Scattering at an offset circular hole in a rectangular waveguide

A solution is given for the problem of scattering at an offset circular to rectangular junction and at a thick diaphragm, with an offset circular aperture, in a rectangular waveguide. The method used is mode matching for computing one discontinuity. The difficulty arising from the fact that the eigenmodes of the two waveguides are known in different coordinate systems is overcome by simple transformation for the evaluation of overlap integral between the eigenmodes of each waveguide. Experimental results validate this method     

S-matrix of a slot-coupled circular to rectangular waveguide T-junction

An analysis of a slot-coupled T-junction consisting of a circular to rectangular waveguide is presented. The Galerkin method of moments with entire domain sinusoidal basis functions is used to solve the slot aperture electric field integral equations taking into account finite wall thickness. The slot coupler characteristics are deduced, including resonant length and dominant mode scattering. The theoretical results on the magnitude of the s-parameters are compared with experimental results. The effect of the variation of diameter of the circular waveguide as well as the width of the slot on the resonant length of the slot is also studied.     

Mode-matching CAD of rectangular or circular multiaperturenarrow-wall couplers

A rigorous and efficient mode-matching computer-aided design (CAD) method for rectangular waveguide H-plane couplers is presented. The couplers employ multiple large rectangular or circular apertures of different sizes and nonuniform distance. The decomposition of the coupler structure into adequate mode-matching key-building blocks, i.e., the T-junction, double-plane step discontinuity, and rectangular-to-circular waveguide transition, together with the homogeneous intermediate waveguide sections of finite lengths yield the desired high flexibility. Both the finite wall thickness and the higher order mode interaction between all discontinuities are accurately taken into account by the combination of the individual building blocks of the generalized scattering matrix technique. Design examples for rectangular and circular aperture provide coupling values of -10.7, -10, -8.1, -5.3, -4.7, -3, -2.6, and -2.3 dB in Ku-band (12-18 GHz), thus demonstrating the flexibility and the efficiency of the method. The theory is verified by excellent agreement with measurements     

Scattering at Circular-to-Rectangular Waveguide Junctions

A formally exact solution is given for the problem of scattering at a circular-to-rectangular waveguide junction and at a thick diaphragm, with a centered circular aperture, in a rectangular waveguide. The method uses normal TE and TM mode expansions of the waveguide fields and traditional mode matching of the transverse electric and magnetic fields at the junction boundary. Exact closed-form expressions are obtained for the electric field mode-matching coefficients which couple the TE(TM) modes in the rectangular guide to the TE(TM) and TM(TE) modes in the circular guide. Numerical results are presented for the case of TE/sub 10/ mode propagation in the larger rectangular guide with all other modes cutoff. Convergent numerical results for the equivalent shunt susceptances of such junctions are obtained when about 12 modes (eight TE and four TM) are retained in the circular waveguide or in the circular aperture of the diaphragm. The results are graphically compared with formulas and curves due to the quasi-static theory of Bethe and the variational theory given in the Waveguide Handbook [2].     

Galerkin solution for the thin circular iris in aTE11-mode circular waveguide

An integral equation for the transverse electric (TE) field in the aperture of a concentric circular iris in a transverse plane of a circular waveguide is approximately solved using Galerkin's method. The aperture field is represented by a finite sum of normal TE and TM (transverse magnetic) circular waveguide modes that fit the circular aperture. The numerical convergence of the Galerkin solution is demonstrated using the resultant aperture field distributions and equivalent shunt susceptance for the case of dominant TE₁₁-mode excitation. The resultant aperture electric field distribution closely resembles that of the TE₁₁ aperture mode alone, except for edge contribution behavior at the edge of the iris. A resonant or capacitive iris is possible over a restricted range of frequencies     

Harmonic gyrotron interaction in circular and rectangular waveguides

Coupling between waveguide and fast cyclotron modes, as expressed by the interaction impedance, is a function of waveguide geometry and mode, orbit radius, and orbit location within the guide. This paper analytically determines the impedance as a function of these variables in rectangular and circular waveguide. Plots and tables of numerical results are presented, and specific recommendations are made.     

