Modeling of realistic rectangular /spl mu/-coaxial lines

A comprehensive study of small inhomogeneous multi-layered rectangular coaxial lines (RCLs) with irregular cross sections is presented in this paper. An accurate and efficient quasi-analytical technique based on numerical implementation of simply and doubly connected Schwarz-Christoffel conformal mapping is utilized for modeling. Misaligned and offset layers, under-over cutting due to etching, nonuniform dielectric support, and other nonidealities due to fabrication of RCLs are studied and their effects on characteristic impedance, attenuation, bandwidth, and power-handling capacity are discussed. The validity of obtained results is verified with suitable published data, analytical models, and/or finite-element simulations     

Excitation of dielectric resonator antennas by a waveguide probe: modeling technique and wide-band design

Analysis of a dielectric resonator antenna (DRA) fed by a waveguide probe is presented. The probe is excited by the dominant mode of a waveguide and extends into the DRA through an aperture in the waveguide wall. The DRA has, in general, an arbitrary shape and resides on an infinite ground plane, which coincides with the exterior of the waveguide broad wall. A simple and efficient analysis procedure is implemented where the problem is divided into two parts. In the upper part, the input impedance of the DRA excited by a coaxial probe is obtained with respect to the feeding position on the ground plane independent of the waveguide part. Then the input impedance is transformed to the waveguide part as a concentrated load at the end of the probe connected to the waveguide wall. The effect of the wall thickness is taken into account by modeling the section of the probe passing through the waveguide wall as a coaxial cable transmission line supporting the transverse electromagnetic mode. Thus the DRA input impedance is transferred from the ground plane reference to the waveguide inner wall reference. Results obtained using the method of moments are compared with those obtained using the finite-difference time-domain method and exhibit very good agreement. The procedure is used to achieve a bandwidth of 50% for a stacked DRA excited by a waveguide probe.     

Analysis of hollow conducting waveguides using superquadricfunctions-A unified representation

Waveguides of various geometries have found many applications. The analysis of the wave modes inside these waveguides are usually subject to cross sections of the waveguides and specific, but convenient, coordinate systems have to be chosen in the analysis. In this paper, the boundary geometries of waveguides (which include rectangular, circular, elliptical, triangular, coaxial, etc.) are represented in a unified manner by a superquadric function. In this paper, with the Rayleigh-Ritz method, the wave propagation characteristics in a hollow conducting waveguide of the superquadric cross section are analyzed in a unified manner. From the analysis, it is realized that the superquadric function can be utilized to accurately model the boundary of various waveguide structures through variation of the shape parameters. The comparisons between the analytical and computational results show this method is accurate and efficient     

High-power CO2 laser with coaxial waveguide anddiffusion cooling

A diffusion-cooled CO₂ laser using a coaxial waveguide is analyzed theoretically and experimentally. The resonator used for extracting the laser beam consists of two annular plane mirrors enclosing the two ends of the waveguide. The beam exits through an aperture in one of these annular mirrors. The mirror tilt is shown to provide efficient beam extraction through this aperture. A theoretical resonator model based on the vector modes of propagation in a dielectric coaxial waveguide is presented. Experimental data show the feasibility of coaxial waveguide lasers and their ability to supply beams of high power and quality. Experimental data are discussed with respect to the presented theory     

Coaxial feeds for high aperture efficiency and low spillover of paraboloidal reflector antennas

Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H11modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of100degto160deg. Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.     

Cutoff Frequencies of Eccentric Waveguides

This paper discusses the uniform cylindrical waveguide formed by placing one conductor inside a conducting tube. Because of the complexity of the guide's cross section, the numerical technique of the point-matching method is adopted to solve the boundary-value problem. The formulations are carried out for the case when each of the conductors has an arbitrary cross section and also for the case when one of the conductors has a circular cross section. The coaxial waveguide modes, in which the field components have angular variations, split into odd and even modes when the center conductor begins to shift axis to form the uniform eccentric waveguide. However, only even modes in the eccentric guide correspond to the coaxial modes with no angular variations. The dependence of the cutoff frequency on the eccentricity of the guide is determined numerically for even and odd TE and TM modes. Experimental results verify the theoretical calculations for TE modes.     

