Improved FDTD tool for the analysis of arbitrarily thick HTCsuperconducting planar lines

An improved FDTD formulation is presented in order to simulate superconducting planar transmission lines of arbitrary thickness. These structures are usually analysed with a nonuniform mesh, which is very time consuming. The authors define a geometrical factor that accurately accounts for arbitrarily thick superconducting films, with no mesh in the strip cross-section     

Nonuniformly spaced linear and planar array antennas for sidelobe reduction

The material discussed can be divided into two parts. In the first part, an iteration method is presented for calculating the distances between the elements of a symmetrical nonuniformly spaced linear array antenna for sidelobe reduction. The amplitude of the excitation is assumed to be constant. The iteration method is applied to linear array consisting of 24 elements. After a few iterations, the sidelobe-to-mainlobe power ratio was reduced to over 22 dB from its value of 13.2 dB for uniform array spacing. In the second part, several symmetrical nonuniformly spaced planar array antennas have been designed, using the nonuniform linear array spacings of part one. The planar arrays include square-shaped and circular structures, with the number of elements ranging from 284 to 576. The iteration method discussed can be applied to linear arrays with any number of elements to obtain nonuniform grid spacings for sidelobe reduction. A number of planar grid structures can be constructed using the nonuniform linear grids. The nonuniform linear and planar arrays utilize fewer radiating elements and result in desirable sidelobe structures.     

Étude du couplage d’une onde électromagnétique externe et d’une ligne de transmission aérienne non uniforme

In this paper, a flexible and efficient method for analyzing the electromagnetic field to nonuniform multiwire aerial lines coupling is proposed. This analysis in based upon the finite- difference time- domain (fdtd) algorithm. The transient responses of nonuniform lines excited by different waves obtained by this method are compared with those of Spice and literature. The good agreement between all the simulation results validates the proposed approach.     

Minimization of reflection error caused by absorbing boundarycondition in the FDTD simulation of planar transmission lines

Residual reflection from absorbing boundaries introduces considerable error in the frequency-domain parameters of open-region planar transmission line components simulated in the time-domain. Various dispersive and super-absorbing boundary conditions have been developed to minimize this reflection. In this paper, a computationally efficient method, termed as geometry rearrangement technique (GRT), is proposed to correct the dominant reflection from absorbing boundaries by superposition of two subproblems with different source or boundary locations. The computational improvement of GRT is demonstrated by the FDTD simulation of dispersion in microstrip and coplanar transmission lines. A new method is discussed to accurately estimate the boundary reflection, and then applied to correct the characteristic impedance of planar transmission lines for boundary reflection     

Analysis of Microstrip-Like Transmission Lines by Nonuniform Discretization of Integral Equations

The nonuniform discretization of the integral equation on the tangential electromagnetic (EM) field on the boundary surface is proposed as a numerically efficient method to analyze the microstrip-like transmission lines. The calculated results of the propagation constant of the microstrip line based on this method are compared with other published analytical results. Various types of planar striplines are treated by the same formulas. The dominant and higher order modes of shielded microstrip line are discussed and compared with the longitudinal-section electric (LSE) and linear synchronous motor (LSM) modes of a two-medium waveguide.     

混合结构平面天线的输入阻抗

本文通过谱域途径分析计算了具有波导平面混合结构天线单元的输入阻抗,用等效传输线级联模型考虑了波导及喇叭不均匀性对内场的修正.而辐射损耗则用等效波数加以处理.驻波比的计算及实测结果一致性很好.     

A simplified computational procedure for the analysis of planar arrays

A simplified procedure for inverting the mutual impedance matrix of a uniform-spaced planar array of dipoles is presented. It relies on the special features of this matrix being symmetric block-Toeplitz and having a nilpotent off-diagonal part. Active radiation impedances and voltage standing-wave ratio (VSWR) values are then evaluated for various element positions and scan angles. The array-element patterns and far-field radiation patterns are then derived. Some specific examples are given to exhibit the significant reduction in computational effort. It is concluded that this method may be generalized to the analysis of higher order excitation modes and to nonuniform spaced arrays.     

