TE11mode excitation of flanged circular coaxial waveguides with an extended center conductor

Properties of circular coaxial Waveguide antennas terminated in a plane conductor are analyzed where in the most general case the center conductor is of infinite extent. Solutions for mutual admittance and radiated fields are detailed for all asymmetric modes. An asymptotic solution is also derived for the far-zone fields. We describe results forTE_{11}mode excitation of coaxial waveguides where 1) outside the aperture the conductor is absent, and 2) the center conductor extends to infinity. These antennas are of practical interest as feeds for reflectors. Experimental results are described for several examples and excellent agreement with theory is shown. Comparison of the two cases shows that in 1) there is always an optimum frequency for good pattern symmetry and low cross polarization. The mismatch in case 2) is less than in 1) but pattern symmetry is poor if the ratio of inner to outer conductor radius is greater than about 0.2. Further, in 2) mutual coupling to adjacent annular rings is stronger and the principal plane radiation patterns has widely spaced phase centers.     

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     

Radiation from a dielectric coated hemispherical conductor fed by acoaxial transmission line

A dielectric-coated hemispherical conductor mounted on an infinite perfectly conducting ground plane and fed by a coaxial transmission line is investigated. Green's functions for the region above the ground line are derived with separated homogeneous and particular solution parts so as to be compatible with numerical analysis techniques. A magnetic field integral equation is constructed in terms of the unknown annular aperture tangential electric field and is solved by the method of moments. A comparison of the characteristics of the dielectric-coated hemispherical conductor and a flush-mounted coaxial line to an infinite homogeneous region above the ground plane is presented with respected to the tangential aperture electric field, with respect to the tangential aperture electric field, the coaxial line apparent input impedance, and the far radiated field     

Propagation of short pulses in irregular electromagnetic waveguides with a variable topology of the cross section

A method for real-time electrodynamic calculation of the dynamics of propagation and transformation of short ultrawideband electromagnetic pulses (UWB EMP) in irregular waveguides with discontinuous junctions is presented. The results of numerical simulation of a pulse passing through a junction of a coaxial waveguide having doubly connected cross sections and a waveguide horn with singly connected cross sections and through a discontinuity of the inner conductor in an irregular coaxial waveguide are presented.     

三角形栅格矩形径向线螺旋阵列天线的设计

为了提高矩形径向线螺旋阵列天线的极化和匹配性能,将顺序旋转相位技术应用于天线的设计中,提出了一种12单元三角形栅格矩形径向线螺旋阵列天线(子阵).螺旋天线作为单元天线.设计结果表明:天线具有较高的口径效率和良好的匹配特性,能在一定频带内实现微波的圆极化定向辐射,将多个子阵组合就可以构成高增益的大型阵列.同时,通过对子阵的特殊设计,使其具有较高的功率容量,为高功率微波的定向辐射提供了新的技术手段.     

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.     

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.     

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.     

Analysis of coaxial-line/rectangular waveguide junction with dielectrically sheathed probe

The analysis of a coaxial line/rectangular waveguide junction is presented for the case where the centre conductor is sheathed in a dielectric. Expressions for the current distribution and the admittance of the junction are presented. A comparison of theoretical and experimental results show the theory to be very accurate.<>     

The transient response of the coaxial cone antenna

A coaxial cone antenna whose aperture is in the plane of a ground plane has been described theoretically and experimentally in the time domain. Its response to an incident step along the ground plane is essentially a pulse whose width is equal to the diameter of the outer conductor at the aperture. Limitations on the cone dimensions are also discussed.     

The Propagation Constants of Higher-Order Modes in Coaxial Waveguides With Finite Conductivity

Overmoded coaxial waveguides have been used in coaxial gyrotrons as a key interaction structure. To achieve the required mode selectivity, the resistivity of the center conductor is properly chosen to damp unwanted modes. Considering attenuation due to conductor loss, this study employs the perturbational method to determine the propagation constants of higher-order modes in the coaxial waveguide. The validity of the theoretical model is confirmed by comparison with results obtained using the high-frequency structure simulator (HFSS). Moreover, the method proposed herein is applied to analyze the ohmic mode selection of the coaxial waveguide.     

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     

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.     

