Approximate formulas for step discontinuities in circular waveguides

The authors discuss approximate formulas to determine the normalised impedance for a discontinuity between two concentric circular waveguides. These formulas are used for the computation of step transformers. Experimental results validate these approximations.<>     

Modal analysis of step discontinuities in graded-index dielectricslab waveguides

The modal solutions of the TE- and TM-modes of an arbitrary graded-index dielectric slab waveguide have been derived by applying the generalized telegraphist's equations to the equivalent inhomogeneous parallel-plate waveguide model with electric or magnetic walls. These modal solutions have been employed in a mode-matching procedure to calculate the transmission properties of step discontinuities in arbitrarily graded-index dielectric slab waveguides such as diffused optical waveguides having exponential, Gaussian and complementary error-function index profiles. For slab waveguides containing an abrupt offset, the radiated power is found to increase smoothly with increasing displacement. Power loss calculations for an abrupt change in diffusion depth for which the dominant mode is in the vicinity of cutoff, exhibit a sharp transition from almost zero loss to nearly total radiation loss     

Field-matching solution of transverse discontinuities in inhomogeneous waveguides

A mode-matching technique for analysing thin irises in homogeneous waveguides is extended for use in inhomogeneously filled waveguides. Numerical and experimental results are given for a thin iris in a dielectric-slab-loaded waveguide.     

Analysis of discontinuities in planar dielectric waveguides: aneigenmode propagation method

The eigenmode propagation method is proposed to analyze the discontinuity problems in planar dielectric waveguides. This recursive algorithm is based on the numerical mode matching method, but it uses less computation time and computer memory, which makes the analysis of multiregion, vertically stratified media much more effective. With this algorithm, the required computer memory is independent of the number of regions in the problem, and the computation time is linearly proportional to the number of regions. Therefore, it is particularly suitable for the analysis of planar waveguide discontinuities and waveguide bends. Using this method, larger problems can be analyzed which are impractical with the finite element method. Numerical examples are given to demonstrate that the computation time is linearly proportional to the number of discontinuities, while the computer memory is almost a constant independent of the number of discontinuities     

Step discontinuities on dielectric waveguides

Reflection, transmission and radiation properties of a step discontinuity on a dielectric surface waveguide are calculated. The method used involves bounding the open waveguide with perfect conductors. Results are compared with those given by previous authors.     

Modeling three-dimensional discontinuities in waveguides usingnonorthogonal FDTD algorithm

A generalization of the finite-difference time-domain (FDTD) algorithm adapted to nonorthogonal computational grids is presented and applied to the investigation of three-dimensional discontinuity problems. The nonorthogonal FDTD uses a body-fitted grid for meshing up the computation domain and, consequently, is able to model the problem geometry with better accuracy than is possible with the staircasing approach conventionally employed in the FDTD algorithm. The stability conditions for the nonorthogonal FDTD algorithm are derived in two an three dimensions. Numerical results, including an H-plane waveguide junction, a circular waveguide with a circular iris, a circular waveguide with a rectangular iris, and a microstrip bend discontinuity, are presented to validate the approach     

Matrix analysis of discontinuities in nonreciprocal waveguides: analytical description for magnetooptical slab waveguides

A new analytical formalism to study the effect of discontinuities in a nonreciprocal waveguide has been developed. The analysis is based on 1) the general orthogonality relation obtained from the reciprocity theorem, 2) the modal expansion of the transverse electromagnetic fields within the waveguide, and 3) the continuity of the tangential components of such electromagnetic fields at both sides of the discontinuity. The formalism is presented in a matrix form, which allows the treatment of several discontinuities as a simple summation and product of coupling and propagation matrices. The matrix formalism is developed for magnetooptic waveguides in the three different orientations of the magnetization, and, within this context, two practical applications of magnetooptic isolators are studied.     