Scattering at a nonchiral-chiral interface in a coaxial waveguide

A formally exact full-wave solution is presented for the problem of scattering at a nonchiral-chiral interface in a coaxial waveguide. The field components for the axisymmetric modes in a coaxial chirowaveguide are initially obtained. A new orthogonality relation for the modes is then proposed and used to find expansion coefficients for the electromagnetic fields in the coaxial chirowaveguide. The scattering matrix for the nonchiral-chiral dielectric discontinuity in a coaxial waveguide is finally derived by enforcing the continuity conditions of the tangential field components across the interface. Numerical results for the reflection and transmission coefficients at the nonchiral-chiral interface in a coaxial waveguide are presented     

A Finite Dilyerence Method For The Solution Of Electromagnetic Waveguide Discontinuity Problems

Finite difference method for the numerical solution of electromagnetic waveguide discontinuity problems is presented. The method of boundary relaxation is applied, using finite difference techniques in the nonuniform section of the waveguide and using a modal representation of the field in the uniform sections of the waveguide. To illustrate the process some two-dimensional diffraction problems in an electromagnetic waveguide with rectangular cross section are solved.     

Evanescent-mode ridged waveguide bandpass filters with improvedperformance

New types of evanescent-mode bandpass filters based on the ridged waveguide sections are considered. Insertion of additional inductive strips between the ridge sections enables one to reduce the longitudinal filter size, increase the cross section of the ridged waveguide housing, and achieve a sufficient improvement of stopband characteristics. Results of designing the millimeter-wave filters and comparison with the measured data are presented     

Cold tests of open coaxial resonators in the range 9–17 GHz

A study of selective properties of coaxial open cylindrical resonators have been conducted experimentally and compared with theory. The resonator consists of an inner circular cylinder symmetrically located inside an outer weakly irregular open waveguide. Several fundamental TE modes were identified over the range 9 to 17 GHz through measurements of the resonant frequencies and the associated loaded quality factors. It has been verified that the structure and the number of resonant modes are both strongly dependent on the diameter of the coaxial insert. Such an electrodynamical system proves to be useful in guided wave applications requiring, for example, filters, frequency-tunable resonators and devices for analyzing the modal composition of a signal.     

填充多层介质的共焦椭圆同轴线传播特性

采用在椭圆柱坐标系中分离变量的方法,得到了填充多层介质共焦椭圆同轴线模式特征方程.研究表明:当椭圆退化为圆时,利用角向和径向马修函数的渐进关系,可得到填充多层介质的圆形同轴线的模式特征方程,由此可见,圆形同轴线可看作椭圆形同轴线的特例;当椭圆同轴线内导体半长轴大小为零时,则椭圆同轴线就变成椭圆波导,同样的方法,可得到填充多层介质的椭圆波导模式特征方程.当填充一层介质时,得到了椭圆同轴线和椭圆波导的模式特征方程,结果和相关文献所得结果相同.作为示例,对填充一层介质和两层介质的椭圆同轴线中一些模式色散特性进行了数值计算,分析了椭圆同轴线中介质参数的变化以及椭圆同轴结构的变化等对其传播特性的影响.     

模式传输法计算腔体的RCS

腔体结构可以近似简化为通过接头相连接的多段近似规则波导腔体。波经过规则波导腔体可以用模式传输精确模拟 ,经过不规则过渡连接区的特性可以利用传输线的耦合波方程准确分析。根据微波等效网络原理 ,依次连接各段 ,可以求得不规则腔体结构的电磁散射和雷达散射截面。算例所得结果和其他方法吻合的很好。     

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.     

