非均匀传输线特性重构中的噪声影响分析

利用时域反射技术(Time Domain Reflectometry,TDR),由测量得到的时域反射信号,可以重构出非均匀传输线的一些特征参数。当反射信号中混有噪声时,对非均匀传输线特性参数的重构会产生影响。采用Zakharov-Shabat类型逆散射问题的数值反演算法,以指数型非均匀传输线为例,对时域反射信号中混有高斯白噪声情况下的非均匀传输线特性参数重构问题进行了数值实验。数值计算结果表明,在噪声干扰下,算法本身是稳定的,在较宽的信噪比范围内,能有效地重构出非均匀传输线的特征参数。     

Time-domain reflectometry using arbitrary incident waveforms

A novel time-domain reflectometry technique is developed for detecting the physical structures of transmission lines by using arbitrary waveforms. By discretizing both incident and reflected waves, we formulate the reflection coefficient of a nonuniform transmission line as a polynomial ratio in the Z-transform, wherein the numerator and denominator represent the reflected and incident waves, respectively. A reconstruction scheme is derived to obtain the characteristic impedance profile of a transmission line. Some examples are presented to illustrate the validity of this new technique.     

Nonuniformly coupled microstrip transversal filters for analog signal processing

The Fourier transform relationship between frequency response and impedance profile for single nonuniform transmission lines is used to derive the time-domain step response of single and coupled nonuniform lines. The expression for the step response of a characteristically terminated nonuniformly coupled transmission line structure is shown to correspond to the characteristic impedance profile. By using this relationship, any arbitrary step response can be realizing by utilizing nonuniformly coupled strip or microstrip lines for possible applications as waveform-shaping networks and chirp filters. A numerical procedure to compute the step response of the nonuniform coupled line four-port is also formulated in terms of frequency-domain parameters of an equivalent cascaded uniform coupled line model with a large number of sections. Sinusoidal and chirp responses are presented as examples that are readily implemented using coupling microstrip structures. The step response of an experimental nonuniformly coupled microstrip structure is presented to validate the theoretical results.<>     

Arbitrary pulse shape synthesis via nonuniform transmission lines

A discrete inverse scattering technique is used to define the impedance profile for a nonuniform transmission line which reflects an arbitrary waveform. Initially charged nonuniform lines, switched out into a general load, can also be synthesized by this method, and are discussed. The direct or layer peeling algorithm is applied to generate profiles which are subsequently analyzed using the one-dimensional finite difference method and fabricated in stripline. Excitation for the nonuniform line is done by using a charged line connected to a photoconductive Si switch triggered by a mode-locked YLF laser. Several lines were fabricated relevant to amplitude modulation of the master oscillator laser pulse for fusion experiments. Using the layer peeling method, a complex high-voltage pulse shape for use in laser fusion experiments is synthesized to an extraordinary degree of precision. It is possible to generate any arbitrary pulse shape by reflecting a step pulse off a synthesized nonuniform transmission line provided the power spectrum of the reflected pulse does not exceed that of the input pulse at any frequency     

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.     

非均匀传输线的仿真模型建立方法研究

利用分段线性和等效电路模型,结合Hspice电路仿真软件,提出了一种建立非均匀传输线仿真模型的方法,给出了非均匀传输线的Hspice等效电路模型。通过一个有代表性的算例,利用文中提出的仿真模型建立方法,得出了时域范围内的Hspice仿真结果。最后通过与已有的方法结果比较表明：该方法有较高的计算精度,且计算速度快,占用计算机资源少。     

Synthesis of nonuniform transmission lines with terminaldiscontinuities

An integral equation was previously derived by the authors (ibid., vol.AP-34, p.546-53, Apr. 1986) for the inverse problem associated with finite-length nonuniform lines having known impedance discontinuities at the input and output. A procedure for determining the characteristic impedance profile of the line from the solution of the integral equation was also presented. Here, the numerical aspects of this inverse problem are treated. This equation is solved using general expansions of both the kernel and unknown functions, thereby reducing the integral equation to a system of linear algebraic equations. This makes possible a numerical implementation of the theory by which the impedance profile of a nonuniform line may be reconstructed from given spectral data. The realizability aspects of the problem are treated and several examples of computer-assisted profile inversion are presented     

Capacitance of nonuniform coaxial transmission lines

The physical realisation of a nonuniform transmission line. possessing some desirable characteristic impedance profile, is usually achieved using calculations which do not take into account the expanding or contracting nature of the line and the associated distortions of the electromagnetic fields. A method has been devised which gives an improved realisation of such lines in a coaxial configuration. Corrections for the conductor slopes and effective lengths are made and a design example is used to illustrate these effects.     

A lower bound for the length of nonuniform transmission line matching sections

A lower bound for the length of a nonuniform transmission line section needed to match a given load impedance to a given real input impedance is derived. The bound depends not only on the load and input impedances, but also on the maximum and minimum permissible values of characteristic impedance within the nonuniform line. Several specific cases are presented to illustrate the tightness of the bounds.     

