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Showing papers on "Near and far field published in 1992"


Journal ArticleDOI
TL;DR: It is reported that small particles with diameters of 1-27 microm have moved in the evanescent fields produced by a laser beam.
Abstract: We report that small particles with diameters of 1–27 μm have moved in the evanescent fields produced by a laser beam. The evanescent field in the experiment was produced in the near field of the surface of a high-refractive-index sapphire prism illuminated by a 1.06-μm YAG laser beam with an incident angle larger than the critical angle. Both polystyrene latex spheres and glass spheres bounced and ran along the surface of the prism when the laser beam was on. The maximum running speed obtained was approximately 20 μm/s. A micrograph of the running particles is shown with plots of the measured velocity versus the incident angle of the laser beam. Applications of this phenomenon are also discussed.

355 citations


Journal ArticleDOI
Niels Kuster1, Q. Balzano2
TL;DR: In this article, the energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations and all computations are performed and validated applying the three-dimensional multiple multipole software package.
Abstract: The energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations. All computations are performed and validated applying the three-dimensional multiple multipole software package. The numerical model of the plane phantom is additionally checked by accurate as possible experimental measurements. For the plane phantom, the interaction mechanism can be described well by H-field induced surface currents. The spatial peak specific absorption rate can be approximated within 3 dB by a formula given here based on the incident H-field or antenna current and on the conductivity and permittivity of the tissue. These findings can be generalized to heterogeneous tissues and larger biological bodies of arbitrary shape for frequencies above 300 MHz. The specific absorption rate is mainly proportional to the square of the incident H-field, which implies that in the close near field, the spatial peak specific absorption rate is related to the antenna current and not to the input power. >

321 citations


Journal ArticleDOI
TL;DR: In this article, an electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents, and the method of moments is used to transform the integral equation into a matrix one.
Abstract: 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. >

260 citations


Journal ArticleDOI
TL;DR: The position of an atom passing through a standard light wave is localized by making a quadrature phase measurement on the light field, which can be thought of as the creation of a virtual slit for the atom by the field measurement.
Abstract: The position of an atom passing through a standard light wave is localized by making a quadrature phase measurement on the light field. This localization can be thought of as the creation of a virtual slit (or slits) for the atom by the field measurement. Diffraction and interference behavior may be observed in the far field.

177 citations


Journal ArticleDOI
TL;DR: In this article, a generalized tomographic reconstruction procedure is described for determining the complex-valued index-of-refraction distribution of a semitransparent, three-dimensional inhomogeneous object from observations of the far-field intensity patterns generated by the object in a sequence of scattering experiments.
Abstract: A generalized tomographic reconstruction procedure is described for determining the complex-valuedindex-of-refraction distribution of a semitransparent, three-dimensional inhomogeneous object from observations of the far-field intensity patterns generated by the object in a sequence of scattering experiments. The inversion procedure is based on the wave equation governing the scattered optical field and fully accounts for the diffraction and propagation effects associated with the interaction of the incident wave with the object and the subsequent free-space propagation of the scattered wave to the wave zone (far field). The reconstruction of the object’s index-of-refraction distribution is performed digitally directly from the far-field intensity of the scattered wave and does not require direct measurement or retrieval of the phase of the scattered field. An optical scattering experiment is reported in which the cross-sectional profile of the index-of-refraction distribution of an optical fiber is reconstructed from the measured intensity of the diffraction pattern of the fiber by using the described inversion procedure.

94 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array and supported them with numerical calculations, and showed that for certain measures of performance involving these beam characteristics, a localized wave pulse driven array can outperform similar continuous-wave-driven arrays.
Abstract: Analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array are derived and supported with numerical calculations. These bounds extend the meaning of near-field distances or diffraction lengths to the situation where the array driving functions can be broad-bandwidth signals. Particular attention is given to transmitting and receiving array systems which consist of elements that are not large in comparison to the shortest wavelength of significance contained in the signals driving them. Their output signals constitute higher-order beams whose coherence properties are degraded more slowly by diffraction than lower-order beams. It is shown that for certain measures of performance involving these beam characteristics, a localized wave pulse-driven array can outperform similar continuous-wave-driven arrays. An array with independent addressable elements is required to realize these localized wave effects. The enhanced localization effects are intimately coupled to the proper spatial distribution of broad-bandwidth signals driving the array. >

