Waveguide Discontinuities Research Articles

Multi-mode network analysis for discontinuities in parallel-plate waveguides partially filled with multi chiral rods

The reflection and transmission characteristics of the guided modes in parallel-plate waveguides partially filled with one or multi chiral rods have been investigated by a method, which combines the multimode network theory with a rigorous mode matching procedure. The formulas of the reflection and transmission coefficient matrix are derived. The numerical results for different cases are presented and have indicated that the chirality parameters and the gometrical dimensions of the chiral rods have significant influence on the reflection and transmission characteristics of the guided modes.

Propagation in photonic crystal coupled-cavity waveguides with discontinuities in their optical properties

An analytical model for propagation through and reflection from a discontinuity in coupled-cavity waveguides (CCWs) (also known as coupled-resonator optical waveguides—CROW) is developed. The theory is based on a modification of the tight-binding theory for propagation in nonuniform structures. Explicit analytic expressions for the reflection and transmission coefficients are obtained. These expressions resemble in form and structure the well-known Fresnel coefficients, with the traditional wave impedance parameter replaced by the device bandwidth. Matching of two uniform CCWs with the use of an intermediate serial section is also discussed, and an analogy to the well-known quarter-wavelength plate is pointed out.

A Rigorous Field Treatment for Multiport Waveguide Discontinuities

A rigorous field treatment for multiport waveguide discontinuities is presented in this article. This approach is a combination of the mode expansion method and finite element method, which is based on the weak form of the Helmholtz equation. Mode expansion is used other than PML (perfectly matched layers) to truncate the computing space of finite element. Multiport waveguide structures such as E-plane tee, E-H tee, and H-plane tee with a partial-height conducting post are studied as examples. Calculated results of these structures are shown and compared, respectively, to those in references. Good agreement has been observed.

A NOVEL MODELING TECHNIQUE TO SOLVE A CLASS OF RECTANGULAR WAVEGUIDE BASED CIRCUITS AND RADIATORS.

A new methodology has been developed, based on moment method; for analyzing a class of rectangular waveguide based circuits and radiators. The methodology involves in modeling the given structure using tetragonal bricks or cavities and then replacing all the apertures and discontinuities with equivalent magnetic current densities so that the given structure can be analyzed using only the Magnetic Field Integral Equation (MFIE). As it is necessary to use a number of such cavities in order to study these complicated waveguide structures, the present method is named as Multiple Cavity Modeling Technique (MCMT). The major advantage for using the MCMT in rectangular waveguide based structures is the fact that since only the magnetic currents present in the apertures are considered the methodology involves only solving simple magnetic field integral equations rather the coupled integral equation involving both the electric and magnetic currents. Further it is possible to consider both co and cross polarization and also the thickness of the waveguide discontinuities like diaphragm thickness or window thickness in the analysis. Due to this, it is possible to get highly accurate result. It is also possible to extend the method to any number of resonators, cavities or irises regardless of the polarization. To demonstrate, the methodology has been applied to analyze an open end of a waveguide with dielectric plug, both in transmitting and receiving mode, and a waveguide step discontinuity. Even mode and odd mode admittances of interacting identical inductive diaphragms have also been calculated using this methodology. Data obtained using this technique has been compared with measured, CST microwave studio simulation and literature available data. The theory has been validated by the reasonable agreement obtained between experimental data, simulated data and literature available data with numerical data.

A transformed TLM formulation for adjoint variable-based sensitivity analysis

We present a transformed formulation for the transmission-line modeling (TLM) method with nondispersive boundaries. This formulation enables efficient adjoint variable-based sensitivity analysis of lossless electromagnetic structures. The TLM simulation is cast in a form common to both the original and adjoint simulations. The same TLM simulator is used for both the original and adjoint problems with the only difference in the sources. Our proposed formulation is illustrated through estimating objective function sensitivities with respect to the physical dimensions of waveguide discontinuities.

