Lossy Transmission Line Model Research Articles

Time-domain Analysis of Traveling Wave Switches based on Time-variant Transmission Line Model

Background and Objectives: Switches play an important role in controlling the signal flow in telecommunication systems. The traveling wave switch structure is introduced based on active transmission lines. By applying the gate voltage (Vg), the transfer of signal through the drain transmission line is controlled. By increasing operating frequency, lumped model is unreliable and semi and fully distributed modeling should be applied for the analysis of these elements. Methods: Traveling wave switches can be analyzed based on the lossy transmission line model, in linear and non-linear modes in the time and frequency domains. The study of transient behavior and time domain response of switch is very important. Switching and transient from on to off state and vice versa affect the performance of telecommunication systems.In the proposed method, the switch is modeled as the lossy transmission line that the primary elements of this model change with time based on the control voltage applied to the gate and are considered as variable with time. The structure is discretized in the space and time domains with ∆z and ∆t steps. The Finite-difference time-domain (FDTD) method is utilized to study the transient response of switches. By using the leap-frog algorithm, the new voltages and currents of the transmission line are calculated based on the values of adjacent spatial and temporal steps.Results: The transient response of the switch is analyzed in transition from off to on states and vice versa, for the 800µm switch at 60GHz, based on the parameters of the passive transmission line and nonlinear Curtice2 FET model.Conclusion: For transient analysis of the structure, the time-variant lossy transmission line model was used that its elements changed based on the applied control voltage. The results of FDTD method were investigated with the transient analysis of commercial software that show good agreement with each other and validated the proposed method.

A Lossy Transmission Line Model for the Scan Impedance of the Infinite Dipole Array

In this paper, an analytical formulation of the infinite dipole array scan impedance is presented. The primary contribution of this work is the introduction of a lossy transmission line analogue which simultaneously models the Floquet modal impedances as well as the reactive properties of the dipolefs physical geometry. A scan dependent line inductance is implemented, resulting in accurate impedance predictions at extreme scan angles. The model accurately predicts the input scan impedance of tightly-coupled arrays and connected arrays for a variety of element geometries. Ground planes, substrates, superstrates, and feed structures are also incorporated in the model. Calculated impedances are compared to full-wave electromagnetic models, demonstrating high accuracy predictions from broadside to near 90. in each scan plane. Finally, an array which scans to 60. in each scan plane is rapidly optimized using only the transmission line model and compared to full-wave simulations, achieving a 3:1 VSWR over a 6.1:1 bandwidth, demonstrating the value of the model as a starting point for array design.

Approach to modelling uniform transmission lines for broadband high‐frequency applications

A novel high-frequency lossy uniform transmission line model is presented in this study. Novel features include a compactness of form and a level of simplicity that confers enhanced simulation efficiency in practical applications. Although specifically developed to target implementation in generic versions of SPICE, the compact high-frequency model can be implemented using only four lines of netlist syntax in the case of circuit simulators that offer native Laplace equation support. Featuring a broadband frequency response characteristic that is defined by only four parameters, the compact HF model is based on a novel theoretical approach that elegantly connects the four model parameters to physical line parameters using only elementary line characterisation data. Important and perhaps surprising differences between the new model theory and classical textbook theory are highlighted and discussed. The lessons learned are then incorporated into a second hybrid model featuring a higher level of complexity that combines both new and classical theoretical approaches into a single set of model equations that are better suited for atypically small controlled impedance structures such as silicon interposers and on-chip clock and data distribution schemes.

Time-Domain Procedures for Lightning-Induced Voltage Calculation in Electromagnetic Transient Simulators

In this paper, two time-domain procedures are proposed for the calculation of lightning-induced voltages using lossy transmission line models available in electromagnetic transient simulators. In both procedures, the influence of the incident electromagnetic field is represented in the form of current sources that are connected externally at the ends of the illuminated line. One of the procedures is formulated directly in the phase-domain and is compatible with the universal line model (ULM). The second procedure is formulated in the modal domain and is compatible with the transmission line model proposed by Marti. Both procedures are validated taking as reference a first order FDTD solution of telegrapher's equations considering the presence of external electromagnetic fields. It is shown that the proposed procedures can be efficiently and accurately used for the calculation of lightning-induced voltages on overhead lines.

