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We propose a novel numerically efficient model for accurate characterization of leaky modes in optical waveguides. Within the context of finite elements, the mesh boundaries are truncated using complex infinite elements (CIEs). The CIE is based on adopting the homogeneous solution of the wave equation with the shape function of infinite elements to accurately and physically model semi-infinite subdomains instead of placing an artificial layer such as PML. The proposed treatment can be easily implemented and requires less computational resources compared to other conventional mesh truncation methods. The accuracy and rigor of our approach are demonstrated through studying different leaky waveguides' configurations. [ABSTRACT FROM AUTHOR]

Analytical hybrid-mode dispersion relations of a lossy coaxial waveguide were rigorously analyzed using a mode-matching technique. In order to model a practical coaxial line with inevitable losses, we adopted an all-dielectric coaxial waveguide surrounded by the perfect electric conductor (PEC) boundary. The rigorous dispersion characteristics of the TM01, TE01, and EH11 modes were investigated for lossy coaxial waveguides filled with different electrical conductivities. Based on the exact solutions, approximate but accurate dispersion equations were proposed for the TM0p, TE0p, EHmp, and HEmp modes in order to estimate and compare the behaviors of complex propagation constants in the microwave and visible spectra.

In this work, an analytical study of the electromagnetic propagation in a complex medium-based suspended three-layer coplanar waveguide (CPW) is carried out. The study aims at a numerical calculation of the dominant hybrid mode complex propagation constant in the CPW printed on a bianisotropic substrate. The herein considered bianisotropy is characterized by full 3×3 tensors of permittivity, permeability and magnetoelectric parameters. The study is based on the numerical derivation of the Green's functions of such a complex medium in the spectral domain. The study is carried out using the Full Generalized Exponential Matrix Technique based on matrix-shaped compact mathematical formulations. The Spectral Method of Moments (SMoM) and the Galerkin's procedure are used to solve the resulting homogeneous system of equations. The effect of the chiral and achiral bianisotropy on the complex propagation constant is particularly investigated. Good agreements with available data for an anisotropic-medium-based suspended CPW structure are achieved. Various cases of chiral and achiral bianisotropy have been investigated, and particularly, the effect on the dispersion characteristics is presented and compared with cases of isotropic and bianisotropic Tellegen media.

In this work, an analytical study of the electromagnetic propagation in a complex medium-based suspended three-layer coplanar waveguide (CPW) is carried out. The study aims at a numerical calculation of the dominant hybrid mode complex propagation constant in the CPW printed on a bianisotropic substrate. The herein considered bianisotropy is characterized by full 3×3 tensors of permittivity, permeability and magnetoelectric parameters. The study is based on the numerical derivation of the Green's functions of such a complex medium in the spectral domain. The study is carried out using the Full Generalized Exponential Matrix Technique based on matrix-shaped compact mathematical formulations. The Spectral Method of Moments (SMoM) and the Galerkin's procedure are used to solve the resulting homogeneous system of equations. The effect of the chiral and achiral bianisotropy on the complex propagation constant is particularly investigated. Good agreements with available data for an anisotropic-medium-based suspended CPW structure are achieved. Various cases of chiral and achiral bianisotropy have been investigated, and particularly, the effect on the dispersion characteristics is presented and compared with cases of isotropic and bianisotropic Tellegen media. [ABSTRACT FROM AUTHOR]

The control of the radiation properties of a double-sided leaky-wave antenna (LWA) is demonstrated in this communication. To this aim, a standard substrate integrated waveguide (SIW) transmission line working with the TE20 mode is used. Due to the asymmetry of the radiated fields at both sides of the SIW, the equivalent magnetic currents generated are added in-phase at the center of the antenna, thus contributing to the radiation and improving the directivity in the $E$ -plane. Moreover, the complex propagation constant of the SIW LWA is properly controlled by means of the separation $P$ between posts, which mainly determines the leakage rate, and by the width $W$ of SIW, which mainly determines the pointing angle. In order to demonstrate this control, three prototypes radiating at different pointing angles (10°, 30°, and 50°) and same beamwidth (10°) have been manufactured and measured at the design frequency of 15 GHz. [ABSTRACT FROM AUTHOR]