Impedance Transformation Equations for Exponential, Cosine-Sqaared, and Parabolic Tapered Transmission Lines

Closed-form equations that give the value of an arbitrary complex impedance transformed through a length of dissipationless, nonuniform transmission line with exponential cosine-squared, and parabolic taper are presented. These equations are obtained by a second order nonlinear differential (Riccati) equation relating impedance, the nonuniform line impedance and the line length. The results presented should be useful in solving impedance matching problems.     

非均匀传输线综合的特征法

本文利用特征法对无耗非均匀传输线进行了综合。在二倍于传输线延时的时间范围内给定时域反射电压响应的ｍ个取样值，则非均匀传输线可由ｍ段长度不等、延时为相应时间取样间隔的均匀线近似，各均匀传输线段的特性阻抗唯一求出。     

非均匀宽带阻抗变换器优化设计

当对阻抗变换器总长度有一定限制时 ,传统的均匀宽带阻抗变换器中的特性阻抗可能超出实际能实现的范围 ;对于非均匀宽带阻抗变换器 ,由于取消了对每段传输线长度的限制 ,设计时有了更大的自由度 ;为了得到最佳的传输线网络参数 ,采用了混合遗传算法进行优化设计 ,引入了动态惩罚函数对适应度函数进行处理 ;数值仿真表明 :用该方法设计的宽带匹配变换器的性能优于现有的其它设计方法     

Transient analysis of nonuniform, high-pass transmission lines

The transient behavior of nonuniform transmission lines is studied by investigating the step response of a cascaded multiple-section line. The first arriving wave and the transition ripple at the load end are examined in detail. It is found that the characteristic impedances necessary for obtaining the maximum first arriving wave are the same as those of the conventional multiple-section, quarter-wave transformer. The discrete characteristic impedances of the multiple-section line are then extended to a continuously varied impedance function of a tapered line. The high-pass characteristic of the tapered nonuniform line is verified with techniques in the frequency domain     

Analyse temporelle des lignes de transmission non uniformes avec effet de peau

This paper deals with a computational approach, based upon centered points finite-difference time-domain technique, for evaluating voltages and currents along nonuniform planar transmission lines terminated with arbitrary loads. To improve the accuracy of the method, the skin effect has been included into the algorithm by means of the approximation of the conductor internal impedance. Some configurations of nonuniform planar lines have been analyzed in order to show different aspects of the efficiency of this computational procedure.     

A Parallel-Strip Ring Power Divider With High Isolation and Arbitrary Power-Dividing Ratio

In this paper, a new power divider concept, which provides high flexibility of transmission line characteristic impedance and port impedance, is proposed. This power divider is implemented on a parallel-strip line, which is a balanced transmission line. By implementing the advantages and uniqueness of the parallel-strip line, the divider outperforms the conventional divider in terms of isolation bandwidths. A swap structure of the two lines of the parallel-strip line is employed in this design, which is critical for the isolation enhancements. A lumped-circuit model of the parallel-strip swap including all parasitic effects has been analyzed. An equal power divider with center frequency of 2 GHz was designed to demonstrate the idea. The experimental results show that the equal power divider has 96.5% -10-dB impedance bandwidth with more than 25-dB isolation and less than 0.7-dB insertion loss. In order to generalize the concept with an arbitrary power ratio, we also realize unequal power dividers with the same isolation characteristics. The impedance bandwidth of the proposed power divider will increase with the dividing ratio, which is opposite to the conventional Wilkinson power divider. Unequal dividers with dividing ratios of 1 : 2 and 1 : 12 are designed and measured. Additionally, a frequency independent 180 power divider has been realized with less than 2 phase errors.     

A genetic approach to the synthesis of composite right/left-handed transmission line impedance matching sections

A genetic approach for the synthesis of composite right/left-handed (CRLH) transmission line impedance matching sections is presented. Continuous parameter genetic algorithm (CPGA) is used for the synthesis. Examples for a uniform CRLH transmission line impedance matching section and a nonuniform CRLH transmission line impedance matching section are given.     

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     

Equivalent transformations for the mixed lumped Brune-type sectionand uniform transmission line

As an analytical method for nonuniform transmission lines (NTLs) equivalent transformations are extended to a more general case, namely a mixed lumped Brune-type section and a uniform transmission line (unit element, UE). Circuits consisting of a cascade connection of a lumped Brune section and a UE are equivalent to one consisting of a cascade connection of a nonuniform transmission line whose characteristic impedance distribution is expressed with a trigonometric function and a lumped Brune section. This equivalent transformation method is easily applied to a circuit consisting of a lumped C section and a UE. The equivalent circuit is a circuit consisting of an NTL and a lumped C section. In this case, the characteristic impedance distribution of the NTL may be expressed in terms of a hyperbolic function. Exact network functions of the NTLs are easily obtained from the equivalent circuits without solving the telegrapher's equation. By considering the limiting case of these equivalent transformations, equivalent transformations for circuits consisting of a cascade connection of a lumped resonance circuit and a circuit and a uniform transmission line are derived     

Comments on "Transmission Line Impedance Matching Using the Smith Chart" (Letters)

For the recently discussed problem of R. M. Arnold of finding the characteristic impedance and electrical length of a uniform, loss-free transmission line which transforms a given impedance into another given impedance, an alternate approach using an elementary auxiliary calculation (with no trial and error) has been given in.     

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.