An Ping Zhao

Application of a simple and efficient source excitation technique to the FDTD analysis of waveguide and microstrip circuits

A simple, efficient, and unified source excitation scheme for the finite-difference time domain (FDTD) analysis of both waveguides and microstrip circuits is developed and validated. In this scheme, by moving the source plane several cells inside the terminal plane and adding the excitation wave as an extra term in the FDTD equation, the interaction between the excitation and reflected waves are totally separated in time domain. Hence, for both waveguide and microstrip discontinuities, absorbing boundary conditions can be applied on the terminal plane directly. In particular, for microstrip circuits, our scheme does not induce any source distortions when a simplified field distribution is used as the excitation. Consequently, the terminal plane can be moved very close to the discontinuity and thus significant computational savings are achieved. In addition, for microstrip systems, the validity and efficiency of the Meis simplified field distribution are evaluated and confirmed for the first time.

Analysis of the numerical dispersion of the 2D alternating-direction implicit FDTD method

The numerical dispersion property of the two-dimensional alternating-direction implicit finite-difference time-domain (2D ADI FDTD) method is studied. First, we notice that the original 2D ADI FDTD method can be divided into two sub-ADI FDTD methods: either the x-directional 2D ADI FDTD method or the y-directional 2D ADI FDTD method; and secondly, the numerical dispersion relations are derived for both the ADI FDTD methods. Finally, the numerical dispersion errors caused by the two ADI FDTD methods are investigated. Numerical results indicate that the numerical dispersion error of the ADI FDTD methods depends highly on the selected time step and the shape and mesh resolution of the unit cell. It is also found that, to ensure the numerical dispersion error within certain accuracy, the maximum time steps allowed to be used in the two ADI FDTD methods are different and they can be numerically determined.

A fast and efficient FDTD algorithm for the analysis of planar microstrip discontinuities by using a simple source excitation scheme

A fast solution FDTD algorithm with a simple and efficient excitation scheme for the analysis of microstrip circuits is introduced. In this algorithm, the source plane is located several nodes inside the near-end terminal plane and absorbing boundary conditions (ABCs) can be applied on the terminal plane directly, without any special treatment. In addition, with this excitation scheme, no dc source distortions are induced on the source plane and nearby. Consequently, the terminal plane can be moved very close to the discontinuity, even at one-cell beyond the input/output reference planes. Hence, very significant computational savings can be achieved. To demonstrate the validity and efficiency of this algorithm, numerical results for a typical discontinuous microstrip structure are given and compared with those obtained by the conventional FDTD method. >

An efficient FDTD algorithm for the analysis of microstrip patch antennas printed on a general anisotropic dielectric substrate

In this paper, an efficient three-dimensional finite-difference time-domain (FDTD) approach based on the D-, E-, and H-fields is proposed to handle arbitrary anisotropic dielectric media; and, particularly, the way of imposing the electric-wall boundary condition on the surface of perfect electric conductors is discussed in detail. By combining the proposed FDTD approach with the material-independent perfectly matched-layer absorbers, the performance of a line-fed microstrip patch antenna deposited on general anisotropic dielectric substrate is investigated. The scattering parameters of the antenna as a function of the rotation angle of the optical axis of the anisotropic substrate are presented for the first time. Numerical results demonstrate how the resonant frequencies of the antenna are influenced by the anisotropy.

Generalized material-independent PML absorbers for the FDTD simulation of electromagnetic waves in arbitrary anisotropic dielectric and magnetic media

To simply and effectively absorb waves propagating in anisotropic materials consisting of both arbitrary permittivity and permeability tensors, generalized material-independent perfectly matched layer (GMIPML) absorbers are proposed. Within the GMIPML absorbers, electric displacement D and flux density B are directly absorbed, whereas electric field E and magnetic field H are simultaneously absorbed through the relations between E and D as well as H and B. The proposed GMIPML absorber is validated by analyzing two-dimensional (2-D) hybrid waves.

Generalized-material-independent PML absorbers used for the FDTD simulation of electromagnetic waves in 3-D arbitrary anisotropic dielectric and magnetic media

By introducing the material-independent quantities (electric displacement D and flux density B) into the finite-difference time-domain (FDTD) model, a generalized-material-independent perfectly matched layer (GMIPML) absorber used to absorb electromagnetic waves propagating in three-dimensional (3-D) general anisotropic dielectric and magnetic media is proposed. Within the proposed GMIPML absorber, D and B are directly absorbed, whereas E and H are simultaneously absorbed through the relations between E and D, as well as H and B. It is shown that with the help of this GMIPML absorber, Berengers perfectly matched layer (PML) absorbing boundary condition (ABC) can be simply and effectively extended to 3-D arbitrary anisotropic materials consisting of both arbitrary permittivity and permeability tensors.

Relationship between the compact complex and real variable 2-D FDTD methods in arbitrary anisotropic dielectric waveguides

The relationship between the compact complex and real variable 2-D FDTD methods used for the analysis of guided modes of arbitrary anisotropic dielectric waveguides is investigated. Situations for the permittivity tensor with different non-zero elements are discussed. It is found that in certain cases the complex 2-D FDTD method cannot be reduced to the real variable one. This, in turn, reveals that the real variable 2-D FDTD method has limitation when applied to arbitrary anisotropic dielectric waveguides. In addition, numerical results show that using the complex impulse in the excitation is not an essential condition, even for a purely complex 2-D FDTD method.

Extension of Berenger's PML absorbing boundary conditions to arbitrary anisotropic magnetic media

To simply and effectively absorb waves propagating in arbitrary anisotropic magnetic media, a material independent perfectly matched layer (MIPML) absorber is proposed. Within this MIPML absorber, conductivities /spl sigma//sup E/ and /spl sigma//sup B/ (instead of /spl sigma//sup E/ and /spl sigma//sup H/) are used. This results in that electric field E and magnetic flux density B are directly absorbed by the proposed absorber, whereas magnetic field H is simultaneously absorbed through the relation of B and H. It is shown that, with the help of this MIPML absorber, Berengers PML can be simply and successfully extended to arbitrary anisotropic magnetic media.

A stable algorithm for modeling lumped circuit source across multiple FDTD cells

Incorporating lumped-circuit elements into finite-difference time-domain (FDTD) simulation greatly enhances the FDTD methods capability to model both distributed structures and lumped circuitries. The multiple-cell formulation proposed by C.H. Durney et al. (see ibid., vol. 6, p. 85-7, Feb. 1996) is only numerically stable for modeling structures with large permittivity. A stable algorithm for modeling material with both large and small permittivity is presented in this letter. Verification data is given together with detailed derivations.

Accurate and detailed FDTD solution of microwave integrated circuits using the frequency shifting technique

By employing the elementary property (i.e., the frequency shifting technique) of the Fourier transform, a simple and efficient spectral estimation technique is developed. With this technique, extremely accurate and detailed frequency domain scattering parameters of general microwave integrated circuits can be obtained, without increasing any additional computation and programming efforts in the original FDTD simulation.