Fast Numerical Computation of Green's Functions for Unbounded Planar Stratified Media With a Finite-Difference Technique and Gaussian Spectral Rules

A computational methodology for the calculation of Green's functions for unbounded planar stratified media is proposed in this paper. Unlike several techniques that are based on analytical calculations in the spectral domain, this one is based on a previously proposed finite-difference discretization of the corresponding one-dimensional differential equation and the resulting spectral matrix problem. A smart approximation of the radiation boundary condition, based on the mathematical methodology of Gaussian spectral rules and the associated construction of an optimal nonuniform grid in the unbounded space, succeeds in maintaining the tridiagonal nature of the matrix spectral problem, providing a highly efficient means of computing the desired multilayer Green's function     

Formulation générale de la méthode spectrale pour l’étude de structures planaires multicouches à tenseurs de permittivité et de perméabilité diagonaux

The materials usually used in microwave integrated circuits are often assumed isotropic. However, in certain cases anisotropy is introduced unintentionally during the manufacturing process, or deliberately in order to obtain non reciprocal devices, radar absorbers, and so on., or serves to improve circuit performances. In several cases, neglecting the anisotropy of certain substrates induces errors in integrated-circuit design. Hence the characteristics of planar structures containing anisotropic layers must be accurately described in order to secure the circuit design and improve the CAD models. On the other hand, the measurement of dielectric or magnetic anisotropy of materials at microwaves frequencies is of great interest for several applications and as such the planar structures on anisotropic layers can be used in this domain. Several methods enable the propagation characteristics to be calculated for a large number of structures such as microstrip, coplanar waveguides, and slotlines. The spectral domain technique (SDT) is one of the fastest. For anisotropic substrates, the formulation of the spectral domain method can be very difficult and it depends on the form of the relative tensors z and t. The main difficulty in considering anisotropic layers is to obtain the Green matrix of the spectral domain technique. The aim of this paper is to extent the SDT for 'planar lines on anisotropic (electric and/or magnetic) substrates. A generalized formulation for all diagonal and t is presented and used to calculate the propagation parameters for several planar lines.     

General principle of electrical equivalence for nonuniform transmission lines

The criterion of electrical equivalence for nonuniform transmission lines, introduced by Hellstrom, has recently been interpreted in a more general form. The letter presents the electrical-equivalence principle' in a simple manner. It is shown that any nonuniform RC (or LC) line may be made electrically equivalent to another RC (or LC) line, if the physical lengths of the two lines are properly chosen.     

Equivalent transformations for the mixed lumped Richards sectionand distributed transmission line

The authors introduce an analysis method for nonuniform transmission lines. Equivalent transformations between a circuit consisting of a cascade connection of a lumped Richards section, an ideal transformer, and a distributed transmission line and one consisting of a cascade connection of a class of a nonuniform transmission line, a lumped Richards section, and an ideal transformer, are given. Characteristic impedance distributions of these nonuniform transmission lines are expressed as hyperbolic or trigonometric functions. It is quite difficult to find the exact network functions of nonuniform transmission lines from the telegraph equation, but by using the equivalent transformation described it becomes possible to obtain exact network functions of a class of nonuniform transmission lines     

A Nonuniform Coaxial Line with an Isoperimetric Sheath Deformation

For impedance matching in transmission lines, nonuniform lines, obeying laws of taper like the exponential, the Dolph-Chebyshev etc., are used. For the nonuniform coaxial line, constructional advantages can be derived for the same electrical performance if it has a uniform circular inner conductor with an outer conductor having an isoperimetric transition, from circular to elliptic cross section, in conformity with the established laws of taper. This problem has been examined in the paper, and the required design formulas as well as the design charts are developed. The effect of an impedance and geometric discontinuity at the low-impedance junction of such a nonuniform line and the concentric circular uniform line is discussed. The use of the isoperimetric transition line in microwave components is indicated.     

