Zicong Mei

Time and Frequency Domain Solutions of EM Problems: Using Integral Equations and a Hybrid Methodology

Preface. Acknowledgments. List of Symbols. Acronyms. Chapter 1 Mathametical Basis of a Numerical Method. Chapter 2 Analysis of Conducting Structures in the Frequency Domain. Chapter 3 Analysis of Dielectric Objects in the Frequency Domain. Chapter 4 Analysis of Composite Structures in the Frequency Domain. Chapter 5 Analysis of Conducting Wires in the Time Domain. Chapter 6 Analysis of Conducting Structures in the Time Domain. Chapter 7 Analysis of Dielectric Structures in the Time Domain. Chapter 8 An Improved Marching-on-in-Degree (MOD) Methodology. Chapter 9 Numerical Examples for the New and Improved Marching-on-in-Degree (MOD) Method. Chapter 10 A Hybrid Method Using Early-Time and Low-Frequency Information to Generate a Wideband Response. Appendix User Guide for the Time and Frequency Domain EM Solver Using Integral Equations (TFDSIE). Index. About the Authors.

Design and Testing of a Single-Layer Microstrip Ultrawideband 90 ° Differential Phase Shifter

This letter proposes a design of single-layer microstrip ultrawideband (UWB) 90^° differential phase shifter. The operating bandwidth covers the UWB frequency range from 3.1-10.6 GHz. The design is optimized using a transmission line model and an electromagnetic model, and have been fabricated using a plotter dealing with generation of printed circuits. The measured <i>S</i>₁₁ is better than -10 dB and <i>S</i>₂₁ is better than -0.96 dB within the UWB frequency range. The simulated and measured phase deviation of the differential phase shift are 90^°±5.23^° and 90^°±9.02^°, respectively. The advantages of the proposed design are the simple fabrication, low insertion loss, and broad bandwidth.

Transient Wave Propagation in a General Dispersive Media Using the Laguerre Functions in a Marching-on-in-Degree (MOD) Methodology

The objective of this paper is to illustrate how the marching-on-in-degree (MOD) method can be used for e-cient and accurate solution of transient problems in a general dispersive media using the flnite difierence time-domain (FDTD) technique. Traditional FDTD methods when solving transient problems in a general dispersive media have disadvantages because they need to approximate the time domain derivatives by flnite difierences and the time domain convolutions by using flnite summations. Here we provide an alternate procedure for transient wave propagation in a general dispersive medium where the two issues related to flnite difierence approximation in time and the time consuming convolution operations are handled analytically using the properties of the associate Laguerre functions. The basic idea here is that we flt the transient nature of the flelds, the permittivity and permeability with a series of orthogonal associate Laguerre basis functions in the time domain. In this way, the time variable can not only be decoupled analytically from the temporal variations but that the flnal computational form of the equations is transformed from FDTD to a FD formulation in the difierential equations after a Galerkin testing. Numerical results are presented for transient wave propagation in general dispersive materials which use for example, a Debye, Drude, or Lorentz models.

An Improved Marching-on-in-Degree Method Using a New Temporal Basis

The marching-on-in-degree (MOD) method has been presented earlier for solving time domain electric field integral equations in a stable fashion. This is accomplished by expanding the transient responses by a complete set of orthogonal entire domain associated Laguerre functions, which helps one to analytically integrate out the time variable from the final computations in a Galerkin methodology. So, the final computations are carried out using only the spatial variables. However, the existing MOD method suffers from low computational efficiency over a marching-on-in-time (MOT) method. The two main causes of the computational inefficiency in the previous MOD method are now addressed using a new form of the temporal basis functions and through a different computational arrangement for the Greens function. In this paper, it is shown that incorporating these two new concepts can speed up the computational process and make it comparable to a MOT algorithm. Sample numerical results are presented to illustrate the validity of these claims in solution of large problems using the MOD method.

A Study of Negative Permittivity and Permeability for Small Sphere

When analyzing a small dielectric sphere with Mies series or at low frequencies, we will have singularities if the permittivity or permeability is -2. This letter shows that for electrodynamic situation, this singularity is only a result of error in the asymptotic analysis and will not appear in actual cases. However, for the electrostatic case, if one can create a permittivity of -2, this singularity does result in an infinite field.

Choice of the Scaling Factor in a Marching-on-in-Degree Time Domain Technique Based on the Associated Laguerre Functions

In marching-on-in-degree time domain method of moment, the transient responses are often expanded by a finite number of associated Laguerre functions. There is an error associated in truncating the associated Laguerre function series beyond that what is necessary in the solution process. This error is related to the scaling factor used in the argument of the associated Laguerre functions that actually approximates the unknown temporal variations. A least upper bound of this error is deduced. Based on this bound, one can obtain an optimum scaling factor to minimize this error so that it is guaranteed to be below a certain bound.

Design of a two-element folded-Yagi antenna with super-directivity

This paper presents a new design of the Yagi antenna with a super-directivity of 8.9dBi. The Yagi antenna has two folded elements; one is a fed element and the other is a parasitic element. Except the high directivity, this antenna also shows quite good input impedance and return loss performance at the working frequency of 300MHz. The 10dB fractional bandwidth is only about 1.3%, which restricts it to be narrow band application.

The Design of an Ultrawideband T-Pulse With a Linear Phase Fitting the FCC Mask

A discrete finite time domain pulse is designed under the constraint of the Federal Communications Commission (FCC) ultrawideband (UWB) spectral mask. This pulse also enjoys the advantage of having a linear phase over the frequency band of interest and is orthogonal to its shifted version of one or more baud time. The finite time pulse is designed by an optimization method and concentrates its energy in the allowed bands specified by the FCC. Finally, an example is presented to illustrate how these types of wideband pulses can be transmitted and received with little distortion.

Analysis of Arbitrary Frequency-Dependent Losses Associated With Conducting Structures in a Time-Domain Electric Field Integral Equation

The objective of this letter is to present a solution methodology for the analysis of arbitrary frequency-dependent losses on conducting structures in a time-domain electric field integral equation. The analysis of arbitrary frequency-dependent losses is incorporated in the newly developed marching-on-in-degree (MOD) method to solve the time-domain electric field integral equation. The novelty of this methodology is that both the arbitrary temporal dependence of the frequency-dependent losses and the transient current variations on the conducting structures are expanded in terms of the causal orthonormal associated Laguerre functions. The advantage of implementing these temporal expansion functions is that the convolution between two functional variations, namely the loss factor and the current density, can be treated in an analytical fashion resulting in an accurate and efficient solution methodology. Numerical examples dealing with both time-varying concentrated loads and skin-effect losses on electrically large conducting structures are analyzed to illustrate the potential of this method.

Time-domain method of moments accelerated by Adaptive Cross Approximation algorithm

This paper presents the Adaptive Cross Approximation (ACA) method combined with Time-Domain MoM (TD-MoM) to analyze the transient electromagnetic problem. On one hand, Marching-on-in-degree (MOD) method is used in TD-MoM to solve the TD-integral equations so that the disadvantage of late-time instability in Marching-on-in-time (MOT) method is avoided. On the other hand, the ACA algorithm is purely algebraic so that it can be easily applied to TD-MoM to accelerate the calculation and to reduce the CPU memory required for storing the data. Through a numerical example, this papers method is proven feasible and efficient.