圆形槽波导到矩形波导结的有限元分析

设计基于圆形槽波导的元件经常会用到圆形槽波导到矩形波导结.应用有限元法(FEM)分析了N端口波导结.采用完全匹配层(PML)将槽波导的开放边界截断为有限区域,然后对圆形槽波导到矩形波导结的散射特性进行了数值计算,得出的散射参量为圆形槽波导振荡器输出结构的优化设计提供了依据.     

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     

Experimental investigation of millimeter wave Gunn oscillator circuits in circular waveguides

Millimeter wave Gunn oscillator circuits using circular waveguides for 33–50 GHz and 75–110 GHz frequency bands are described. These oscillators are simpler to construct at millimeter wavelengths compared to the conventional rectangular waveguide circuits. The effect of various circuit parameters on the oscillator frequency and output power has been experimentally studied. The CW power and mechanical tuning range obtained from the circular waveguide Gunn oscillators are found to be comparable and sometimes even better than those obtained with conventional rectangular waveguide circuits using the same Gunn device.     

On the aperture and pattern space factors for rectangular and circular apertures

A consequence of a recently discovered edge condition for planar apertures is that all planar aperture distributions are separable physically into a product of an edge factor and an aperture space factor, analogous to the way in which the radiation pattern separates into a product of an element factor and a pattern space factor. An exact relationship between these aperture and pattern space factors for physically realizable vector fields is derived here for rectangular and for circular apertures. For rectangular apertures it leads to a two-dimensional set of doubly orthogonal functions that are characteristic of the aperture geometry. Characteristic functions for circular apertures, however, are shown to exist only if the vector fields are circularly symmetric, although for scalar fields they exist for completely arbitrary aperture distributions with arbitrary edge taper. For rectangular apertures the characteristic functions consist of products of spheroidal functions and for circular apertures they are obtained from a generalization of the spheroidal functions. Some of the properties of these generalized spheroidal functions are developed here.     

Electric and Magnetic Coupling through Small Apertures in Shield Walls of Any Thickness

A method is presented for evaluating the coupling between two identical resonant cavities coupled by a small aperture in a plane common wall of arbitrary thickness. The coupling is related to the frequencies of the symmetric and asymmetric modes of oscillation of the coupled cavity structure, and a variational technique is used to determine those frequencies. The method is applied to circular and rectangular apertures, and it is shown that the coupling is separable into electric and magnetic terms. The results enable theoretical solutions to be obtained for the electric and magnetic polarizabilities of circular and rectangular apertures in walls of zero thickness, and equivalent polarizabilities to be obtained when the wall thickness is nonzero. Curves of numerical values are given for circular and rectangular apertures. With zero wall thickness, the results obtained are the same as those of Bethe for a circular aperture and give good agreement with Cohn's experimental results for rectangular apertures.     

Radiation pattern synthesis for circular aperture horn antennas

A set of radiation pattern functions, suitable for synthesis of radiation patterns from circular aperture horn antennas, is obtained by assuming an aperture distribution consisting of the fields of cylindrical waveguide modes. A technique is presented for using a linear combination of the radiation pattern functions to approximate a desired radiation pattern. Linear combinations of the radiation pattern functions resulting in maximum secondary gain, when used to illuminate a paraboloidal antenna, are obtained empirically. Using spherical wave theory, maximum performance theoretically obtainable from an antenna is derived as a function of the aperture size of the feed system; the feed efficiency resulting from these theoretical limits on performance is compared to the feed efficiency of patterns obtainable from circular aperture horn antennas, and to experimental results of attempts to realize optimum circular aperture horn patterns.     

The RCS of a cylindrical array antenna coated with a dielectric layer

The scattering properties of dielectric coated waveguide aperture antennas mounted on circular cylinders are investigated. Both the single element antenna and the array case are treated. The array antenna consists of 4 /spl times/ 32 rectangular apertures placed in a rectangular grid on the surface of an infinitely long circular cylinder. The problem is formulated in terms of an integral equation for the aperture fields which is solved with the method of moments using rectangular waveguide modes as basis and test functions. An efficient uniform asymptotic technique is used to calculate the excitation vector and the backscattered far-field. The asymptotic solution is valid for large cylinders coated with thin dielectric layers away from the paraxial (i.e. near axial) region. A similar asymptotic solution is used to calculate the mutual coupling in the nonparaxial region. For the self coupling terms and for the mutual coupling in the paraxial region a planar approximation is used with a corresponding spectral domain technique. Numerical results are presented as a function of frequency, angle of incidence, cylinder radius, and electrical thickness of the coating.     

