Two-wire Transmission Line Research Articles

A simplified derivation of the capacitance of a two-wire transmission line

This paper demonstrates that it is much easier to determine capacitance in a two-wire transmission line by tracing a known line of force than by the methods which customarily have been used to solve this problem.

Organ dosimetry for human exposure to non-uniform 60-Hz magnetic fields

This work presents a realistic numerical evaluation of the currents induced by strong 60-Hz magnetic fields in the body of a power-utility worker in three configurations representative of live-line conductor/hardware maintenance tasks. Two postures involve a single-phase two-wire transmission line bundle. The third involves a more complicated three-phase conductor system in an underground vault. A current of 500 A is assumed in each conductor. The calculations employ a well-verified computer code applied to an anatomically derived heterogeneous conductivity model of the human body. The model voxel size (3.6-mm edges) is sufficiently high to resolve all major body components, as well as many smaller organs. The electric field and current density vectors associated with every voxel are calculated, permitting the computation of organ-specific dosimetric quantities such as spatial and temporal maximum and average values. For the two transmission line configurations, it is found that local peak values of the induced current density can exceed the commonly used standard threshold of 10 mAm/sup -2/ by a factor of up to 3-4, but the associated spatial averages do not exceed this threshold for any tissue. For the underground vault case, the spatial maxima in all tissues are below the threshold.

On the wide-band CW illumination of large-scale systems. II. The rhombic illuminator

The Phillips Laboratory has designed and constructed a continuous wave illuminator for studying the responses of large-scale systems subject to vertically or horizontally polarized electromagnetic stresses incident from the horizontal. The illuminator is developed by a nonuniform two-wire transmission line oriented over the system under test. When the wires are driven from a common mode voltage with respect to the ground a vertically polarized electric field is generated and when the wires are driven from equal but opposite voltages a horizontally polarized electric field is developed. The structure is called the rhombic illuminator since the wire configuration is very similar to the rhombic antenna. In order to illustrate the use of the illuminator, data are presented for the illumination field and for the response of an illuminated aircraft recorded at the Phillips Laboratory.

Polarization response of asymmetric-spiral infrared antennas

We present measurements on the polarization response of Ni-NiO-Ni diodes coupled to asymmetric spiral antennas. Our data are for the wavelength dependence of the orientation of the major axis of the polarization ellipse over the wavelength range 10.2-10.7 mum. The data are well fit by a two-wire antenna model. We find that the modes excited on the antenna are a combination of the balanced and unbalanced modes of a two-wire lossy transmission line.

Theoretical investigation of a free-electron maser operating with a TEM transmission line

The possibility of using the transverse electric magnetic (TEM) transmission line in free-electron masers (FEM) is discussed. It is shown that at the centimeter and long-millimeter wavelengths such transmission lines allow one to combine the advantages of an open cavity and a waveguide-based resonator. A particular case of an FEM-based on the use of a shielded two-wire transmission line is investigated theoretically. A mathematical approach that allows one to calculate transmission-line parameters important to the FEM application is developed. It is based on the use of the integral equation technique and on a new representation of the Green function of the internal region of a circle, which was obtained in this paper. Numerical analysis of effective mode area, wave impedance, and attenuation constant was made for the odd TEM mode, which is excited in FEM operation. The FEM under research at Tel Aviv University was considered as an example. The frequency dependence of gain for an FEM operating in the linear regime was calculated. That the obtained gain value is much higher than the ohmic losses in the transmission line shows the possibility of using the TEM transmission line in this FEM.

Electromagnetic analysis of a two-wire transmission line of parallel cylinders of unequal radii with dielectric coating

The paper presents a method for the evaluation of capacitance, characteristic impedance and velocity of propagation of a dielectric-coated two-wire transmission line of parallel cylinders of unequal radii under TEM mode approximation. A conformal transformation is used to transform the conductor and dielectric boundaries to appropriate contours extending over a fixed region along the imaginary axis in the transformed plane. Approximating the continuous curve obtained through transformation of dielectric boundaries by a very large number of discrete steps, the expression for the capacitance is derived in the form of a definite integral. Numerical data on capacitance, characteristic impedance, velocity of propagation in the absence and presence of a perfectly conducting ground plane are presented.