Equivalent Circuits of Binomial Form Nonuniform Coupled Transmission Lines

Equivalent circuits of nonuniform coupled transmission lines whose self and mutual characteristic admittance distributions obey binomial form are presented. Telegrapher's equations of these nonuniform coupled transmission lines can he solved exactly rising Bessel functions of fractional order. By decomposing the chain matrix, it is shown that equivalent circuits of these nonuniform conpled transmission lines consist of cascade connections of lumped reactance elements, uncoupled uniform transmission lines and ideal transformers.     

Coupled Nonuniform Transmission Line and Its Applications

Theory and applications of coupled nonuniform transmission lines are described. Matrix representations of a general coupled nonuniform transmission line are presented, by means of which the behavior of any coupled nonuniform transmission line maybe completely described. Among a wide variety of applications of coupled nonuniform transmission lines, two typical networks, one the coupled nonuniform transmission-line folded all-pass network and the other the coupled nonuniform transmission-line directional coupler, are treated in detail. Equivalent circuit representatious of these two networks are presented, which enable the designer to synthesize them in a greatly simplified manner by making use of the theories now available for more conventional single nonuniform transmission lines. In addition, the properties of these two networks using coupled exponential line are investigated. Design procedure is also given for asymmetrical coupled exponential-line directional couplers having excellent characteristics.     

A computationally efficient nonuniform FIR digital filter bank for hearing aids

A computationally efficient nonuniform digital FIR filter bank is proposed for hearing aid applications. The eight nonuniform spaced subbands are formed with the help of frequency-response masking technique. Two half-band finite-impulse response (FIR) filters are employed as prototypes resulting in significant improvements in the computational efficiency. We show, by means of example, that an eight-band nonuniform FIR filter bank with stopband attenuation of 80 dB can be implemented with 15 multipliers. The performance of the filter bank is enhanced by optimizing the gains for each subband. The tests on various hearing loss cases suggest that the proposed filter achieves reasonable good matching between audiograms and magnitude responses of the filter bank at very low computational cost.     

Equivalent Representations of Nonuniform Transmission Lines Based on the Extended Kuroda's Identity

Kuroda's identity may be extended to circuits consisting of lumped reactance elements and nonuniform transmission lines. It is shown that these circuits are equivalent to circuits consisting of cascade connections of nonuniform transmission lines whose characteristic impedance distributions are different from original ones, lumped reactance elements, and ideal transformers. If a characteristic impedance distribution W(x) of an original nonuniform transmission line is given, a characteristic impedance distribution Z(x) of a transformed nonuniform transmission line may be uniquely obtained using W(x). Moreover, by using these equivalent transformations, network functions of these transformed nonuniform transmission lines can he derived exactly.     

Exponentially converging direct singular integral-equation methodsin the analysis of microslot lines on layered substrates

Two recently developed moment-method-oriented direct singular integral-equation techniques are used for the exact analysis of planar layered microslot lines. These techniques enable filling of all matrix elements via exponentially converging real-axis spectral integrals while retaining the simplicity of conventional moment methods. The proposed algorithms yield highly accurate results both for the propagation constants and for the modal surface magnetic currents with comparatively low computational cost     

端接非线性负载的非均匀传输线瞬态分析

在均匀多导体传输线的时域有限差分法(FDTD)基础上，对非均匀多导体传输线及端接非线性负载的情况进行了分析。结果表明：对于非均匀多导体传输线，采用FDTD法进行瞬态分析极为方便，并且可以处理端接非线性负载的情况；同时，还可获得线上各点的电压、电流波过程。通过实例验证了所提出的FDTD算法的有效性，可用于传输线波过程的研究。     

An efficient method for analysis of arbitrary nonuniformtransmission lines

The analytical solution of an ideal linear varied nonuniform transmission line (LNTL) has been obtained and the exact linear two-port ABCD matrix of LNTL has been given correctly for the first time. By using cascaded LNTL sections to approximate an arbitrary characteristic impedance profile, a new technique has been presented in this paper for analyzing an arbitrary nonuniform transmission line (NTL). The technique is far better than the conventional technique in terms of the computational accuracy and intensity since it uses a piecewise-linear characteristic impedance profile in place of the stepped profile used by the conventional technique. Several numerical examples have been given to demonstrate the method