Poman P. M. So

A two-dimensional transmission line matrix microwave field simulator using new concepts and procedures

A two-dimensional field simulator for microwave circuit modeling is described. It incorporates a number of recently developed concepts and advanced transmission line matrix (TLM) procedures. In particular, a discrete Greens function concept based on P.B. Johns and K. Akhlarzads time-domain diakoptics is realized, providing a high level of processing power through modularization of large structures at the field level, simulation of wideband matched loads or absorbing walls, modeling of frequency-dispersive boundaries in the time domain, and large-scale numerical preprocessing of passive structures. Nonlinear field modeling concepts are also implemented in the TLM field simulator. It can analyze two-dimensional circuits of arbitrary geometry containing both linear and nonlinear media. The circuit topology is input graphically. Both time-domain and frequency-domain responses can be computed and displayed. The capabilities and limitations of the simulator are discussed, and several microstrip and waveguide components are modeled to demonstrate its important features. >

The generation of optimal microwave topologies using time-domain field synthesis

We present a novel approach to the design of microwave structures using time-domain field synthesis. A standard transmission-line matrix (TLM) electromagnetic analysis of the starting geometry yields the structure response and the field distribution on the optimizable boundary parts. A number of characteristic frequencies equal to the number of designable parameters of the structure are determined first. For narrow-band structures, these frequencies may be natural resonance frequencies. For wide-band structures, we create appropriate resonance conditions. The target response of the structure allows us to identify the desirable values of these frequencies. For each parameter, a synthesis phase is then performed. In this phase, the optimizable boundary parts are replaced by matched TLM sources that inject sampled sinusoidal streams at the desired characteristic frequency. The TLM field model generates an electromagnetic field pattern. The synthesized geometry is obtained by examining the envelope of that field pattern. Our approach is illustrated by means of several examples.

The compensation of coarseness error in 2D TLM modeling of microwave structures

The origin of the coarseness error in two-dimensional TLM (transmission line matrix) meshes is investigated, and a method for compensating the coarseness effect without increasing the computational expenditure is presented. The coarseness error can be eliminated by modifying the properties of the nodes situated at sharp corners or edges. The compensation is achieved by adding reactive stubs to the corner nodes. As a result, relatively coarse TLM meshes may be used to obtain highly accurate results. The efficiency and accuracy of this method are demonstrated by comparison with analytically exact solutions. The savings in computational expenditure are typically three orders of magnitude in 2D-TLM simulations.<<ETX>>

New procedures for 2-D and 3-D microwave circuit analysis with the TLM method

Four contributions to numerical field modeling with the TLM (transmission line matrix) method are presented: (1) the formulation of a 3-D Johns matrix (or numerical Greens function) for wideband non-TEM (transverse electromagnetic)-absorbing boundary conditions using the 3-D condensed TLM node; (2) use of a tapered Johns matrix (or numerical Greens function) for improving the return loss of frequency dispersive absorbing boundaries; (3) a recursive algorithm for wideband non-TEM absorbing boundary modeling; and (4) a pseudoparallel iteration scheme for the simultaneous processing of TLM substructures. These procedures are essential for efficient time-domain modeling of 3-D waveguide discontinuities of arbitrary geometries. Their application saves considerable computer run-time and memory when compared with conventional TLM analysis.<<ETX>>

3-D TLM time domain electromagnetic wave simulator for microwave circuit modeling

A novel 3-D TLM (transmission line matrix) time domain simulator for electromagnetic waves in structures of arbitrary geometry is described. It computes their response to arbitrary excitation in 3-D space and time, and extracts their frequency characteristics via the discrete Fourier transform. It also visualizes the field propagation in a generated-solution mode (field animation). Furthermore it permits time reversal for inverse problem simulation. It has been implemented on RISC (reduced instruction set computer) workstations and 386 microcomputers.<<ETX>>

A general planar circuit simulator based on two-dimensional TLM method

A very user-friendly two-dimensional circuit simulator based on the TLM (transmission-line matrix) method (2D-TLM) has been developed. It can analyze two-dimensional circuits of arbitrary geometry containing both linear and nonlinear media. The circuit geometry is input graphically. Both time-domain and frequency-domain responses can be computed and visualized. As examples, a microstrip lowpass filter, a microstrip varactor multiplier, and a waveguide post-coupled filter have been analyzed and compared with other methods.<<ETX>>

Design and Implementation of MEFiSTo-2D Classic Plus

Transmission Line Matrix (TLM) and Finite Difference Time Domain are two similar computational electromagnetics (CEM) procedures. The former one is based on the Huygens’ Principle while the latter one is based on Maxwell’s Equations. In order to couple Ampere’s and Faraday’s laws via the discretized Maxwell’s Equations, the electric and magnetic field vectors in the FDTD mesh are staggered in space and time. This staggering arrangement is not needed in the TLM algorithm. As a result, TLM algorithms are simpler to implement than their FDTD counterparts. This chapter presents an overview of the two-dimensional shunt-node TLM procedure as well as the design and implementation of the TLM method in MEFiSTo-2D Classic Plus.

Time domain field synthesis with 3D symmetric condensed node TLM

A novel time domain field synthesis approach based on 3D symmetric condensed node TLM will be described. The field distribution on the designable boundary parts is determined through a traditional TLM analysis of a starting geometry. Designable parameters are associated with a set of characteristic frequencies of the structure. The desirable values of these frequencies are determined using design specifications in the form of an equivalent lumped element circuit. A synthesis phase is then carried out for each parameter, during which the associated boundary parts are replaced by matched sinusoidal sources with the desirable value of the associated characteristic frequency. The designable parameter value is determined by observing the envelope of the standing electric/magnetic field pattern.

CAD of E-plane circuits with field-theory based lookup tables and discontinuity models

A computer-aided design (CAD) procedure for E-plane circuits using field-theory-based lookup tables for the analysis of straight finline sections is reported. The lookup tables are generated with an accelerated spectral-domain program and interpolated with respect to frequency using physically realistic functions. This procedure reduces considerably the size of the lookup table, since only three frequency points are needed for each gapwidth. Interpolation with respect to the gapwidth is linear. Discontinuities are modeled using a combination of these lookup tables with closed-form expressions. All models have been implemented using the TOUCHSTONE SENIOR package, and thus take advantage of all capabilities inherent in this software. Agreement with measurements is good, but it is noted that this agreement ultimately depends on the accuracy of the models used.<<ETX>>