Wolfgang J. R. Hoefer

A Graded Mesh FD-TD Algorithm for Eigenvalue Problems

This paper describes the realization of a graded mesh for the FD-TD algorithm, and its application to three-dimensional eigenvalue problems. Eigenfrequencies of resonant structures can be obtained via Fourier transform exactly as with the uniform mesh FD-TD algorithm. However, the graded mesh leads to considerable CPU time reduction while its accuracy is comparable to that of the uniform mesh algorithm. Applications include planar and quasiplanar circuit structures.

Numerical Microwave Synthesis by Inversion of the TLM Process

In this paper, the principles of a novel TLM time domain synthesis procedure for microwave structures are presented. This procedure permits the reconstruction of primary and induced sources from their radiated fields in space and time by reversing the TLM time stepping process. The ability to reconstruct induced sources implies that the topology of discontinuities and scatterers in the field space can be determined from the full knowledge of the incident and the scattered fields, thus opening the way to numerical field synthesis of microwave structures as an alternative to synthesis by iterative optimization.

Stabilized 12 GHz MIC Oscillators using GaAs FET's

This paper describes low power oscillators principally intended for use in MIC mixer applications. The circuits are fabricated with Plessey GAT 3 and NEC (Nippon) V244 FETs suitably packaged for use with microstrip substrates. The oscillators have been stabilized using a TE012 cavity coupled to the microstrip through an aperture in the microstrip ground plane, or alternatively by means of a solid dielectric resonator on the surface of the substrate. Very good noise performance and temperature stability have been measured. The injection-locking behaviour of the oscillators has also been studied.

The numerical energy conservation of the TD-FD method

Numerical energy conservation property of the time domain-finite-difference (TD-FD) method is interpreted using a plane wave analysis. The basic algorithm of the TD-FD method is presented in order to help understand the analysis. Since the analysis is based on Von Neumanns approach, the stability inequality is also produced as another outcome. Application areas of the property are included. >

Empirical Analytical Expressions for Fin Line Design

This paper presents empirical expressions in closed form for the design of unilateral and bilateral fin lines. The guided wavelength and the characteristic impedance calculated with these expressions are accurate within typically /spl plusmn/ 2 percent of the values obtained using the spectral domain technique in the normalized frequency range: 0.35 /spl les/ b/lambda /spl les/ 0.70.

Optimal Waveguide to E-Plane Circuit Transitions with Binomial and Chebyshev Transformers

This paper presents closed-form expressions for the design of quarter-wave transformer sections for matching fin line tapers to their commensurate waveguide. The formulae have been derived using perturbation theory and homogeneous waveguide models. Measurements show that such transformers improve the return loss of transitions by more than 5 dB over a whole waveguide band.

New Horizons in Numerical Time Domain Modelling of Microwave Structures

In this paper, a number of new developments in time domain modelling of electromagnetic fields and their potential impact on computer-aided design of microwave circuits will be described. After a brief discussion of general field modelling issues, and a brief summary of Transmission Line Modelling (TLM) techniques, several novel TLM concepts and procedures which allow the modelling of frequency dispersive boundaries in the time domain, will be presented. They are opening new possibilities for the large-scale numerical preprocessing of substructures, the partitioning of large time domain problems at the field level, and for combining other numerical techniques with the TLM method. Finally, several applications of these concepts to microwave and millimeter wave CAD will be demonstrated, and some thoughts on the future evolution of field theory based design methods will conclude the paper.

Effect of dispersion in the 3-D condensed node TLM mesh

The general dispersion equation, derived for the 3-D transmission line matrix (TLM) condensed node mesh, is presented and compared to dispersion of the finite-difference time-domain and the expanded node TLM schemes. Spurious mode propagation, as predicted by the dispersion equation for the condensed node, is also addressed. Analysis of dispersive effects is essential to assessing abnormalities in time-domain simulations.<<ETX>>

New 3D TLM condensed node structures for improved simulation of conductor strips

The authors present a set of modified condensed node TLM (transmission line matrix) structures, compatible with the 3D TLM condensed node, that improve the modeling of conductor strips and provide a means of directly embedding lumped devices into the mesh. The improvement in accuracy is demonstrated by evaluating the propagation constant of a simulated microstrip line.<<ETX>>

A Contour Formula for Compensated Microstrip Steps and Open Ends

A formula for the contour of compensated microstrip steps and open ends is derived. Suitable for automated mask design, the expression generates an exponential transition minimizing the parasitic shunt capacitance and series inductance of microstrip step discontinuities.