The miniaturization of microwave and millimeter-wave components is necessary to meet demand for increasingly smaller integrated circuits. This paper explores the technique of capacitively loading the open side of a half-mode substrate-integrated waveguide (HMSIW) with a continuous ridge in order to lower the first-mode cutoff frequency and allow for substantial miniaturization. The full analytical calculation for the design of the first-mode cutoff frequency is presented, along with the extraction of the complex propagation constant and the analysis of the tradeoff between radiation and conductor losses. A comparison between the performance of the ridged HMSIW (RHMSIW) and HMSIW is simulated and measured, where the insertion loss of the RHMSIW is shown to be lower for frequencies up to 1.45 times the cutoff frequency fc , with a total width approximately 0.45 times the width of the HMSIW. The near-field radiation pattern is also measured, clearly illustrating the reduced radiation loss of the RHMSIW. A 3-dB coupler using the RHMSIW technology is designed, fabricated, and measured. The RHMSIW coupler’s performance is shown to be comparable to similar HMSIW and SIW designs in the literature, but with substantially improved miniaturization. The isolation of two parallel RHMSIWs in different configurations is also studied and compared with the HMSIW for use in applications requiring high-density routing or interconnection. It is shown that the capacitive ridge helps to reduce the crosstalk between neighboring transmission lines, allowing for the possibility of greater circuit densities, and further improving the miniaturization of microwave systems using the RHMSIW technology. To the best of our knowledge, the RHMSIW is the smallest waveguide-based transmission line with respect to wavelength presently in the literature. [ABSTRACT FROM PUBLISHER]

The electric and magnetic field distributions as well as the dispersion characteristics of open cylindrical tube (hollow-core) waveguides are analysed in this work. The analysed waveguides are made of an onion-like carbon (OLC) material. The solution of the boundary problem was fulfilled by the partial area method. It was discovered the very complicated dependencies of the phase and attenuation constants on the waveguide radii. Such dependencies arise because the OLC material is the highly dispersive and absorbing one. The fundamental and four higher modes can propagate in our investigated waveguides. We have analysed the high-frequency cut-off frequency of modes that is dependent on the tube waveguide external radius. The certain electromagnetic (EM) mode can propagate only on the frequencies lower than the mentioned cut-off frequency. For this reason, this cut-off frequency has an important use in practical applications. We presented here the EM field distributions of modes. We discovered that it is possible to reach the one-mode regime of OLC tube waveguide at the certain external radius. The fundamental and first higher modes’ EM energy is concentrated in the OLC material between the internal and external surfaces of the waveguide. [ABSTRACT FROM AUTHOR]

To explore fibre refractive index (RI) sensing based on radiation modes, the influences of ambient RI on radiation modes are investigated by a leaky mode approximation in a two‐layer fibre. Based on the analytical analysis and simulation results, it is identified that the change of ambient RI has no effect on the real part of the complex propagation constant of a leaky mode, but a remarkable effect on the imaginary part. More importantly, the influence of the medium's absorption loss on the imaginary part is almost negligible. If the medium's absorption loss is lower than 3.521 × 103 dB/cm, the induced average deviation rate of the imaginary part is <1.91%. [ABSTRACT FROM AUTHOR]

This communication demonstrates for the first time the capability to independently control the real and imaginary parts of the complex propagation constant in planar, printed circuit board compatible leaky-wave antennas. The structure is based on a half-mode microstrip line which is loaded with an additional row of periodic metallic posts, resulting in a substrate integrated waveguide SIW with one of its lateral electric walls replaced by a partially reflective wall. The radiation mechanism is similar to the conventional microstrip leaky-wave antenna operating in its first higher-order mode, with the novelty that the leaky-mode leakage rate can be controlled by virtue of a sparse row of metallic vias. For this topology it is demonstrated that it is possible to independently control the antenna pointing angle and main lobe beamwidth while achieving high radiation efficiencies, thus providing low-cost, low-profile, simply fed, and easily integrable leaky-wave solutions for high-gain frequency beam-scanning applications. Several prototypes operating at 15 GHz have been designed, simulated, manufactured and tested, to show the operation principle and design flexibility of this one dimensional leaky-wave antenna. [ABSTRACT FROM PUBLISHER]

A technique concerning the design and implementation of substrate integrated nonradiative dielectric (SINRD) waveguide is proposed in this paper. Different from the current SINRD waveguides, this scheme of making the SINRD guide structures directly out of the conventional printed circuit boards (PCBs) or similar platforms effectively eliminates cover metallic plates. This class of SINRD waveguides can be realized without resorting to a mechanical assembly as usually is done in the case of developing conventional nonradiative dielectric (NRD) guide circuits owing to the following two facts. First, increasing the width of the dielectric strip will decrease surface electric currents more significantly in the area of NRD strip. Second, the fabrication process and practical implementation are based on the concept of the substrate integration technique. In this case, air via-slot or via-hole arrays are created or punched directly on PCBs or metallized dielectric layers in order to fulfill the basic requirements of an SINRD waveguide design. By carefully choosing the SINRD dimensions and the pattern of via-slots or via-holes, potential leakage loss caused by these metallically uncovered via-slots or via-holes can be minimized and reduced to a negligible level. Therefore, the NRD waveguides can be designed and made through various processing techniques in a simple and practical manner for millimeter-wave and terahertz applications. In this paper, simulations and measurements have verified the proposed scheme. [ABSTRACT FROM PUBLISHER]