Variational analysis of the disc-loaded waveguide slow-wave structures

The variational method is applied to calculate the dispersion characteristics of disc-loaded waveguide slow-wave structures. The parameters describing the waveguide discontinuities in disc-loaded waveguide are calculated by the variational method. Then the dispersion characteristics of slow-wave structures are obtained using lossless microwave quadrupole theory. Good agreement was observed between results of the variational method and those of field matching method and high frequency structure simulator. In the case of broad band, results of the variational method are better than those of field matching method.

An AVM technique for 3-D TLM with symmetric condensed nodes

We demonstrate, for the first time, the feasibility of the adjoint variable method (AVM) in three-dimensional (3-D) time-domain transmission-line modeling (TLM). Using only two 3-D simulations of the original and adjoint problems, the sensitivities of the objective function with respect to all design parameters are estimated. The AVM approach is applied to both perfectly conducting and dielectric discontinuities. Analytical derivatives of the symmetric condensed node (SCN) scattering matrix are utilized in the case of dielectric discontinuities to derive a semi-analytical adjoint system. Our approach is illustrated with waveguide discontinuities.

Photonic effects caused by multiple discontinuities in optical waveguides

The scattering properties of discontinuities between dielectric waveguides are obtained by using a new generalised scattering matrix concept, together with the generalised telegraphist equations formulism and the modal matching technique. There is no restriction either on the cross-section shape of the dielectrics or on the refractive index profile functions of the waveguides. Modal propagation characteristics, radiation losses and complex scattering coefficients between proper modes can be obtained for monomode and multimode dielectric waveguides connected in cascade. Results of the complex scattering coefficients were evaluated. Photonic bandgaps, photonic windows and optical switching properties were obtained for periodic structures at optical frequencies.

Reactance of hollow, solid, and hemispherical-cap cylindrical posts in rectangular waveguide

An accurate experimental technique is employed to determine the reactance of three commonly used symmetrical waveguide discontinuities: cylindrical posts with hollow, solid, and hemispherical-cap ends, and a useful data set is presented. Length adjustment factors are derived for the case of symmetrical excitation that relate the reactance of each post form. When used in conjunction with an existing analysis, it is shown that very accurate results can be predicted for the reactance of solid and hemispherical-cap posts.

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.

Analysis of finite-size coated electromagnetic bandgap structure by an efficient scattering matrix method

This paper presents an efficient simulation algorithm-Scattering matrix method for investigation of the coated finite two-dimensional electromagnetic bandgap (EBG) structures. The method is derived to be capable to simulate the band properties of the coated cylinder photonic crystal with wave discontinuities. Numbers of photonic crystals with waveguide discontinuities are examined. The transmission characteristics of the EBG embedded with metal, dielectric, and various coated cylinders are analyzed. The results show that the tuned bandgap properties are able to provide an additional possibility to develop a novel device.

Comprehensive study of CAD models of several coplanar waveguide (CPW) discontinuities

A comprehensive study of CAD models of several coplanar waveguide (CPW) discontinuities is presented. The following discontinuities are studied: CPW short-end, CPW open-end, symmetric CPW series gap, and symmetric short-end coupled CPW. Simple models, that are suitable for CAD purposes, are proposed and validated by comparison to published full-wave results.

EC-ANN models for CPW discontinuities

Novel accurate and efficient equivalent circuit trained artificial neural-network (EC-ANN) models, which inherit and develop advantages of EC models and EM-ANN models, have been developed for coplanar waveguide (CPW) discontinuities. Modelled discontinuities include CPW open stub, gap and air-bridge, for which validation tests are performed. These models allow for circuit design, simulation and optimisation within a CAD simulator.