Radiation modes and step discontinuities in dielectric ribwaveguide

The continuous spectrum of the rib waveguide is derived by a method that ensures orthonormality and completeness of the spectrum. A relatively simple approximation of this continuum for most cases of common interest is obtained. The theory is applied to the abrupt step discontinuity in the E-plane of the rib guide under LSE polarization and to the abrupt termination problem, including radiative effects never before investigated     

Equivalent network approach for multistep discontinuities inelectron waveguides

An analysis method is described for multistep discontinuities in electron waveguides composed of semiconductor heterostructures. The method is based on a rigorous mode-matching procedure that takes into account the effects of external finite potential and spatially varying effective mass. Stress is placed on network representations to establish physical pictures of the quantum effects and to yield insight; in addition, a systematic microwave network approach is employed. The equivalent network representation is given for the waveguide modes propagating normally to the step discontinuity, and the mode-matching procedure is described for the boundary-value problem of the step discontinuity. Combining the above two procedures, the super-cascade matrix formulation is carried out, from which the reflection and transmission characteristics of multistep discontinuities in electron waveguides can be estimated. In order to show the validity and usefulness of this approach, examples are computed for constriction structures composed of three-layered electron waveguides     

Adaptive neuro-fuzzy inference system for gap discontinuities in coplanar waveguides

A new approach based on an adaptive neuro-fuzzy inference system (ANFIS) is presented for gap discontinuities in coplanar waveguides (CPWs). The proposed ANFIS model combines the neural network adaptive capabilities and the fuzzy qualitative approach. The ANFIS is presented so as to produce a good approximation to the nonlinear relationship between the geometrical parameters and the frequency-dependent equivalent circuit parameter (the S ₂₁ parameter of the gap). The ANFIS results for the S ₂₁ parameters are compared with the results available in the literature obtained by using the conformal-mapping technique (CMT), and the results confirm that the proposed ANFIS model can provide an accurate computation of the S ₂₁ parameters of the gaps in CPWs.     

Bidirectional finite-element method-of-line beam propagation method(FE-MoL-BPM) for analyzing optical waveguides with discontinuities

A bidirectional finite-element method-of-line beam propagation method (FE-MoL-BPM) is newly proposed for analyzing optical waveguides with discontinuities including transmissions, reflections and radiations. In this approach, the finite-element method (FEM) is introduced to discretize the derivatives of the variable perpendicular to the propagation direction. Since the proposed method is accurate and stable, only a small number of nodal points are required     

The rigorous analysis of cascaded step discontinuities inmicrostrip

A rigorous analysis of boxed microstrip single-step discontinuities and cascades of strongly coupled discontinuities is presented. Use is made of a variational formulation involving the expansion of the transverse E field at the step in terms of suitable basis functions. Strongly coupled steps are analyzed using the concept of localized and accessible modes and making use of a network model. The method is applied to a five-section low-pass filter     

Modified residue calculus technique for microstrip step discontinuities

The modified residue calculus technique (MRCT) is applied to the analysis of the microstrip discontinuity problem based on the waveguide model. The method is numerically efficient and the accuracy checked against published data.     

A partial variational approach for arbitrary discontinuities inplanar dielectric waveguides

A novel approach for analyzing arbitrary discontinuities in planar dielectric waveguides is proposed that uses the finite-element method along with the frontal solution technique. On the basis of the partial variational principle (PVP), the fields interior and exterior to the discontinuity finite-element region can be treated independently and eventually can be coupled. The interior fields are expanded by the finite-element nodal values and the corresponding local bases, while the exterior ones are handled by an approach combining modal expansion and Green's function. In numerical computation, the continuous spectra of the waveguide modes are discretized by the Laguerre expansion method. To check the correctness of the present analysis, two numerical results are compared to those of other methods. The scattering characteristics of several linearly tapered discontinuities, such as transformers and feed structures, are analyzed and compared to those having step junctions     

Study of microstrip step discontinuities on bianisotropicsubstrates using the method of lines and transverse resonance technique

