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Diseño de un algoritmo de transformación de campo cercano a campo lejano en ambiente no reflectivo.
Abstract
Se desarrolla una herramienta computacional basada en el uso de fuentes equivalentes de corriente y el método de los momentos para la transformación de campo cercano - campo lejano, introduciendo innovaciones que permitan adaptar el método a un número mayor de tipo de antenas. Es necesario disponer de herramientas de cálculo computacional que permitan obtener el patrón de radiación a partir de datos de mediciones en zona de campo cercano, utilizando metodologías adecuadas de análisis que permitan determinar el valor del campo en cualquier punto, conociendo el módulo y la fase de los componentes tangenciales del campo en una superficie que envuelva a la fuente generadora. Para comprobar la validez del algoritmo, se proporcionan resultados de la aplicación de la herramienta a varios tipo de antenas lineales, construidos a partir de datos sintéticos en campo cercano, y el análisis comparativo de estos resultados con valores teóricos del patrón de radiación.
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Thesis (doctoral)--Technical University of Denmark, 1970.
Modern Antennas, 2nd edition provides a complete and rigorous treatment of the theory and practice of modern antenna design and use. Written by a team of experienced engineers, the text is presented in a simple and understandable manner which guides the reader progressively through the stages of the design process. The book is aimed at practising engineers and graduate-level students, and includes numerous examples of practical designs applied to real engineering situations. The second edition contains significant new material on antennas for mobile communications, and on signal processing antennas for applications in communications and radar. Written to serve the needs both of practising engineers and advanced and postgraduate students, Modern Antennas, 2nd edition is an essential handbook for any engineer involved in the field.
Aspects related to vector analysis and electromagnetic fields in free
space are examined, taking into account scalar and vector fields,
coordinate systems, differential elements of space, vector integration,
electric charges, electric and magnetic fields, and Maxwell's integral
relations for free space. Vector differential relations and Maxwell's
differential relations in free space are considered along with Maxwell's
equations and boundary conditions for material regions at rest, static
and quasi-static electric fields, static and quasi-static magnetic
fields, the Poynting theorem, a mode theory of waveguides, TEM waves on
two-conductor transmission lines, the analysis of reflective
transmission lines, and radiation from antennas in free space.
A series expression for the near-field radiation pattern of an aerial obtained with a directive measuring aerial in a two-dimensional system is derived from a cylindrical-mode expansion of the radiated field. Patterns calculated from this series show better agreement with experimental results at shorter ranges than is provided by previous series evaluations. An inversion of the first few terms of this series suggests a convenient technique for the determination of the radiation pattern from near-field measurements. Calculations based on this method of inversion indicate that the approximate shape of the pattern may be obtained with relatively little effort from the near-field pattern yielded by a small measuring aerial at a range of a2/¿, where a is the aperture length of the transmitting aerial. At ranges considerably shorter than a2/¿, a more directive measuring aerial, which provides a closer initial approximation to the far-field pattern, has the advantage of reducing the amount of calculation required.
A theoretical analysis of certain aerial problems is carried out with the help of the idea of a spectrum of plane waves introduced by Booker and Clemmow. The reciprocity theorem, which relates the behaviour of an aerial used for reception to the properties of the same aerial as a transmitter, is used to derive an expression for the power received by one aerial as a result of transmission from a second aerial at any distance from the first. It is shown that under the conditions used in aerial measurements the size of the receiving aerial can influence the errors in measured radiation patterns and power gains. In particular, the side-lobe levels obtained when too small a separation between the aerials is used can either be larger or smaller than the levels for the true radiation pattern. This result differs from that predicted by diffraction theory, which suggests that side-lobe levels measured at too small a distance are always worse than those in the true radiation pattern. Similarly, when the size of the receiving aerial is taken into account, errors in gain measurements are shown to be larger than those predicted by diffraction theory.
A new method is described of predicting an aerial radiation pattern from near-field measurements. The essence of this method is the expansion of the radiated field in terms of a series of radially expanding modes. The amplitude and phase of each mode are calculated by a Fourier analysis of the measured near field, and the radiation pattern is obtained as a Fourier series containing these measured amplitudes and phases. The theory is described in detail for a cylindrical (2-dimensional) aerial, and experimental results are presented to confirm the validity of this theory. The way in which the method may be extended to 3-dimensional aerials is explained. The method has the advantage that it can be applied anywhere in the near field
Ph.D. Demetrius T. Paris
The plane-wave spectrum concept is used to derive an expression for the radiation pattern of an antenna in a two-dimensional system and an investigation is made of the effect of the aperture size of the measuring antenna on the pattern obtained. It is shown that measured sidelobe levels either above or below the far-field values may be obtained. Measurements of near-field antenna radiation patterns are carried out in a parallel-plate pattern range, and the predicted effects of measuring antennas of finite size on the beamwidth and sidelobe levels of the measured patterns are confirmed experimentally.
