is obtained and matching of the cavity to the input line is studied. A model based on the mode-matching technique and dipole radiators has been formulated to predict operation of this coupler. The resulting numerical code is capable of finding resonant frequency and cavity bandwidth in a small fraction of the time taken by more general finite-difference/finite-element design tools. The model can be extended to self-consistently include an electron beam, and the model is compared to a coupler design based on Hewlett-Packard's High-Frequency Structure Simulator code. The coupler has been successfully used in a high-power gyroklystron-amplifier experiment     

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     

面向卫星通信的内导体非接触同轴接头设计方法

针对无源互调(PIM)严重影响卫星通信系统性能和稳定性问题,提出了一种利用内导体非接触式结构实现低PIM的同轴接头设计方法。设计并实现了2款分别工作在S波段和C波段的内导体非接触式同轴接头：S波段的内导体非接触式同轴接头在2.1~2.7 GHz下实测|S₁₁|<-30 dB,通带内插入损耗小于0.3 dB;C波段的内导体非接触式同轴接头在3.5~4.2 GHz下实测|S₁₁|<-30 dB,通带内插入损耗小于0.2 dB。该改进型同轴接头设计方法为卫星通信系统的微波连接器的设计提供了重要的参考价值和新的研究思路。     

On the characteristic impedance of a coaxial line with elliptic cone outer conductor and angular strip inner conductor

The expressions of the characteristic impedance of a new kinds of transmission lines—elliptic cone coaxial line are derived. The formulas are based on the TEM and the transformation of the sphero-conal coordinate into two dimension plane. Also themethods using the graphical approximation and taking the geometrical average of the upper and lower bounds to the size of the line are put forward to calculate the characteristic impedance — of the elliptic cone coaxial line.     

Comparison of three numerical treatments for the open-ended coaxial line sensor

The open-ended coaxial line sensor is commonly used for non-invasive microwave dielectric measurements. A comparison is made between three mathematical treatments that allow the reflection coefficient of the sensor to be derived from the complex permittivity of the material with which it is in contact. It is shown that the discrepancies between values computed by the three methods are much smaller than the predicted measurement uncertainties. Mappings of permittivity contours onto the complex reflection coefficient plane are shown.<>     

A rigorous analysis of a coaxial to shielded microstrip linetransition

The transition from a coaxial to shielded microstrip line is analyzed by applying a rigorous mode-matching technique. The symmetry axes of the two transmission lines are assumed to be parallel, while the relative position of the coaxial line center conductor with respect to the microstrip line is taken to be arbitrary. The fields inside the shielded microstrip line are expanded in terms of the normal hybrid modes, while in describing the fields inside the coaxial line the transverse electric and magnetic modes are utilized. Both propagating and evanescent modes are taken into account in each transmission line. A modified mode-matching procedure is used on the junction plane of the two transmission lines to formulate the corresponding discontinuity problem. The mode-matching equations are solved by applying projection techniques. Numerical stability and computational efficiency are achieved in determining the scattering parameters of the coaxial to microstrip line transitions. Numerical results are computed and presented for several coaxial-to-microstrip-line transition geometries     

宽带激光熔覆同轴送粉喷嘴的设计与数值模拟

为了设计一种适用于大功率的宽带激光熔覆同轴送粉喷嘴,采用FLUENT软件中的离散相模型,对送粉喷嘴的送粉道在不同倾角和不同出口间隙条件下的粉末汇聚特性和浓度分布特性进行了研究。分析了其它条件不变时,外层保护气流速对粉末汇聚的影响,得到了较优的结构尺寸,并利用设计研制的宽带同轴送粉喷嘴装置,进行了送粉和熔覆实验。结果表明,宽带激光同轴送粉喷嘴的焦点浓度在汇聚中心的径向和轴向都近似服从高斯分布;随着倾角的增大,出口间隙对焦距的影响也越来越大,且出口间隙越小,焦距越大;当倾角为70°; ,出口间隙为3.5mm时粉末汇聚性较好,粉末利用率较高;在其它条件不变时,外层保护气体流速过大或过小均不利于粉末汇聚,当外层保护气体流速略小于载气速率时,送粉喷嘴的粉末汇聚特性最佳。表面熔覆质量达到了预期要求,验证了该结构的合理性。所设计的宽带同轴送粉喷嘴对后续宽带激光熔覆的研究与应用具有重要意义。     

Investigation of a method for numerical solution of nonstationary waveguide equations

Results of numerical time-domain calculation of propagation and transformation of ultrawideband electromagnetic pulses in irregular metal waveguides with a variable section are presented for the example of a coaxial corrugated structure. The calculation is performed with the use of a system of nonstationary waveguide equations. A method for estimation of the computation error is described. The method involves the following components (below, referred to as features): monitoring the energy balance, integral estimation of the error in the calculated field, and estimation of the accuracy of the computational realization of the boundary condition on the boundary of the perfect conductor. With the use of a coaxial corrugated structure as an example, it is shown that, for each of the above features, the application of the proposed polynomial basis in the calculations guarantees an accuracy that substantially exceeds the accuracy of measurements. It is shown that the basis of comparison waveguides provides for highly accurate computations in the rms approximation, in spite of the fact that the application of the third feature is impeded because, for a waveguide with a variable section, the boundary conditions cannot be satisfied on perfectly conducting boundary Γ.     