Research and validation of design principles for PVDF wideband ultrasonic transducers based on an equivalent circuit model

With the increasing use of ultrasonic measurement technology in many fields, the demand for the wideband ultrasonic transducers is also growing. In order to design a wideband piezoelectric ultrasonic transducer, the design principles of wideband PVDF piezoelectric ultrasonic transducers are studied in this paper. A new equivalent circuit model of piezoelectric ultrasonic transducer is used here to simulate the piezoelectric ultrasonic transducer, which combines with the controlled source model and the lossy transmission line model. Based on this model, the relationships between physical structures and properties of PVDF transducers are studied both in simulation and experiment. It shows that the center frequency and many other property parameters of PVDF ultrasonic transducers are strongly related to the physical structures of it. Finally, a wideband PVDF piezoelectric ultrasonic transducer is produced with the center frequency of about 5.3 MHz ± 0.1 MHz and the bandwidth of more than 90%.

An Efficient Approximation Method for Delay-Rational Model of Multiconductor Transmission Lines

In this paper, a new algorithm for the generation of the approximate poles and residues of multiconductor transmission lines (TLs) characterized by frequency-dependent per-unit-length parameters is presented. By using the Green’s function-based delay-rational model for lossy TLs, the proposed algorithm can calculate a reduced number of rational functions to enhance computational efficiency. Also, it can further improve the efficiency by performing the approximation of poles and residues instead of solving high-order equations. The preservation of passivity proof is developed. The frequency response and transient analysis results are presented and compared to those of the delay-rational model. The outcomes show that the proposed method can significantly improve the speed while preserving a similar accuracy.

A Generalized Lossy Transmission-Line Model for Tunable Graphene-Based Transmission Lines with Attenuation Phenomenon.

To investigate the frequency shift phenomenon by inserting graphene, a generalized lossy transmission-line model and the related electrical parameter-extraction theory are proposed in this paper. Three kinds of graphene-based transmission lines with attenuation phenomenon including microstrip line, double-side parallel strip line, and uniplanar coplanar waveguide are analyzed under the common conditions where different chemical potentials are loaded on graphene. The values of attenuation constant and phase constant, and the real and imaginary parts of the characteristic impedance of transmission lines are extracted to analyze in details. When the attenuation constant and the reactance part of the characteristic impedance are approximately equal to zero, this kind of transmission line has low or zero insertion loss. On the contrary, the transmission line is under the radiation mode with obvious insertion loss. The phase constant changes linearly under the transmission mode and can be varied with changing of chemical potentials which attributes to the property of frequency tunability. Furthermore, a bandwidth reconfigurable uniplanar coplanar waveguide power divider is simulated to demonstrate that this theory can be applied to the design of three-port devices. In summary, this work provides a strong potential approach and design theory to help design other kinds of terahertz and mid-infrared reconfigurable devices.

Transmission-Line Model of Nonuniform Leaky-Wave Antennas

Nonuniform leaky-wave antennas (LWAs) are analyzed and synthesized using a lossy transmission line model. The analysis is based on a general waveguide circuit theory. Compared to the classical approach, the model yields a higher accuracy in the computation of both aperture field distribution and radiation patterns. The proposed analysis is also able to provide scattering parameters of the whole structure in a fraction of a second, which is valuable for antenna optimization. Based on the analysis, a general method for far-field pattern synthesis utilizing global optimization is presented. As an application demonstration, the half-mode substrate-integrated waveguide (HMSIW), or half-width microstrip line, has been selected as basis structure for the LWA designs. Two antennas have been optimized targeting different specifications, i.e., a low-sidelobe level and a wide null in the radiation pattern. Experimental results are provided for these selected examples of nonuniform LWAs, which ultimately validate the proposed technique as an improvement over the classical approach.

Surface acoustic wave generation and detection using graphene interdigitated transducers on lithium niobate

We demonstrate the feasibility of using graphene as a conductive electrode for the generation and detection of surface acoustic waves at 100 s of MHz on a lithium niobate substrate. The graphene interdigitated transducers (IDTs) show sensitivity to doping and temperature, and the characteristics of the IDTs are discussed in the context of a lossy transmission line model.

Electromagnetic Absorption Rate in a Multilayer Human Tissue Model Exposed to Base-Station Radiation Using Transmission Line Analysis

As the wireless communications have recently expanded, the potential effects on human body of electromagnetic (EM) fields produced by the base-station antennas has become of great concern to people especially living near the exclusion zone of the antennas. This letter presents the simulation of an electromagnetic radiation exposure and the calculation of specific absorption rate (SAR) and temperature variation for a multilayer human tissue model. The fact that field equations for planar wave propagation are analog to the circuit equations for a wave on a transmission line is exploited to use the lossy transmission line models of the ORCAD PSpice simulator. Exposure simulations are carried out considering a distance of 10 m between a base-station antenna and a multilayer human tissue model for exemplary frequencies of 915 and 2450 MHz. To the authors' knowledge, it is the first time PSPICE has been used for SAR and related temperature rise calculation.

