Impedance Of Dipole Research Articles

Characteristics of an electric dipole in a plane waveguide with an inhomogeneous filling in the long-line approximation

Within the framework of the long-line approximation, we obtain the expressions for the current distribution, input impedance, and admittance of a nonsymmetric thin electric dipole whose ends are connected to perfectly conducting walls of a plane waveguide filled by an inhomogeneous dielectric. The use of this approximation allows one to qualitatively interpret the results of rigorous solution of the problem of the effect of the medium inhomogeneity on the radiation characteristics of the antenna.

Calculation of the input impedance of dipoles in proximity to walls

The trend towards microcells is likely to result in more base station antennas being sited on the sides of buildings. However, the presence of the wall affects the antenna's input impedance. This contribution investigates the prediction of this detuning effect using a number of integral equation approaches. The reliability of different approaches is considered and two complex image-based formulations shown to be especially well suited to this situation are presented.

A simple closed‐form formula for the mutual impedance of dipoles

AbstractA simple and compact formula of dipole mutual impedance is presented. This method gives an analytical expression of mutual impedance between two real, thick center‐fed dipoles in a general geometrical configuration for small distances. The results of this new formulation show a good agreement with the numerical (NEC‐2) and experimental results. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 371–374, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10465

Radiation Impedances of Bent Dipoles near a Perfectly Conducting Sphere

Radiation Impedances of Bent Dipoles near a Perfectly Conducting Sphere

Broadband calculable dipole reference antennas

A broadband calculable standard dipole antenna has been developed, with an uncertainty in the antenna factor (AF) of better than /spl plusmn/0.15 dB at the resonant frequency, f/sub res/, in the frequency range 30 to 500 MHz and /spl plusmn/0.2 dB in the range 600 MHz to 1 GHz. For broadband operation of the dipole resonant at 60 MHz the uncertainty is /spl plusmn/0.2 dB over a range 0.33 f/sub res/ to 1.83 f/sub res/. These uncertainties have been validated by close agreement of the measured insertion loss between dipole antennas above a conducting ground plane, with the loss predicted by analytical and numerical methods. The AF measured by the two-antenna method also agrees with the calculated AF. The technique was applied to reference monopole antennas for which AF was determined to an uncertainty of /spl plusmn/0.2 dB over the frequency range 10-100 MHz. The key achievements are: the construction of a very large and flat ground plane, validation of numerical versus analytical calculations of impedance and effective length of resonant dipoles, excellent agreement between measurements and method-of-moments calculations of the coupling between resonant dipoles, good agreement over a broad bandwidth, careful design of antennas and supports, and precision measurements.

Enhanced Z-mode radiation from a dipole

An HF transmitter and synchronized receiver both connected to dipoles were operated during the tethered experiment OEDIPUS C. On the flight down leg after the tether had been cut, direct bistatic propagation experiments were made with the transmitter in one subpayload and the receiver in the other subpayload. Medium-frequency Z-mode transmissions were observed to be strong compared to the adjoining wave modes. This Z-mode is the left-hand polarized mode propagating between its cut-off frequency f Z =(− f c +( f c 2+4 f p 2) 1/2)/2 and the local plasma frequency f p ; f c is the local gyrofrequency. It is of particular theoretical interest because its refractive index surface evolves from a simple ellipsoid to an ellipsoid with inflections as frequency is swept through the band. The Z-mode signal was strongest at frequencies just below f p , at relatively low f p values. When f p increased, the Z-mode signals were strongest at frequencies just above f Z. Details of these characteristics are presented. A possible explanation is that the transmitting dipole impedance in this frequency range provides a better match to the output of the transmitter than in other wave modes swept.

Unusual method for impedance evaluation of short dipole with arbitrarily mutual arms location and the implications for dc field sensors