93 citations


21 Sep 1992
TL;DR: In this paper, an antenna array was used to generate a uniform electromagnetic field in a rectangular chamber, which was analyzed and compared with the conventional reverberating chamber, or mode-stirred chamber, leading to some interesting results.
Abstract: The idea of the source-stirred chamber for performing electromagnetic compatibility measurements is introduced. The electromagnetic field inside the conducting rectangular chamber with arbitrary dimensions is obtained using the corresponding dyadic Green's function. The computer simulation shows that an evenly homogeneous isotropic field can be created by controlling the excitation source. It is found that the key to perturbing the field effectively lies in shifting the weighting factor of each mode excited in the chamber. The behaviour is analyzed and compared with that of the conventional reverberating chamber, or mode-stirred chamber, leading to some interesting results. It indicates that, instead of the mode-stirrer, an antenna array may be used to generate a uniform electromagnetic field in a rectangular chamber. >

71 citations


Journal ArticleDOI
TL;DR: In this article, an array of photoconducting antennas which generates electrically controllable millimeter-wave and sub-millimeterwave radiation in free space is described, where the emitted radiation is directional and electrically steerable, and can be scanned through an angle of over 40 degrees.
Abstract: An array of photoconducting antennas which generates electrically controllable millimeter-wave and submillimeter-wave radiation in free space is described. Under quasi-sinusoidal optical illumination, the emitted radiation is directional and electrically steerable, and can be scanned through an angle of over 40 degrees . The center of the scanning range can be adjusted by changing the angle of incidence of the pump beam. The far-field radiation pattern of the array is measured and discussed. Also, some properties of the array under illumination by a short optical pulse are demonstrated. These include electrical control of the frequency content of the signal and mapping of the spatial profile of the applied electric field onto the radiated waveform. The latter property can be used to multiplex information presented in parallel into a train of radiated pulses with a bit spacing of 6 ps. >

70 citations


Journal ArticleDOI
TL;DR: This paper points out the importance ofevanescent waves in near-field optics and makes the connection between resolving power and evanescent fields.
Abstract: The experimental resolution that is obtained with a near-field microscope by optical tunneling detection is far beyond the Rayleigh criterion. We discuss the principal physical characteristics of this superresolution. Three different examples are presented. They show that the resolution increases as the collector width and collector-to-object distance decrease. It is interesting to note that, in the near-field microscope, as in all local probe microscopes, the resolution cannot be defined from the characteristics of the microscope only. In all tunnel devices the detector cannot be separated from the object. The superresolution that can be obtained results from this fact. This paper also points out the importance ofevanescent waves in near-field optics and makes the connection between resolving power and evanescent fields.

66 citations


Patent
21 May 1992
TL;DR: In this article, a method and apparatus for sensing proximity of an object using near-field effects is presented, where the antenna radiates this modulated radio frequency energy to charge the surface of the object.
Abstract: A method and apparatus for sensing proximity of an object using near-field effects Modulated radio frequency energy is fed to an antenna The antenna radiates this modulated radio frequency energy to charge the surface of an object When the position of the object changes, the impedance of the antenna due to near-field effects changes This impedance change is detected to provide an indication of the object's movement The sensing device may be packaged to be inserted into a wall to provide a sensor having a leak-free seal

61 citations


Patent
17 Nov 1992
TL;DR: In this paper, a spatially-dependent phase shift in the electromagnetic field generated by the power transmitter was developed for power coupling independent of the position of the receiver over a surface.
Abstract: A system for power coupling independent of the position of the receiver over a surface. This is achieved by developing a spatially-dependent phase shift in the electromagnetic field generated by the power transmitter. The power inputs to the power receiver are then driven 180 degrees out of phase at any coordinate in the plane over the surface. An array of elements is placed in a plane below a surface and driven with a series of alternating current power sources. Consecutive adjacent elements across the area of the plane are driven with uniformly increasing phase shift. An integral multiple of adjacent consecutive elements results in a 180 degree phase shift. Pairs of field receiving elements in a power receiver are dimensioned to receive fields that are separated by 180 degrees of phase. Utilizing the technique of the invention, power coupling independent of the position or rotational orientation of the power receiver can be obtained.