We describe a technique for rigorously correcting for the effects of an arbitrary but known measuring antenna (or `probe¿) in determination of vectorial far-field antenna pattern and power-gain function from near-field measurements.
A method is presented for computing near- and far-field patterns
of an antenna from its near-field measurements taken over an arbitrary
geometry. This method utilizes near-field data to determine an
equivalent magnetic current source over a fictitious surface which
encompasses the antenna. This magnetic current, once determined, can be
used to ascertain the near and the far fields. This method demonstrates
that once the values of the electromagnetic field are known over an
arbitrary geometry, its values for any other region can be obtained. An
electric field integral equation is developed to relate the near fields
to the equivalent magnetic current. A moment method procedure is
employed to solve the integral equation by transforming it into a matrix
equation. A least squares solution via singular value decomposition is
used to solve the matrix equation. Computations with both synthetic and
experimental data, where the near field of several antenna
configurations are measured over various geometric surfaces, illustrate
the accuracy of this method
This paper presents a new approach to derive far-field data needed
in antenna and EMI/EMC testing from near-field measurements. An exact
integral equation solution to the wave propagation problem is used to
transform the near-field data to the far field. The method requires
near-field measurements on two closed surfaces enclosing all sources and
inhomogeneities. The approach is validated with numerical simulation of
measurements of fields radiated from a known antenna
A new technique that significantly minimizes the aliasing error encountered in the conventional use of the fast Fourier transform (FFT) algorithms for the efficient evaluation of Fourier transforms of spatially limited functions (such as those that occur in the radiation pattern analysis of reflector antennas and planar near field to far field (NF-FF) transformation) is presented and illustrated through a typical example. Employing this technique and a discrete Fourier series (DFS) expansion for the integrand, a method for computing the radiation integrals of reflector antennas and planar NF-FF transformation integrals at arbitrary observation angles with optimum use of computer memory and time is also described.
A new method is developed for determining the farfield pattern of an antenna from probe compensated near-field measurements over the surface of a right circular cylinder enclosing the antenna. The method is derived by first expanding both the field radiated by the antenna and the field radiated by the measurement probe, when it is used as a transmitter, into cylindrical wave expansions. The Lorentz reciprocity theorem is then used to solve for the field radiated by the antenna from the probe output voltage. It is shown rigorously that the antenna pattern can be determined independently of the characteristics of the measurement probe provided that certain calibration data are known. A method for determining these data from the measured far field radiated by the probe is described. It is shown that the necessary numerical integration can be performed with the fast Fourier transform algorithm. Experimental results are presented to validate the theory and to demonstrate its practicality from a measurement and computational viewpoint.
A sample spacing criterion and a data minimization technique for measurements made over the surface of a plane in the near field of an antenna are presented. The sample spacing is shown to depend on the distance from the antenna to the measurement plane, and on the extent to which evanescent waves can be neglected. The near-field data minimization technique utilizes two-dimensional spatial filtering to effect a significant reduction in computational effort required to calculate selected portions of the far-field pattern. Far-field patterns of an X band antenna calculated from near-field measurements are presented and compared with those measured on a standard far-field range. The far-field calculations are repeated for several near-field sample spacings and for various post-filter sample rates.
Spherical-wave expansions are a well-known technique of expressing electromagnetic field data. However, most previous work has been restricted to idealized cases in which the expansion coefficients are obtained analytically. In this paper spherical-wave expansions are used as a numerical technique for expressing arbitrary fields specified by analytical, experimental, or numerical data. Numerical results on the maximum wave order needed to expand fields arising from a source of a given size are given for two practical cases, and it is found that the generally accepted wave order cutoff value corresponds to 99.9 percent or more of the power in the input pattern. Near-field patterns computed from far-field data are compared to measured data for the two cases, demonstrating the excellent numerical accuracy of the technique.