A relatively unknown analytical method is developed further in order to evaluate the capacitance between two long cylinders of equal length and diameter. The main approximation associated with the relatively unknown method was in assuming that the cylinders are uniformly charged no matter what is their length and diameter and no matter what is their mutual location and orientation. The cylinders in our treatment are long in terms of length to diameter ratio, but they are much shorter than a wavelength. One of the presently treated cases is due to two gapped collinear cylinders of equal diameters and lengths. Such a structure (when the gap between the cylinders is small) is similar to that of a short dipole antenna. There have been several analytical methods mentioned in the literature for estimating the short dipole impedance. It is interesting that the present method of evaluation, which is completely independent, compliments some of the previous methods. It is also known relatively well that evaluating the inductance of iron cored coils bears direct relationship (through EM duality theory) to the short electric dipole capacitance evaluation. It means that the present work is helpful for inductors design and also for evaluating cored search coil magnetometers. The work contributes to better understanding of fieldmills and fluxgates that are employed for sensing electric and magnetic dc fields, respectively. Furthermore, a new type of an electric dc field sensor has been developed by us recently. Its structure is that of a short dipole, where the length of the gap between the dipole cylindrical arms is modulated periodically. Its operation is somewhat similar to that of a fieldmill, and is also due to the periodic variation of the structure antenna-capacitance. The presently developed analytical method serves also for evaluating the variable capacitance of the new sensor, and is in particular helpful for the interpretation of its operation. Generally speaking, the work is helpful in demonstrating that dc field sensors should be regarded as being related to antennas and should not be treated as if they were separate entities.

Resonance excitation of a radially oriented coupled impedance dipole

Resonance excitation of a radially oriented coupled impedance dipole

HORIZONTAL WIRE ANTENNA ABOVE LOSSY HALF-SPACE: SIMPLE ACCURATE IMAGE SOLUTION

A simple, approximate, but highly accurate, method is proposed for the analysis of horizontal thin-wire antennas above a lossy half-space. In the first step, the contribution of the lossy half-space to the field of a horizontal Hertzian dipole above the interface, both in the half-space above and in that below the interface, is approximated by the field of few (typically six) equivalent sources (images). The relative image intensities are obtained by enforcing the boundary conditions for the tangential components of the electric and magnetic field at a number of points at the interface. The field of the images is introduced into the Hallen equation; current distribution is approximated by polynomials and determined by point-matching. The results for the impedance of horizontal dipoles obtained by the present method are in excellent agreement with the exact results (obtained from the Sommerfeld theory), although the proposed method is conceptually much simpler and requires at least an order of magnitude less computing time than the exact method.

The impedance of a center-fed strip dipole by the Poynting vector method

The impedance of a center-fed strip dipole of width w and thickness t, with t/spl Lt/w, is obtained by the Poynting vector method. With w also taken to be small with respect to the operating wavelength (w/spl Lt//spl lambda/) the surface current on the dipole is modeled by the classical sinusoidal standing wave along its length. There are, however, appropriate transverse singularities assumed at the edges of the strip. The Poynting vector method leads to a two-dimensional integral in the transverse coordinates involving the classical mutual impedance between filamentary dipoles located on the surface of the strip itself as well as the above mentioned transverse edge singularities. A Legendre series expansion of this mutual impedance (the coefficients obtained by numerical integration) leads to a rapidly convergent series solution (eight terms) for the overall impedance of the strip dipole. Numerical results are provided For a variety of strip widths, thicknesses and lengths. They are compared with the impedances of equivalent circular dipoles of radius a=(w+t)/4 and good agreement occurs except for quite wide strips (w=0.05/spl lambda/).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The input impedance of a thin dipole with sinusoidal surface current distribution by the Poynting vector method

The input impedance of a thin (a/spl Lt//spl lambda/) center-fed dipole with an assumed sinusoidal surface current distribution is obtained by the Poynting vector method. It is shown that by retaining the surface current distribution rather than replacing it by the classical equivalent line current on the dipole axis, the Poynting vector method can be used in a straightforward way and the dipole impedance obtained as a series in powers of ka. The series is appropriately truncated to order (ka)/sup 2/ since it is assumed that the dipole is thin (ka/spl Lt/1).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Moment method analysis of infinite stripline-fed tapered slot antenna arrays with a ground plane

A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described. The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas. Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method. Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays. Catastrophic effects such as scan blindness are accurately predicted. A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented. >