Analysis of a multilayered-metal thin-film transmission line

In this study, a perturbed-TEM analysis was conducted on a two-wire transmission line with a two-layered metal system that represents a typical metallurgy used in thin-film multichip modules (MCM's). Closed-form solutions were obtained for the current density, resistance, inductance, attenuation, and phase velocity. The proximity effects were clearly illustrated in the current density plots. It was shown that the increase in the attenuation and the resistance was caused by the skin effect and the power loss in the cladding conductor (copper line clad with 0.1-/spl mu/m thick chromium), and the increase (decrease) in the phase velocity (internal inductance) of the thin-film lines was caused by the penetration of the magnetic field into the conductors. >

Linear two-wire transmission line coupling to an external electromagnetic field. I. Theory

The telegrapher's equations have been derived electrodynamically for the transmission line of two linear parallel conductors separated by a dielectric layer and excited by an electromagnetic field. The line coupling to a plane electromagnetic wave is illustrated for an arbitrary orientation of Poynting's vector and various polarization angles. The results are compared with the ones of other papers. The role of the magnetic field, while exciting the line, is clarified. The equations obtained in the paper are solved analytically in the case of the line excitation source being an electromagnetic pulse of arbitrary form.

Radiation from the multibranching point of a transmission line

In this paper, branching configuration in a parallel two-wire transmission line is considered as the cause of the unwanted electromagnetic wave generation and the analysis and experiment are carried out on the radiation characteristics of the discontinuity. Understanding by a simple radiation mechanism is intended. The discontinuity of the traveling-wave current on the conductor of the transmission line is considered as the radiation source. By means of the principle of pattern multiplication, the expression of the radiation field from the junction of the transmission line is derived. It is shown that the reflection and transmission coefficient of the traveling wave at the branching point are important factors to determine the radiation pattern. Two types of branching line configurations are treated. One of them is a reflectionless configuration while the other is made of identical transmission lines. The radiation characteristics due to the difference of characteristic impedance are derived. It is shown that there are electric field components radiating strongly in the traveling direction of the current of the branching line and the one radiating strongly into the intermediate direction. By means of the experiment for a T branching line, the validity of the theoretical results is confirmed.

An analytic calculation of the interaction between a pulsed electromagnetic field and two-wire transmission lines in nonuniform media

A solution of the system of equations derived in [1] are obtained, and analytic expressions are found for the currents in a line with arbitrary input and output impedances. The results are compared with those obtained in other publications.

Theory of the interaction of a pulsed electromagnetic field with two-wire transmission lines in nonuniform media

Equations are obtained which describe the interaction between a nonstationary electromagnetic field and a measuring transducer consisting of two linear parallel conductors separated by a dielectric layer. The system of equations obtained holds for an arbitrary orientation of the Poynting vector and different angles of polarization.

End-effects in quasi-TEM transmission lines

Magnetostatic analysis of a finite-length two-wire transmission line yields simple closed-form expressions for inductive end-fringing and interaction between ends. A further argument relates the results to capacitive end effects. Application to microstrip-like lines, twin-strip line and coplanar waveguide is outlined. It is demonstrated by explanation and comparison with the literature that these effects are the dominant discontinuity elements in short lengths of line, vias, resonators, bends, and other basic microwave configurations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power deposition properties of a travelling-wave applicator for interstitial hyperthermia.

An interstitial hyperthermia applicator is described that is capable of providing uniform heating over an extended range of depths. The applicator utilizes glossy two-wire transmission lines that are terminated in p-i-n diodes that may be biased on or off. A pair of these transmission lines within a single applicator allows a variety of symmetrical and asymmetrical patterns to be produced. Theoretical predictions of the applicator's performance are provided that are based on empirically determined transmission line characteristics.