Electromagnetic Material Characterization using a Partially-Filled Rectangular Waveguide

Electromagnetic material characterization measurements are an important aspect of modern design. Rectangular waveguides are often used in the material characterization process to facilitate measurement since they are readily available and because rectangular samples can be easily machined and placed in the cross-sectional plane of the waveguide for reflection and transmission testing and subsequently analyzed using a simple theory [1, 2]. However, this technique can produce unacceptably large errors for high loss or highly reflecting samples due to a poor signal-to-noise ratio (SNR) for the transmission measurement.In this paper, a partially-filled waveguide method is presented that enhances transmission quality and accuracy in electromagnetic material characterization measurements. The partially-filled waveguide geometry improves transmission but leads to the excitation of higher-order modes. A mode-matching technique is developed here to accommodate the resulting waveguide discontinuity and a Newton root search method is utilized to subsequently extract the electromagnetic properties of the test sample. Experimental measurements for several materials will be presented at X-band frequencies (8–12 GHz) to verify the theoretical analysis.

Efficient estimation of adjoint-variableS-parameter sensitivities with time domain TLM

We present a novel algorithm for efficient estimation of S-parameter sensitivities with the time-domain transmission line modelling (TLM) method. The original electromagnetic structure is simulated using TLM to obtain the S-parameters in the desired frequency band. For each port, an adjoint TLM simulation that runs backward in time is derived and solved. The sensitivities of the S-parameters in the desired frequency band are estimated using only the original and adjoint simulations. For a structure with Np ports and n designable parameters, our approach requires only Np additional simulations regardless of n. This can be easily contrasted with the 2nNp additional simulations required by the central difference approximation. Our algorithm is illustrated through the estimation of S-parameter sensitivities with respect to the dimensions of waveguide discontinuities. Very good match is obtained between our sensitivity estimates and those obtained using central difference approximation. Copyright © 2005 John Wiley & Sons, Ltd.

Hierarchical Vector Finite Elements with p-Type non-Overlapping Schwarz Method for Modeling Waveguide Discontinuities

Hierarchical Vector Finite Elements with p-Type non-Overlapping Schwarz Method for Modeling Waveguide Discontinuities

Analysis of waveguide discontinuities using a hybrid method combining the Helmholtz weak form and mode expansion

AbstractA new approach for the analysis of waveguide multiports discontinuities is presented in this paper. This approach is a combined method of the mode‐expansion method and finite‐element method, which is based on the weak form of the Helmholtz equation. We use a mode expansion technique other than PML to truncate the computing space of finite element. Multiport structures such as H‐Plane forked T‐junction, waveguide loaded with two dielectric posts, and E‐plane filter are studied as examples. The calculated results of these structures are shown and compared, respectively, to those in references. Good agreement between them is observed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 173–177, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20411

Series‐coupled microring resonator filters with embedded semiconductor optical amplifiers

AbstractBack reflections from series‐coupled optical microring resonator filters caused by waveguide discontinuities are numerically investigated and optimized. The focus is on small discontinuities, such as those that can be expected from GaInAsP/InP‐based semiconductor optical amplifiers (SOAs) embedded in ring resonators. Significant improvement of the return loss is obtained when the length of the SOA is appropriately chosen. The design principle is applied to both all‐pass (two‐port) and add/drop (four‐port) filters. The sensitivity of the design to fabrication parameters is discussed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 427–432, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20326

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.

Higher Order Large-Domain FEM Modeling of 3-D Multiport Waveguide Structures With Arbitrary Discontinuities

A highly efficient and accurate higher order large-domain finite-element technique is presented for three-dimensional (3-D) analysis of N-port waveguide structures with arbitrary metallic and dielectric discontinuities on standard PCs. The technique implements hierarchical polynomial vector basis functions of arbitrarily high field-approximation orders on Lagrange-type curved hexahedral finite elements of arbitrary geometrical orders. Preprocessing is carried out by a semiautomatic higher order meshing procedure developed for waveguide discontinuity problems. The computational domain is truncated by coupling the 3-D finite-element method (FEM) with a two-dimensional (2-D) modal expansion technique across the waveguide ports. In cases where analytical solutions are not available, modal forms at the ports are obtained by a higher order 2-D FEM eigenvalue analysis technique. The examples demonstrate very effective higher order hexahedral meshes constructed from a very small number of large curved finite elements (large domains). When compared to the existing higher order (but small domain) finite-element solutions, the presented models require approximately 1/5 of the number of unknowns for the same (or higher) accuracy of the results.