A new technique for the quasi-TEM analysis of conductor-backedcoplanar waveguide structures

Numerically efficient and accurate formulae based on the spectral domain method for the analysis of conductor backed coplanar waveguide structures are presented. Quasi-TEM parameters are obtained for these waveguide structures by using piecewise linear functions to approximate the potential distribution at the air-dielectric interface. Techniques such as nonuniform discretization and bound estimation are described which demonstrate shorter computational times. Results on the characteristic impedance calculation of standard coplanar waveguide are given to demonstrate the numerical accuracy and efficiency of the method presented here     

Scattering and transmission matrix representations of multiguidejunctions

The scattering and transmission matrix representations of the mode-matching technique are generalized for multiguide junctions with arbitrarily shaped coupling apertures. A comparison between both representations is given with respect to the CPU time. The relative convergence phenomenon arising in cascaded discontinuities of multiguide junctions is investigated. A numerical criterion for choosing the correct mode ratio among the guides is presented. Also studied is the application to a kind of multiguide junction between a circular waveguide and a coaxial waveguide with hollow inner conductor     

On Solving TM0n Modal Excitation in a Ka-Band Overmoded Circular Waveguide by the Conservation of Complex Power Technique

To measure the radiation properties of relativistic diffraction generator (RDG) in Ka-band, a TM0n modal excitation model is established, which consists of an overmoded circular waveguide and a coaxial line feeding probe. Using the transverse E-field mode matching and the conservation of complex power technique (CCPT), we deduce the scattering matrix at coaxial line to coaxial line and coaxial line to circular waveguide junctions. Then using the overall cascaded junction scattering matrix, the numerical results for the reflection coefficient of the coaxial line and the power distribution of TM0n multi-modal are presented. The numerical results are in agreement with HFSS simulation results and experimental results. The analysis shows that by choosing the appropriate position of coaxial line probe, the power proportion of the device operating mode excited in circular waveguide could be the largest.     

On Solving TM0n Modal Excitation in a Ka-Band Overmoded Circular Waveguide by the Conservation of Complex Power Technique

To measure the radiation properties of relativistic diffraction generator (RDG) in Ka-band, a TM0n modal excitation model is established, which consists of an overmoded circular waveguide and a coaxial line feeding probe. Using the transverse E-field mode matching and the conservation of complex power technique (CCPT), we deduce the scattering matrix at coaxial line to coaxial line and coaxial line to circular waveguide junctions. Then using the overall cascaded junction scattering matrix, the numerical results for the reflection coefficient of the coaxial line and the power distribution of TM0n multi-modal are presented. The numerical results are in agreement with HFSS simulation results and experimental results. The analysis shows that by choosing the appropriate position of coaxial line probe, the power proportion of the device operating mode excited in circular waveguide could be the largest.     

Radial Line Band Rejection Filters in Coaxial Waveguides

A coaxial waveguide with a cylindrical cavity forming a double discontinuity in the outer conductor is known to serve as a band rejection filter in the microwave region. A variational principle is applied to calculate the rejection frequency and a subsequent analysis is conducted to determine the dependence of that frequency on various parameters of the structure. Results are presented graphically and by simple analytical formulas. They demonstrate a newly discovered relationship between the rejection frequency and the width of the cavity, and provide design information which enables prediction of the rejection frequency within a 1 percent accuracy.     

Compact Waveguide-Based Power Divider Feeding Independently Any Number of Coaxial Lines

The device described in this paper has been designed to enable the feeding of many individual plasma sources from a single microwave generator, providing a noninterfering and constant supply of power to each coaxial line driving these plasma sources. The power coming from the generator flows through a waveguide under standing-wave conditions provided by the presence of a conducting plane located at the waveguide end opposite that linked to the generator. Power is extracted from the waveguide, at the maximum of intensity of the E-field standing wave, by a waveguide-to-coaxial-line transition designated as a probe. One or two probes can be set at each such maximum of field intensity (and this on both sides of the waveguide wide wall), yielding a compact power divider. Each coaxial line feeds a microwave field applicator, sustaining plasma, through a matching circuit comprising a tuning means and a ferrite isolator (circulator with a matched load), the latter ensuring that whatever happens to the plasma source, the other feeding lines are not affected. The conditions required for a perfect match of the microwave generator to the power divider are elaborated and examples of actual designs are presented     

On the Pulse Response of a Flush-Mounted Coaxial Aperture

The radiation field pattern of a flush-mounted coaxial aperture is derived in the frequency domain. By using the Lorentz reciprocity theorem, the equivalent current generator is obtained which drives the apparent annular antenna admittance in shunt with the load admittance. The current source, aperture admittance, and load admittance determine the transfer function. The transfer function multiplied by the expression for the spectrum of the incident pulse forms the integrand of the Fourier transform from which the time history of the current waveform in the load admittance may be obtained using a computer. There are several applications of the theory. The one of dominant interest at present may be described as follows. A coaxial transmission line terminated in a known load admittance is located in the interior of a missile. The free end of the cable forms an aperture antenna at the skin of the missile, i.e., at the normal junction of coaxial connectors. The problem is to determine the time history of the current in the load admittance when an intense transient electromagnetic field impinges on the receiving antenna. Very accurate numerical results may be obtained from this theory provided the ground plane is sufficiently large and certain dimensional limitations on the sizes of the inner conductor and sheath of the coaxial aperture (expressed in terms of the wavelength) are met.