Silica-based circular cross-sectioned channel waveguides

A technique for fabricating silica channel waveguides with circular cross sections is presented. The geometrical mismatch between a square or rectangular waveguide and a regular optical fiber is therefore largely reduced. The fiber-waveguide-fiber coupling loss drops from 1.8 dB to 0.5 dB or less for step index multimode waveguides by applying this technique. The heat treatment applied in the waveguide rounding process also smooths the waveguide sidewalls and results in much lower propagation loss in the waveguides. Uniform Y splitters were fabricated to show the feasibility of using this technique to make integrated optical devices.<>     

Performance of an array of circular waveguides with strip-loadeddielectric hard walls

An infinite planar periodic antenna array of radiating open-ended circular waveguides is considered. The conducting waveguide walls are covered with dielectric layers loaded with longitudinal conducting strips for providing the hard wall boundary condition. Analysis of the array is carried out by the mode-matching method. The waveguide modes involved in the method are calculated by using the asymptotic strip boundary condition. It is shown that they are split into an independent subsystem of TE modes for the whole cross section and two independent subsystems of TM modes: one is for the central region and another is for the layer region. The calculations show that the operation of the hard waveguides in an array with small element spacing is similar to that of the multimode smooth wall waveguides completely filled with dielectric. For large diameters and element spacing, the hard waveguides have significant advantages over the smooth ones. It is shown that unlike an individual hard waveguide, the aperture efficiency of such a waveguide in the array has a nonmonotonic dependence on the waveguide radius. The results characterizing the behavior of the aperture efficiency and cross-polarization level in a frequency band as well as the contribution of certain waveguide modes in the reflected power are presented and discussed. The examples of the element patterns corresponding to minimal cross polarization are also given     

Multifrequency Waveguide Orthomode Transducer

This paper presents the design and development of a multifrequency probe-coupled orthomode transducer (OMT) using a circular waveguide as the primary waveguide and a rectangular waveguide as the secondary waveguide. Design is presented for a common OMT operating at 6.6, 10.65, 18, and 21 GHz using four cascaded circular waveguide sections with different cross-sectional dimensions. An innovative design technique is used to minimize the inter-port coupling and to maximize the power in the dominant mode to get the required radiation performance at all the frequency bands using a common radiating aperture. The simulated and measured parameters of the OMT and the horn fed by this OMT have been presented.     

Orthomode transducers with a common circular waveguide

An efficient electrodynamic model and an optimization procedure for orthomode transducers based on a circular waveguide and step transitions in rectangular input arms is developed. The physical factors limiting the operating bandwidths of these transducers are determined. The effect of the number of sections in the step transitions on the characteristics of single-band transducers are investigated.     

Aperture matching of a dielectric loaded circular waveguide elementarray

An X-band phased array with dielectric-loaded circular waveguide elements was investigated. The aperture was designed to provide balanced scan characteristics for both the E- and H-planes. The results of an experimental study are presented in which the active impedance of the radiating element was matched by introducing a circumferential groove onto the dielectric plug. Both the aperture junction and the matching groove were measured to derive their respective equivalent circuits for `look-in' and `look-out' impedance transformations. The groove size and its location from the aperture were then optimized by a hybrid approach wherein the measured data and computer simulations were used to greatly reduce the shop time, lab tests, and the number of trials in the hardware development     

改进型圆-矩波导模式转换器的研究

在某些特定频段上,传统的圆-矩波导模式转换器无法满足其性能要求。针对这一问题,提出一种结构紧凑、反射系数小且波形转换效率高的改进型波导模式转换器,其工作在4.7 GHz,带宽800 MHz。采用切比雪夫阻抗法对其进行理论分析,并计算得到结构尺寸。最后测量结果与仿真结果吻合良好,在工作频带内电压驻波比均小于1.1,证明了该方法的可行性。