A measure of coupling efficiency for antenna penetrations

The electromagnetic penetration into a shielded enclosure through an antenna connected to a receiver inside the shield is discussed. Reciprocity is used to relate the far-zone fields to the short circuit current in the transmission line. Using a Norton equivalent circuit, a measure of coupling efficiency is derived, relating the electric field incident on the antenna to the current incident on the receiver. It is shown that the coupling efficiency can be determined from standard electromagnetic measurements. As a first example, an open-ended coaxial waveguide is considered. As a second example, a transmission line connected to a receiver inside the shield and to a center-fed dipole antenna outside the shield is discussed. Numerical results are presented for the dipole for various receiver bandwidths and transmission line characteristics. The results are given both in the frequency domain and in the time domain for a pulse incident field     

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.     

一种基于同轴波导的异向传输线

该文提出了一种基于同轴波导的新型异向传输线,与现有基于微带电路的异向传输线相比,这种结构有更高的工作频率、损耗较低和更大的功率容量;与基于同轴波导和矩形波导的异向传输线相比,其结构更简单容易实现。等效电路与有限元仿真的结果均表明这种结构在特定的频段表现出明显的异向特性。     

Input mismatch of TE11mode coaxial waveguide feeds

The reflection characteristics of the TE11mode in a coaxial waveguide antenna due to mismatch at the radiating aperture are described. Results are presented for conventional coaxial waveguide as well as waveguide whose inner conductor extends beyond the aperture plane. Coaxial wavegulde mismatch is often quite large, particularly for conditions of good pattern symmetry, and some matching is usually required. A broad-band matching technique using annular rings inside the waveguide is described for the case where there is no external conductor. Results presented show excellent agreement between theory and experiment.     

The relationship between dual mode cavity cross-coupling andwaveguide polarizers

Cross-coupling in dual-mode cavity filters may be obtained by introducing an asymmetry within the cavity cross section at an angle of 45° to the two orthogonal modes. This paper presents a novel formula relating the resulting cross coupling coefficient between the orthogonal resonances to the polarization of a waveguide polarizer. Previous theories for such polarizers may then be applied directly to the dual mode filter situation. Formulas enabling the dimensions of the asymmetries for required coupling coefficients are presented for square and circular waveguide cross sections     

Frequency-Saturation Effects in Transferred Electron Oscillators

Frequency-saturation effects have been observed in the mechanical tuning characteristics of transferred electron (Gunn) oscillators operating in conventional waveguide cavities at frequencies from 12 to 40 GHz. Their existence leads to a restriction in oscillator tuning range and enhances frequency switching and hysteresis effects in the oscillators. Investigation of oscillator behavior in coaxial cavities as well as in waveguide cavities of varying height has shown that frequency saturation is caused by a coaxial resonance along the mounting post, which in the limit of fully reduced-height waveguide becomes the resonance of the diode with the encapsulation itself, or by a frequency limitation imposed by the diode thickness and operating voltage. The transverse coaxial resonance will occur in any waveguide size at a frequency near to if not within the band of interest. Simulation of the encapsulated diode by a localized reduction in mounting-post diameter shows that the frequency of transverse resonance can be increased by moving the encapsulation to a central position in the waveguide cross section. It is suggested that this technique and that of using cavities with a local reduction of height will make an important contribution to improving the performance characteristics of waveguide-mounted oscillators.     

Thickness Corrections for Capacitive Obstacles and Strip Conductors

Capacitive thickness corrections are derived exactly for two basic geometries involving pairs of semi-infinite plates. In one arrangement the pair of plates are coplanar, while in the other they are parallel to each other. In each case the total capacitance per unit length between the pair of plates is infinite, but the incremental increase of capacitance when the thickness is increased from zero to a value t is finite. These capacitance increments are evaluated, and it is shown how they may be used as approximate thickness corrections in a great varity of more complicated geometries involving capacitive obstacles in waveguide, coaxial line, and artificial dielectric media. They may also be applied to coupled-strip-line conductors. As examples, the corrections are applied in detail to a waveguide iris, and to three useful coupled-strip-line cross sections.