A novel approach is presented to solve an algebraic problem related to complex finite element analysis of periodic structures. This approach turns the quadratic eigen problem into a linear eigen problem of the same dimension and also exploits the sparsity of matrices which reduces the computation time enormously. An algorithm is also proposed that generates the dispersion diagram automatically. The method is applied to fairly simple singly, doubly, and triply periodic structures and the results agree well with those obtained by the dense-matrix approach. A more complicated device, a mushroom structure for use in the power distribution networks of electronic circuits, is also analyzed. The computational complexity of the new method is estimated to be n^1.6, where n is the dimension of the matrix problem. [ABSTRACT FROM PUBLISHER]

A metal cylindrical waveguide coated with an inside layer of lossy dielectric which affects the propagation characteristics of a guided electromagnetic mode is investigated for gyrotron-traveling-wave tube (gyro-TWT) amplifier applications. This paper reveals a series of novel phenomena. The dispersion curve of a higher order mode has a turning point during its evolvement from the fast wave region to the slow wave region. An electromagnetic mode in the lossy dielectric-coated waveguide exhibits a transverse partial-standing-wave distribution. The dielectric loss induces modal transition which results in the dispersion curves of a pair of nearby modes crossing each other and interchanging mode structures. Modal reduction caused by strong dielectric loss merges a pair of nearby modes into one. In this one merged mode, the dielectric-coated waveguide is equivalent to a conventional cylindrical waveguide with imperfect conducting wall. This improved understanding of lossy dielectric-coated metal cylindrical waveguide is of value and usefulness for application toward gyro-TWTs capable of high-power and wide bandwidth. [ABSTRACT FROM AUTHOR]

Abstract-A compact 2-D finite-difference frequency-domain (FDFD) method is proposed to analyze the propagation characteristics of arbitrary guiding structures. Unlike other FDFD methods, which calculate the propagation constant for a given frequency, this method adopts the technique that is usually used in the compact 2-D finite-difference time-domain method, i.e., extracting the eigen-frequency based on an initial phase constant. Similar with other FDFD methods, this method will lead to a standard eigenvalue problem. However, the difference equations of this method are much simpler compared to the previous methods. When being combined with the implicitly restarted Arnoldi technique, this method can be used to simulate large-scale guided-wave problems due to the significantly increased speed of calculation and the greatly decreased memory requirement. Besides, by means of the concept of an equivalent resonator, the method can also be used to calculate the attenuation constant of arbitrary guiding structures. [ABSTRACT FROM AUTHOR]

A compact two-dimensional (2-D) finite-difference time-domain (FDTD) method is proposed to analyze the propagation characteristics of arbitrary guiding structures. By transforming electromagnetic field variables into new forms of periodic variables, which also can be resolved from the Maxwell's equations, one can convert the 2-D transmission line problem into an equivalent resonator problem based on the idea of translating the transmission distance-related attenuation part of complex propagation constant into a time-dependent damping factor. As a result, the FDTD method for resonator can be made use of to simulate the lossy guiding structures. Attenuation constants can be obtained by means of the quality factors of equivalent resonators. It means that some leaky wave antennas can also be analyzed by using this method. Numerical simulations show that the proposed method can quickly and accurately extract the phase constants and attenuation constants of lossy guiding structures. [ABSTRACT FROM AUTHOR]

The finite-difference time-domain (FDTD) method incorporating an equivalent resonant cavity model is presented for the modeling and analysis of guided-wave propagation characteristics of complex periodic structures. By transforming electromagnetic field variables into a new set of periodic variables, which can also be resolved from the Maxwell's equations, one can convert a periodic guided-wave problem into an equivalent resonator problem. Thus, the FDTD method used for a resonant cavity problem can be adopted to simulate periodic guided-wave structures. In addition, the proposed FDTD algorithm can be extended to model lossy periodic propagation problems. In this study, the substrate integrated nonradiative dielectric waveguide, which is a special type of periodic guided-wave structure subject to a potential leakage loss due to its periodic gaps, is investigated as a showcase. The proposed method is first validated and is then used to analyze the guided-wave characteristics of substrate integrated nonradiative dielectric waveguides. It is shown that the substrate integrated nonradiative dielectric waveguide structure, which can easily be fabricated in planar form, has a well-behaved propagation property suitable for high-performance millimeter-wave circuit design. [ABSTRACT FROM AUTHOR]