Presented here is a method for computing near- and far-field
patterns of an antenna from its near-field measurements taken over an
arbitrarily shaped geometry. This method utilizes near-field data to
determine an equivalent electric current source over a fictitious
surface which encompasses the antenna. This electric current, once
determined, can be used to ascertain the near and the far field. This
method demonstrates the concept of analytic continuity, i.e., once the
value of the electric field is known for one region in space, from a
theoretical perspective, its value for any other region can be
extrapolated. It is shown that the equivalent electric current produces
the correct fields in the regions in front of the antenna regardless of
the geometry over which the near-field measurements are made. In this
approach, the measured data need not satisfy the Nyquist sampling
criteria. An electric field integral equation is developed to relate the
near field to the equivalent electric current. A moment method procedure
is employed to solve the integral equation by transforming it into a
matrix equation. A least-squares solution via singular value
decomposition is used to solve the matrix equation. Computations with
both synthetic and experimental data, where the near field of several
antenna configurations are measured over various geometrical surfaces,
illustrate the accuracy of this method
The complex bi-conjugate gradient iterative method is applied to
an isoparametric boundary integral equation formulation for
frequency-domain electromagnetic scattering problems. It is demonstrated
to work well on large and geometrically complex examples, including a 20
wavelength slender dipole, the NASA almond, and a resonant cavity. On
such problems, with asymmetric curvilinear irregular meshes and
nontrivial geometries, the number of iterations required seems to
increase rather more than linearly with body size, indicating an overall
~sixth power cost scaling. This scaling is essentially as for direct
methods, but with costs still a small fraction of the direct approach. A
method is proposed for the selection of a termination condition designed
to avoid seeking the approximate answer too precisely; it typically
permits a further halving of costs
An alternative method is presented for computing far-field antenna
patterns from near-field measurements. The method utilizes the
near-field data to determine equivalent magnetic current sources over a
fictitious planar surface that encompasses the antenna, and these
currents are used to ascertain the far fields. Under certain
approximations, the currents should produce the correct far fields in
all regions in front of the antenna regardless of the geometry over
which the near-field measurements are made. An electric field integral
equation (EFIE) is developed to relate the near fields to the equivalent
magnetic currents. The method of moments is used to transform the
integral equation into a matrix one. The matrix equation is solved with
the conjugate gradient method, and in the case of a rectangular matrix,
a least-squares solution for the currents is found without explicitly
computing the normal form of the equation. Near-field to far-field
transformation for planar scanning may be efficiently performed under
certain conditions. Numerical results are presented for several antenna
configurations
The possibility of determining the far field of radiating systems
by measuring only the near-field amplitude is investigated. The main
difficulties of the problem are examined in some detail and a new
near-field/far-field transformation technique is developed, based on the
measurement of the near-field amplitude over two surfaces surrounding
the antenna under test. The accuracy of the far-field reconstruction
results are related both to the distance between such surfaces and to
some a priori information concerning the near-field phase and/or the
radiating system. The information on the radiating system allows
relaxation of the need for any information on the near-field phase
provided that the distance between the measurement surfaces is high
enough. Conversely, the knowledge of a more or less corrupted near-field
phase allows reduction of such distances without affecting the accuracy
of the far-field reconstruction. Numerical examples validating the
effectiveness of the developed algorithm are provided for the planar
scanning case
A spherical-scan near-field antenna range is described. The
procedure for real-time data processing is outlined. Relations for the
number of data points, largest aspect angle measured, and data
acquisition and processing times as a function of the antenna
diameter-to-wavelength ratio and the measurement distance are given.
Experimental results are presented for an antenna enclosed by a minimum
sphere having a diameter of 240 wavelengths. All the equations for the
spherical wave analysis, probe correction, and radial transformation are
provided in appendices in numerically convenient form without the use of
any special functions
Using computer simulation, several fundamental issues in planar
near-field measurement are examined. The results indicate that some of
the prevailing views of practices regarding the evanescent modes, the
sampling and filtering of data, and the selection of the location and
directivity of the probe are incomplete or misleading. In particular,
the merits of using smaller low-directivity probes in conjunction with a
closer probe-to-antenna distance have been found to be unduly overlooked
Directividad en el plano de elevación φ=π/2, el archivo ELECCION.DAT debe tener la siguiente forma: 2 1
- La Para Obtener
Para obtener la Directividad en el plano de elevación φ=π/2, el archivo
ELECCION.DAT debe tener la siguiente forma:
2
1.570796
- A Cardama
- Jofre Roca
Cardama A., Jofre Roca L., Rius J. Blanch S. Antenas. (Libro).-Méjico:
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Un Algoritmo de Transformación de campo cercano a campo lejano aplicado a sistemas radiantes de geometría arbitraria utilizando fuentes de corriente equivalente del tipo magnético en sistema coordenado cilíndrico
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- L Núnez
Martínez F., Arruebarrena R., Núnez L. Un Algoritmo de Transformación de
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