Millimeter-wave integrated-horn antenna. II. Experiment

For pt.I see ibid., vol.39, no.11, p.1575-81 (1991). The impedance and radiation patterns of a dipole-fed horn antenna in a ground plane are experimentally investigated at microwave and millimeter-wave frequencies. The agreement with the full-wave analysis technique presented in part I is good. The results indicate that for a 70 degrees flare-angle horn, horn apertures from 1.0 lambda -square to 1.5 lambda -square with dipole positions between 0.36 and 0.55 lambda yield good radiation patterns with a gain of 10-13 dB a cross-polarization level lower than -20 dB, and resonant dipole impedances between 40 Omega and 120 Omega . It is also found that the impedance measurements can be safely used for 2-D horn arrays, but the radiation patterns differ because of the Floquet modes associated with the array environment. The integrated horn antenna is a high-efficiency antenna suitable for applications in millimeter-wave imaging systems, remote-sensing, and radioastronomy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dipole impedance of a conducting cylindrical pipe with a discontinuous cross section

The problem of a charged particle traveling off-axis along a semi-infinite pipe within an infinite pipe is analyzed in the frequency domain and explicitly solved by means of Wiener-Hopf techniques for the dipole term. The method can be used to compute any m-pole component of the EM field. The formulas given for impedances (longitudinal and transverse) are valuable for a wide range of frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dipole impedance of a conducting cylindrical pipe with a discontinuous cross section

The problem of a charged particle traveling off-axis along a semi-infinite pipe within an infinite pipe is analyzed in the frequency domain and explicitly solved by means of Wiener-Hopf techniques for the dipole term. The method can be used to compute any m-pole component of the EM field. The formulas given for impedances (longitudinal and transverse) are valuable for a wide range of frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

PRINTED DIPOLE CHARACTERISTICS IN A TWO-LAYER GEOMETRY WITH UNIAXIAL ANISOTROPY

ABSTRACT The characteristics of printed antennas in a two-layer anisotropic substrate are investigated. This includes input impedance of a ceneter-fed dipole, radiation efficiency, antenna gain and radiation patterns. The analysis adopts the moment method solution of the integral equation where various numerical techniques are applied to enhance the computational efficiency. The effects of substrate and superstrate anisotropy on the antenna characteristics are also described.

Simple examples of the method of moments in electromagnetics

Three simple examples of the use of the method of moments in electromagnetics, i.e. analysis of the input impedance of a short dipole, and plane-wave scattering from both a short dipole and two coupled short dipoles, are presented. The relative simplicity of the examples is a direct result of obtaining simple expressions for the elements in the method-of-moments impedance matrix.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A method for synthesis of small arrays of printed dipole antennas backed by a ground plane

A method is proposed for synthesis of antenna arrays consisting of narrow strip‐dipole antennas printed on a thin dielectric substrate. Approximately antiresonant dipoles (i.e., dipoles about one wavelength long) are considered, because by moderate variation of their width and length their impedance can be varied in a wide range. A method for analysis of such arrays is described first, in which the printed strip dipoles are replaced by approximately equivalent circular‐cylindrical dipoles with coaxial magnetic coating, using recently proposed generalization of equivalent radius of thin cylindrical antennas. An interactive optimization procedure is next applied for synthesis, which enables arrays to be obtained having array radiation pattern and, particularly, dipole impedances close to the desired.

Folded antenna loaded with a dipole for circular polarization

AbstractAnalysis and design of a circularly polarized antenna made of a folded antenna loaded orthogonally with a dipole of an appropriate length is presented here. This antenna is developed in recognition that a folded antenna includes the characteristics of a transmission line. It is a simple single‐feed antenna without a power divider and a phase shifter commonly used in a conventional crossed‐dipole antenna. Making use of the fact that the current distribution can be decomposed into the balanced and unbalanced modes, one can derive the equivalent circuit and the equivalent crossed dipoles of the present antenna. The circular polarization condition is derived on effective lengths and impedances of dipoles. Based on investigation of this condition, a circularly polarized antenna has actually been designed and the characteristics of axial ratio and radiation pattern have been obtained. It is found that this antenna has few structural restrictions. Among them, element length is somewhat arbitrary. Validity of the theoretical results has been experimentally confirmed.

Rigorous solution of a dipole antenna with lumped impedance loading

Hurd's Wiener–Hopf solution for the input impedance of long dipoles is extended to yield analytic expressions for the input admittance, current distribution, and far-field radiation pattern of a linear cylindrical dipole antenna symmetrically loaded with lumped impedances along its length. Results from this model provide a more accurate expression for the current distribution on an infinitely long dipole antenna than previously reported by Shen et al. and are in good agreement with reported experimental and theoretical data. The new expressions give a better insight into the concept of standing- and travelling-wave antennas as well as the difference between loading with passive and active loads.