In this letter, a method for the improved consideration of propagation losses in metallic waveguide structures is presented. The method relies on the perturbation of the boundary conditions on the metallic walls of the waveguides. Following this advanced technique, we are able to compute a complex modal propagation constant, thus avoiding the drawbacks of the classical power-loss method where losses associated to evanescent modes were not taken into account. A Computer Aided Design (CAD) software package based on such a modal analysis tool has been applied to predict the propagation loss effects in a Ka-Band rectangular waveguide filter. [ABSTRACT FROM PUBLISHER]

The leaky dispersion characteristics of a Goubau line were numerically investigated for three lower-order transverse magnetic (TM) modes by determining a complex propagation constant using Davidenko's method. As a result, physically meaningful spectral ranges of leaky modes were found to exist below the cutoff frequency of the Goubau line. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 523–525, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23136 [ABSTRACT FROM AUTHOR]

A theoretical study of the electromagnetic propagation in a complex medium suspended multilayer coplanar waveguide (CPW) is presented. The study is based on the generalized exponential matrix technique (GEMT) combined with Galerkin's spectral method of moments applied to a CPW printed on a bianisotropic medium. The analytical formulation is based on a Full-GEMT, a method that avoids usual procedures of heavy and tedious mathematical expressions in the development of calculations and uses matrix-based mathematical expressions instead. These particularities are exploited to develop a mathematical model for the characterization of wave propagation in a three-layer shielded suspended CPW structure. This study is based on the development of mathematical formulations in full compact matrix-based expressions resulting in Green's functions in a matrix form. The implemented method incorporates a new accelerating procedure developed in the GEMT which provides an initial value used to speed up searching for the exact solution in the principal computation code. This helped us to obtain accurate solutions with tolerable computing time. Good agreements have been achieved with the literature in terms of accuracy and rapid convergence. The results for different cases of bianisotropy have been investigated, and particularly, the effect on the dispersion characteristics is presented and compared with the isotropic case. [ABSTRACT FROM AUTHOR]

An improved semi-analytical model of a lossy microstrip transmission line is proposed. The model is based on the theory of the fundamental transverse magnetic mode of a lossy parallel-plate waveguide whose dielectric medium is assigned the effective permittivity of the respective lossless microstrip line. The complex propagation constant of the fundamental mode is computed by imposing the Leontovitch boundary condition at the upper and lower plates whose impedances take into account the thickness of the conductors and the current crowding effect. The dielectric loss is computed by perturbation formulas. The proposed model features high accuracy and computational efficiency at frequencies up to 100 GHz. [ABSTRACT FROM PUBLISHER]

The per unit length capacitance and inductance of a YIG-loaded microstrip line are computed in the frame of a quasi-transverse electromagnetic approach. The transmission line parameters, i.e., the complex propagation constant and the complex characteristic impedance are computed from them and the insertion loss of a finite-length YIG-loaded microstrip line is obtained using the simple transmission line model. In particular, it is shown that this model is suitable even for the magnetostatic regime. [ABSTRACT FROM PUBLISHER]

Wireless sensors for high temperature industrial applications and jet engines require RF transmission lines and RF integrated circuits (RFICs) on wide bandgap semiconductors such as SiC. In this paper, the complex propagation constant of coplanar waveguide fabricated on semi-insulating 4H-SiC has been measured through 813 K. It is shown that the attenuation increases 3.4 dB/cm at 50 GHz as the SiC temperature is increased from 300 K to 813 K. Above 500 K, the major contribution to loss is the decrease in SiC resistivity. The effective permittivity of the same line increases by approximately 5% at microwave frequencies and 20% at 1 GHz. [ABSTRACT FROM PUBLISHER]

In this letter, a unified method for computing the complex propagation constant γ of reflecting and nonreflecting lines is presented. The method uses a new matrix representation of the wave cascade matrix of a line having any characteristic impedance. To overcome the sign ambiguity problem inherent to the classical method some parameters of the fictitious XAM matrix are used and determined by the method itself. The success of the new procedure to resolve the sign ambiguity problem lies in the new matrix representation of the wave cascade matrix of a line having any characteristic impedance and in the reliable criterion to determine the am/cm and bm parameters of the fictitious XAM matrix. [ABSTRACT FROM PUBLISHER]