A didactically novel derivation of the telegraph equation to describe sound propagation in rigid tubes

Starting from first principles, we derive the telegraph equation to describe the propagation of sound waves in rigid tubes by using a simple approach that yields a lossy transmission line model with frequency-independent parameters. The approach is novel in the sense that it has not been found in the literature or textbooks. To derive the lossy acoustic telegraph equation from the lossless wave equation, we need only to relax the assumption that the dynamical variables are constant over the entire cross-sectional area of the tube. In this paper, we do this by introducing a relatively narrow boundary layer at the wall of the tube, over which the dynamical variables decrease linearly from the constant value to zero. This allows us to make very simple corrections to the lossless case, and to express them in terms of two parameters, namely the viscous diffusion time constant and the thermal diffusion time constant. The coefficients of the resulting telegraph equation are frequency-independent. A comparison with the telegraph equation for the electrical transmission line establishes precise relationships between the electrical circuit elements and the physical properties of the fluid. These relationships are thus proven a posteriori rather than asserted a priori. In this way, we arrive at an instructive and useful derivation of the acoustic telegraph equation, which takes viscous damping and thermal dissipation into account, and is accessible to students at the undergraduate level. This derivation does not resort to the combined heavy machinery of fluid dynamics and thermodynamics, does not assume that the waveforms are sinusoidal, and does not assume any particular cross-sectional shape of the tube. Surprisingly, we have been unable to find a comparable treatment in the standard introductory physics and acoustics texts, or in the literature.

Improved Reliability and Functionality of Clock Networks in ULSI Devices Due to Lossy Transmission Line Modeling Method

In this paper, the ways to improve the functionality and reliability of Digital Signal Processors, used to support optical networks, have been studied. Specifically, supported on our finding from previous experimental studies that on-die global interconnects should be described by a distributed RLC model, we propose to model shielded lines, carrying the most critical signals, by a Lossy Transmission Line (LTRA) model. The proposed method obviates the need for tedious simulations, which also due to many inevitably required oversimplifications have a low correlation with a real circuit behavior. The SPICE simulated signal waveforms obtained at the far-end of shielded lines correlate well with experimentally measured waveforms within a typical 45 nm CMOS technology ULSI chip. Based on both, simulations and experimental measurements, we have construed criteria whereby we modified the CMOS driver strength selection guideline to conform to the distributed nature of on-die interconnection lines. The performed simulations on a multi-level clock H-tree structure from a high-performance core block indicate that the new approach considerably improves MOSFETs reliability and power dissipation.

A distributed transmission line model of cloud-to-ground lightning return stroke: Model verification, return stroke velocity, unmeasured currents and radiated fields

Among the various models for lightning return strokes (LRS) that exist, the lossy distributed transmission line (DLCR) model, it is shown herein, is a dependable, comprehensive and accurate model. The model contains inductance (L), capacitance (C), and the heat-loss resistance (R). Recently, many alternative models have been proposed, and the adequacy of the DLCR model (DLCRM) has been questioned because of some shortcomings in the previously reported DLCRM simulation results. This paper corrects some of these shortcomings, such as correct representation and computation of the LRS current pulse wavefront, and the special nature of the attachment point at the earth end. In this paper where the DLCRM model proposed is a self-consistent model, within the assumptions stated and justified, it is shown that the LRS velocity predicted by the DLCRM is about fifty to seventy percent less than the velocity of light (for example, c/3). The velocity determined from the DLCRM presented here agrees with the measured LRS velocity, and captures also the drop in velocity as the LRS moves away from the segments away from the ground. When considering both the physical principles and observations of the earth flash lightning return stroke (LRS), the DLCRM yields results that are consistent with lightning measurements. The DLCRM may be used to obtain important engineering parameters which are not easily measured; one such example is the very high rate of rise of currents on a submicrosecond timescale (for example, 98 kA/μs), whereas the microsecond rate of rise of current may be a tenth of the submicrosecond values. Relating the computed electric and magnetic fields radiated by the LRS currents obtained from the DLCRM shows the correlation between the LRS current waveforms and the electromagnetic field waveforms at different distances from the LRS channel. Moreover, for unbranched first and subsequent return strokes, the model’s electrical parameters such as inductance (L), capacitance (C) and resistance (R) values may be calculated from basic principles, with the assumptions made clearly defined and justified. Among the various models for lightning return strokes, the lossy transmission line model (the DLCRM) remains the most dependable when considering both the physical principles and measurements that provide a consistent and self-contained justification for the LCR model. Key words: Lightning return stroke, transmission line model, lightning rate of rise of current, lightning radiated electromagnetic fields.

