Channabasappa Eswarappa

One-way equation absorbing boundary conditions for 3-D TLM analysis of planar and quasi-planar structures

Absorbing boundary conditions based on one-way wave equations (formulated by Higdon for FD-TD analysis) have been investigated and implemented for the 3-D Symmetrical Condensed Node TLM analysis of dispersive microwave and millimeter-wave structures. Very low reflections over a wide frequency band have been obtained by concatenating two and three first-order boundary operators. Numerical stability of the absorbing boundary conditions with different discretizations of the boundary operators (derivatives) has been studied. It has been found that numerically stable algorithms can be obtained with proper discretizations. These excellent stable absorbing boundary conditions can considerably reduce the computational domain, thus making possible the 3-D TLM analysis of planar and quasi-planar structures with moderate computer resources. The scattering parameters computed using these boundary conditions for microstrip via holes and shorting pins compare well with the available data. >

Lumped element equivalent circuit parameter extraction of distributed microwave circuits via TLM simulation

A method for generation of lumped element equivalent circuits and the corresponding systems of ordinary differential equations for distributed microwave circuits is presented. Starting with a TLM analysis of a distributed multiport circuit the impulse response functions for reflection and transmission between the ports are computed. After Laplace-transforming the impulse functions numerically the poles are extracted within a specified domain of the complex frequency plane. From these poles canonical equivalent circuits representing the branches of the lumped element equivalent circuit are derived directly. By this way the topology as well as the parameters of the lumped element equivalent circuit are determined. The method is demonstrated in modeling of distributed one-port and multiport circuits.<<ETX>>

An alternative way of computing S-parameters via impulsive TLM analysis without using absorbing boundary conditions

This paper presents a transmission line matrix (TLM) procedure to compute wideband scattering parameters of microwave structures from a single time domain simulation without using matched loads or absorbing boundary conditions (ABCs) in the main propagating direction. This is done by computing the admittance parameters in the time domain through an impulsive excitation and short-circuit boundary conditions (SBCs). Results presented for both lossy and lossless cases agree well with available data. Also, this procedure does not require the prior knowledge of the propagation characteristics (such as incidence angle or effective dielectric constant) of the guide.<<ETX>>

Bridging the gap between TLM and FDTD

A real-time interface between transmission line modeling (TLM) and finite difference time domain (FDTD) algorithms has been developed and validated. A structure can be subdivided in an arbitrary manner into connected TLM and FDTD subdomains that are updated simultaneously. In this way the specific advantages of both methods can be exploited when solving a given problem. The interface procedure has been validated by solving identical structures, first with TLM, then FDTD, and finally with a combination of both. All three methods yield identical numerical results for equal excitation, space, and time resolution.

ABSORBING BOUNDARY CONDITIONS FOR TIME-DOMAIN TLM AND FDTD ANALYSIS OF ELECTROMAGNETIC STRUCTURES

Abstract In this paper, the absorbing boundary conditions (ABCs) most commonly used in time-domain numerical methods such as the Transmission Line Matrix (TLM) method and the Finite Difference Time Domain (FDTD) method are reviewed. Such boundary conditions are required to simulate matched loads and open surfaces. We discuss and compare ABCs based on single impulse reflection coefficients, one-way equations, diakoptics or Johns matrices, and Berenger‘s perfectly matched layer (PML). Even though the emphasis is on applications in the TLM method, the major differences in the performances of these ABCs in TLM and FDTD are pointed out. Two ways of applying ABCs in TLM (voltage impulses and node voltages) are discussed. It has been observed that an ABC applied directly to the TLM voltage impulses absorbs better than the same ABC applied to the TLM total node voltages or FDTD field values. Furthermore, different ways of stabilizing one–way equation ABCs, such as adding damping factors, choosing proper discretiz...

Efficient field-based CAD of microwave circuits on massively parallel processor computer using TLM and Prony's methods

This paper reports progress in the CAD of microwave circuits using a parallel TLM code with Pronys method. With only 100 TLM time samples, the scattering parameters of a microwave bandpass filter are extracted via Pronys method on a normal workstation. Such a combination of the parallel TLM module and Pronys method brings efficient optimization using time domain techniques within acceptable time limits.<<ETX>>

Time domain analysis of via holes and shorting pins in microstrip using 3-D SCN TLM

The scattering parameters of microstrip via holes and shorting pins are computed using the 3-D SCN (symmetrical condensed node) TLM (transmission line matrix) method. The results agree well with the available data at low frequencies, thus demonstrating that the TLM method is a powerful tool applicable in the analysis of monolithic microwave integrated circuits of high-density and high-speed digital microwave circuits.<<ETX>>

Performance study of one-way absorbing boundary equations in 3D TLM for dispersive guiding structures

Several absorbing boundary conditions (ABCs) based on one-way wave equations (mostly applied to the finite-difference-time-domain method) have been studied and adapted for the 3D symmetrical condensed node analysis of guiding structures. The ABC based on perfect absorption of waves at two incident angles has given superior results when compared to other absorbing boundaries. Reflections less than 2% over a large frequency spectrum have been obtained for dispersive structures like microstrip and finlines. These excellent ABCs can considerably reduce the computational domain, thus making possible the 3D TLM (transmission line matrix) analysis of planar and quasi-planar structures with moderate computer resources.<<ETX>>

Absorbing boundaries for 3D-TLM modelling of microstrip patch antennas

In this paper, a time domain 3D-TLM algorithm has been applied to analyze a microstrip patch antenna. A proper treatment of absorbing boundaries is presented for accurate analysis of radiating structures. The results obtained for a rectangular patch microstrip antenna compare well with available data.

Periodic filters for performance enhancement of millimeter-wave microstrip antenna arrays

In this paper, periodic filters have been employed to enhance the performance of microstrip antenna arrays in automotive radar sensors. An isolation of more than 45 dB has been measured between transmit and receive antenna arrays formed on the same substrate with a separation distance of only 40 mm between them. The isolation enhancement obtained is more than 15 dB. Also a gain enhancement of about 2 dB has been observed due to employment of these periodic filters. Since these periodic filters consist of circular openings etched on the ground plane of the antenna, there is no additional cost or fabrication effort associated with this technique. These openings act as periodic stop band filters to suppress surface waves propagating between the antenna arrays. Measured and computed isolation values agree well.