Full-wave analysis of coaxial mounting structure

An efficient full-wave spectral-domain analysis based on the integral equation method is developed for a coaxial mounting structure of a general form. Using this method, the algorithm for complex input gap impedance of such structures has been derived and the calculated data are presented. The method may be useful for designing active and passive devices mounted in a coaxial line     

Field analysis of new coaxial dielectrometer

A field analysis of a composite sample insertion hole in a coaxial re-entrant cavity is performed via a mode-matching formulation. The formulation and the numerical method are presented, and the numerical results are discussed with attention focused on the hole effects on the dielectric loaded cavity. Based on the analysis, and the structure that allows for the sample insertion holes, a dielectrometer featuring both ease of sample insertion and accuracy in dielectric determinations is obtained. It is demonstrated that solid, liquid, or powdered samples can be readily accommodated and measured, and the dielectric data obtained via two theoretically calculated calibration curves are in good agreement with published data     

同轴送粉喷嘴粉末汇聚特性三维数值模拟

在激光金属直接制造过程中,实际的粉末汇聚不是自由射流,而是受阻射流.为了获得受阻射流工艺参数对粉末汇聚特性的影响规律,提高激光直接制造精度,应用FLUENT软件中的离散相模型模拟了工艺参数对粉末汇聚浓度分布的影响.结果表明:在自由射流时,粉末汇聚浓度随着送粉量的增加而增大,随着载气速度的增大而明显降低,保护气速度的增大...     

平顶高斯光束在失调光学系统中的传输特性

为了研究平顶高斯光束经含失调窄缝光阑的失调光学系统的传输特性,采用广义衍射积分法和用有限个复高斯函数之和来逼近窄缝光阑孔径函数的方法,得出了输出光束场分布的近似解析公式,并针对给定的光学系统和平顶高斯光束进行了分析和数值模拟。结果表明,当光阑半宽度与光束束腰半宽度之比较大时(大于1),光学系统的失调量比光阑的失调量对输出光束特性影响更显著。这一结果对分析平顶高斯光束传输特性是有帮助的。     

Air-gap-based RF coaxial TSV and its characteristic analysis

Many 3D IC applications such as MEMS and RF systems require Through-Silicon Via （TSV） with operations for high-speed vertical communication. In this paper, we introduce a novel air-gap coaxial TSV that is suiTab, for such RF applications. Firstly, the detailed fabrication process is described to explain how to acquire such a structure. Then, an Resistor Inductance Conductance Capacitance （RLGC） model is developed to profile the transverse electromagnetic field effect of the proposed air-gap TSV. The model is further verified by a 3D field solver program through the S-parameter comparison. With reference to the numerically simulated results, this analytical model delivers a maximum deviation of less than 6%0, on the conditions of varying diameters, outer to inner radius ratios, and SU-8 central angles, etc. Taking advantages of scalability of the model, a number of air-gap-based TSV designs are simulated, providing 1.6-4.0 times higher bandwidth than the con- ventional coaxial TSVs and leading to an efficient high frequency vertical RF interconnection solution for 3D ICs.     

Development and numerical solution of integral equations forelectromagnetic scattering from a trough in a ground plane

We develop a set of scalar integral equations that govern the electromagnetic scattering from a two-dimensional (2-D) trough in an infinite perfectly conducting ground plane. We obtain accurate and efficient numerical solution to these equations via the method of moments (MoM). Our numerical implementation compares favorably to popular methods such as the finite element/boundary integral (FE/BI) method, generalized network formulation (GNF), and electric field integral equation (EFIE) techniques     

Enforcing causality in numerical solutions of Maxwell's equations

Maxwell's equations in differential form do not distinguish between advanced and retarded solutions. Unless special precautions are taken, a point-by-point numerical integration, based on a finite-difference analog of Maxwell's equations, will lead to a mixture of advanced and retarded fields, inadmissible on physical grounds. The causality requirement can be satisfied if the Maxwell theory is expressed in integral-equation form, with retardation incorporated in all the integrands. A solution using numerical integration will then be physically acceptable.     

二维轴对称-折叠组合腔CO2激光器近场失调分析

为了研究小角度失调对二维轴对称-折叠组合腔CO2激光器输出光束的近场分布的影响,在利用矩阵理论确定平凹谐振腔和凹-平-凹谐振腔失调后的光轴的基础上,采用光束并和思想,对输出光束进行了理论分析和模拟.取得的数据表明,小角度失调对4cm以内的近场强度影响不大,光强仍具有高斯状分布;对4cm以外的近场强度影响较大,光强分布轮廓发生相应的变形,且随着失调角度变大而变大.研究结果表明,在4cm以内的近场具有实用价值.     

A novel numerical synthetic technique for determination of the TMon dispersion relation in a coaxial corrugated cylindrical waveguide

A novel, highly accurate numerical synthetic technique for determining the complete dispersive characteristics of electromagnetic modes in a spatially periodic structure is presented. The numerical method based on the coupling of the finite difference method in time domain with the discrete fourier transform is applied to calculate the eigenfrequencies and eigenfield distribution of a resonant cavity which is an appropriately shorted periodic slow wave circuit of N periods at both ends. The analytical synthetic technique, which is based on the intrinsic characteristic of spatially periodic structure, is used to derive the complete dispersion relation using the numerically measured resonances. The method was successfully applied for the case of TM_on modes in a coaxial corrugated waveguide and is applicable to slow wave structures of arbitrary geometry.     

Radiation characteristics of the short dielectric rod antenna: A numerical solution

The problem of the dielectric rod antenna is studied numerically. The surface integral equation is used to simulate the problem in its actual form. From the surface currents induced on the antenna surface, the far-field radiation patterns are calculated. Different parameters are considered, such as the extension of the dielectric from the waveguide aperture, the waveguide and the dielectric diameter, the dielectric constant and finally the effect of shaping of the dielectric end. The performance of the antenna as a feed for the reflector antenna is also studied by calculating the gain factor, spillover efficiency and the phase center location of the feed. Some of the results are compared with the available experimental data of Dombek. The agreement is found to be excellent.