The analysis of the magnetostatic fields surrounding a twisted-pair transmission line using integral methods

An integral formulation is derived from the Biot-Savart law in conjunction with Gaussian numerical integral methods and applied to the computation of magnetic fields surrounding a two-wire twisted-pair transmission line in the static case. The results show the effects of the length of the pitch of the twisted-pair line on magnetic fields surrounding these lines and the 3-D nature of this field. It appears that, to obtain uniform heating, one should try different shapes for the exciting coils. Increasing the length of the heating coils improves the uniformity near the center of the workpiece, but has the effect of overheating at the edges. Changing the distance between the coils or the supply frequency does not have a significant effect on the heating pattern. The significance of the analysis lies in its relation to electromagnetic compatibility considerations which must be taken into account in the design of the electric power transmission and distribution system of NASA's Space Station Freedom (SSF). >

A finite-element ballooning model for 2D eddy current open boundary problems for aerospace applications

A combined finite-element (FE) ballooning method is described for electromagnetic field problems in 2-D cases with open boundaries, in which eddy currents may exist everywhere, including the exterior ballooning region. Solutions using this combined 2-D-FE ballooning model are shown to be in close agreement with analytical solutions for a simple eddy current example with an open boundary. The method is applied to the computation of fields surrounding two-wire parallel-pair transmission lines, one with a magnetic shielding and one with a conductive shielding. Quantification of such leakage fields surrounding aerospace power transmission system components is of importance in space station electromagnetic compatibility considerations. >

On the coupling of microwave radiation to wire structures

The general aspects of the excitation of wire structures under microwave illumination are presented and discussed. Numerical, analytical and experimental results are provided. A simple procedure is presented for bounding the response of certain canonical configurations. Results are obtained for a terminated single wire over a ground plane and for a two-wire transmission line under plane wave illumination. The variation of the induced current with the dimensions and frequency is considered. It is shown that the TEM (transverse electromagnetic) mode current is a suitable approximation for the wire current with line separations up to and exceeding a wavelength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Double-layer microstrip structures—lumped capacitances and open-circuit end correction

The analysis is reported of the lumped capacitance and open-circuit end effects of finite-length strip conductors in double-layer microstrip structures. Two specific configurations, namely double-layer microstrip and microstrip-with-overlay configurations, are considered. The analytical approach uses the variational technique in the Fourier transform domain in conjunction with the transverse transmission line technique. It is identified that the only parameter needed to analyse the lumped capacitances and open-circuit end effects of these microstrip structures is the admittance at the charge plane. This parameter can easily be determined from the two-wire transmission line equivalent circuit. Extensive numerical data are generated for the lumped capacitances and open-circuit end effects of the finite-length strip conductor in double-layer microstrip and microstrip-with-overlay configurations. The data presented should be useful in designing lumped elements and filters in these configurations.

Propagation along a two-wire line located at the air-Earth interface

A simple quasi-static expression for the propagation constant of a two-wire transmission line located at the air-Earth interface is derived. A numerical solution of the mode equation shows that the quasi-static approximation is valid when the wire separation is much less than a free-space wavelength. The quasi-static approximation can be used to determine the complex dielectric constant of the Earth from measurements of either the propagation constant or the characteristic impedance of the transmission line. >

On the suppression of asymmetric artifacts arising in an implementation of the thin-wire method of moments

The original version of the thin-wire frequency-domain moment-method program developed by J.H. Richmond (1974) has been modified to suppress the computation of nonphysical asymmetric fields. Richmond's implementation uses piecewise sinusoidal expansion and testing functions, along with filamentary current approximations. The modified version, termed the bridge-current version, is described. The original program and the modified version are compared with each other and with simplified theory, where applicable, on the following symmetrical structures: a rectangular wire loop, a two-wire transmission line, and a log-periodic dipole antenna. The bridge-current version is shown to eliminate the computation of nonphysical asymmetric fields, to be essentially invariant with respect to variations in segmentation for the above-mentioned structures, and to produce results that compare well with simplified theories where applicable. It is noted that the bridge-current version is particularly advantageous for structures that include close-spaced parallel wires connected by short wire segments. >

The influence of the external circuit on the ionization gauge stability

Parasitic rf oscillations, easily arising in Bayard Alpert gauges and also in other positive grid gauges, lead to some real and/or apparent variations of the gauge sensitivity. To study the influence of the external circuit on the grid current (at which oscillations arise) in the clear form, the two-wire air transmission line with movable short circuit was used as an external circuit. Changing the short circuit position, the onset of oscillations is moved to much higher emission currents. Even if any other method of oscillation dumping is used to improve the gauge stability, attention must be paid to the length of the supply leads. They should be of high-losses type and their lengths should be equal to or slightly smaller than an even multiple half of the wavelength.