Modelling and optimum design of ultrasonic transducer for therapy application

In ultrasound imaging applications, transducers with high sensitivity, good impulse response, low-ripple, and wide-band performance are desired. Widening the bandwidth of transducers by introducing quarter-wavelength matching layers on the piezoelectric ceramic may result in a reduction in power transmission and sensitivity. For therapy, it is more important to have high-transmitting power than to have wide-bandwidth characteristics. Since a 15% bandwidth is sufficient for therapy applications, a matching-layer thickness that is a little bit shorter or longer than one-quarter wavelength is proposed as a good trade-off between the two criteria. By tuning the thickness and acoustical impedance of the matching layer, transducers with optimum bandwidth and transmitting power can be obtained. An acoustical lossy transmission line model for an ultrasonic transducer is proposed. Then, the developed model is implemented on PSPICE-controlled source programming technology to precisely predict the performance of the transducer's characteristics. Good agreement between the simulation results and experimental results has been achieved.

Study of a large-area THz antenna by using a finite difference time domain method and lossy transmission line

Large-area THz antennas are studied by using a finite difference time domain method and a lossy transmission line model. The temporal evolution of an emitted pulse from a specified antenna is experimentally realized, the result is compared with the numerical result and good agreement is observed. The effect of the laser beam spot size, carrier life-time and collision time on temporal evolution of a THz pulse is investigated using this technique.

Currents in buried grounding strips connected to communication tower legs during lightning strikes

During a lightning strike to communication tower stroke currents are shared by the tower and by the shields of the cables along the tower. The currents in the tower proceed towards the grounding system (possibly a combination of counterpoises or ring conductors or ground rods or grounding grids) connected to tower legs' foundation. In this paper, lightning strike to communication tower on mount Gaisberg in Austria is considered and measured currents at the tower top and those shared by an instrumented grounding strip connected to one of the tower leg's are presented. The measured currents at different locations on the 70-m long ground strip are compared with the predictions of a frequency dependant lossy transmission line (TL) model and reasonably good agreement was found. From this validation it is claimed that the TL models are appropriate for lightning transient analysis of grounding systems.

Distributed Lumped Loads and Lossy Transmission Line Model for Wideband Spiral Antenna Miniaturization and Characterization

A lossy transmission-line model that incorporates the radiation resistance of small loop antennas is introduced to characterize the input impedance of a spiral antenna over a large frequency range. This model also leads to a concept of controlling the current velocity and impedance on a spiral antenna by introducing distributed reactive loading along the spiral arms. An important application of the concept is to reduce antenna size and this is demonstrated by numerical simulation examples.

Theoretical and Experimental Investigation on PCB Helix Antenna

A method to modify the PCB helix frequency offset aroused by the irregular PCB shape and dielectric constant εr is proposed; then a broadband antenna design employing nonuniform pitch is introduced; finally a lossy transmission line model is presented to analyze antenna gain affected by the lossy PCB dielectric, the accuracy of the model is verified by comparison with results of a rigorous theory and experiment.

Theoretical and experimental analysis of current spreading in AlGaInP light emitting diodes

The profile of light emission from aluminum gallium indium phosphide (AlGaInP) light emitting diodes has been studied and compared with the theoretical modeling of current spreading using a lossy transmission line model of current injected into the active region. Discrepancies between the experimentally determined emission profile and the theoretically predicted current injected into the active region have been analyzed and explained using a Monte Carlo ray tracing simulation which considers the trajectories of the photons after leaving the active region and the particular geometry of the device current, die size, and current spreading layer resistance upon the emitted emission profile. The combination of the current spreading and ray tracing models give very good agreement with the experimental emission profiles for both thin and thick current spreading layers.

Monte-Carlo based simulation of surface light emission profiles from AlGaInP light emitting diodes

Light emission profiles from AlGaInP LEDs are compared with those obtained via Monte-Carlo simulation and a lossy transmission line model. Results show good agreement for devices with thin current spreading layers. However, for thicker layers, geometric effects dominate the output profile, resulting in discrepancies between experimental data and the transmission line model. The simulation of emission profiles confirms this discrepancy, caused by light escaping from below the p-contact.