A hybrid approach, combining the method of lines (MoL) and transverse resonance technique (TRT), is presented for the analysis of microstrip step discontinuities that are printed on uniaxial or biaxial bi-anisotropic substrates. The method of lines, formulated in terms of Kronecker products, is used to determine the characteristic equation for the resonant length. The transverse resonance technique is applied to obtain the S-parameters of the junction by casting the discontinuity problem as a microwave equivalent network. Good agreement is found between results of the MoL/TRT approach and those obtained by other methods. Effects of individual tensor elements of the substrate on the scattering parameters of the discontinuity are investigated at selected frequencies. The proposed MoL/TRT approach is found to converge very fast and does not require excessive computer memory, with all computations performed on a 486DX-50 MHz PC     

Transient response of microstrip step discontinuities on anisotropic substrate

In this paper, we present the numerical simulation of transient response of short pulse propagating through a microstrip step junction on anisotropic substrate having a tilted optical axis. In the simulation, the FD-TD method is extended to treat the cases having tilted optical axis expressed by a permittivity tensor with off-diagonal elements. The results show that the dispersion of transient signal caused by microstrip step discontinuities is quite significant and the dependence of transient characteristics of microstrip lines on the tilted angle of optical axis for anisotropic substrate can not be neglected.     

Pseudoreversibility condition for minimizing radiation loss at discontinuities of coupled waveguides

A design condition is derived for lossless discontinuities of coupled waveguides by finding solutions, which satisfy time reversibility of guided modes. The derived condition is used as a bound for minimizing radiation loss. Even when there is strong coupling between guided modes, the radiation loss can be minimal. A comparison between different grating designs in a 2 /spl times/ 2 backward coupler demonstrates that two coherently coupled gratings can significantly reduce radiation loss, as compared to a single grating.     

Numerical analysis of arbitrarily shaped discontinuities betweenplanar dielectric waveguides with different thicknesses

An approach that combines the finite-element and boundary-element methods is applied to the analysis of arbitrarily shaped discontinuities between planar dielectric waveguides with different thicknesses. The fields interior and exterior to the region enclosing the discontinuities are treated by the finite-element method and the boundary-element method, respectively. The waveguide regions connected to the discontinuities are handled by analytical solutions. In this approach, scattering characteristics of the discontinuities can be accurately evaluated, and far-field radiation patterns can be easily calculated. To show the validity and usefulness of this approach, the scattering characteristics of a step, a staircase transformer, and a tapered transformer are analyzed. Also, a simple equivalent network approach is introduced for estimating the reflection and transmission characteristics of planar dielectric waveguide discontinuities, and the effectiveness of this simple approach is confirmed by comparing the numerical results with those of the approach that combines the finite-element and boundary-element methods     

A new hybrid mode-matching/numerical method for the analysis ofarbitrarily shaped inductive obstacles and discontinuities inrectangular waveguides

A new and efficient hybrid mode-matching method is presented for the analysis of arbitrarily shaped inductive obstacles and/or discontinuities in a rectangular waveguide. The irregular region with obstacles and/or discontinuities is characterized using a full-wave hybrid spectral/numerical open-space technique expanding the fields in cylindrical wave functions. Next, a full-wave mode-matching procedure is used to match the cylindrical wave functions to guided modes in all ports and a generalized scattering matrix for the structure is finally obtained. The obstacles can be metallic or dielectric with complex permittivities and arbitrary geometries. The structure presents an arbitrary number of ports, each one with different orientation and dimensions. The accuracy of the method is validated comparing with results for several complex problems found in the literature. CPU times are also included to show the efficiency of the new method     

Characteristics of inhomogeneously filled double L-septa waveguides

Three types of inhomogeneous double L-septa guide (DLSG) produced by selective dielectric loading of the different regions are analyzed. The cutoff and bandwidth characteristics of these configurations are compared with the inhomogeneous T-septa guide and homogeneous DLSG. An optimum configuration with very large bandwidth emerges as a potential structure for practical implementation