Journal ArticleDOI
TL;DR: In this paper, a self-consistent method was developed to analyze the influence of incident light beam polarization on an image shape recently recorded from scanning tunneling optical devices, and the electromagnetic coupling between the object and a nanometer-size detector was described from a dynamic matrix including all dipolar correlations inside the system.
Abstract: A whole self-consistent method is developed in order to analyze the influence of incident light beam polarization on an image shape recently recorded from scanning tunneling optical devices. The electromagnetic coupling between the object and a nanometer-size detector is described from a dynamic matrix, including all dipolar correlations inside the system. This matrix, expressed in terms of field propagators, permits us to analyze the physical mechanisms responsible for the conversion of evanescent waves into homogeneous propagating modes inside the detector. The numerical results are compared with those obtained for layered metallic or dielectric nanoparticles deposited upon a glass substrate. The shape and the contrast of the images are both sensitive to the field polarization and to the external frequency in the case of metallic objects. Moreover, as was observed in experimental studies, the p-polarized mode seems to give better contrast in the images.

Journal ArticleDOI
TL;DR: The instrumentation and measurement techniques used for this study described and the results were found to be well below accepted exposure limits even when extrapolated to simultaneous and continuous operation of the maximal number of transmitters that would be expected to be installed at a cell-site.
Abstract: Because of a heightened public awareness of issues pertaining to the use of electromagnetic energy, concurrent with a rapid growth of the cellular telephone industry, a study was initiated to characterize the electromagnetic environment associated with typical cellsite antennas. In particular, the radio-frequency electromagnetic (RF) fields in the vicinity of several antenna towers, ranging in height from 46–82 m, were characterized by measurement. In all cases, the antennas were omnidirectional co-linear arrays. The maximal power densities considered representative of public exposure were found to be less than 100 μW/m2 (10 nW/cm2) per radio channel. Comparison of measured values with the corresponding values that were calculated from the free-space transmission formula indicated that the analytical technique is conservative (i.e., overestimates field levels). The measured and corresponding analytical values were found to be well below accepted exposure limits even when extrapolated to simultaneous and continuous operation of the maximal number of transmitters that would be expected to be installed at a cell-site. Additional measurements were made in the near field of the same antenna type in a roofmounted configuration. At a distance of 0.7 m from the antenna, the maximal power density in the main beam was found to be less than 30 W/m2 (3 mW/cm2) when normalized to sixteen radio channels (the maximal number used on a single antenna) and less than 30 mW/m2 (3μW/m2) at 70 m. In all cases, the effective radiated power (ERP) by each radio channel was 100 W referenced to a half-wave dipole. This paper describes the instrumentation and measurement techniques used for this study and provides a summary of the results. 1992 Wiley-Liss, Inc.

Journal ArticleDOI
TL;DR: Theoretical analysis and some experiments are performed on nonlinearly generated harmonic components in bounded sound beams emitted from a rectangular aperture source as mentioned in this paper, which takes account of nonlinearity, dissipation, and diffraction effects in the beams, numerically solved by means of the alternating direction implicit difference method.
Abstract: Theoretical analysis and some experiments are performed on nonlinearly generated harmonic components in bounded sound beams emitted from a rectangular aperture source The Khokhlov–Zabolotskaya–Kuznetsov equation, which takes account of nonlinearity, dissipation, and diffraction effects in the beams, is numerically solved by means of the alternating direction implicit difference method Using a planar source of size 24×44 cm, axial sound pressures and beam patterns of the first three harmonics are measured in air for initially sinusoidal ultrasounds of 25‐ and 30‐kHz frequency, and are compared with the theory They are in relatively good agreement Deformation of the source face from circular to rectangular shape results in the unclear appearance of pressure peaks and dips with propagation Within the framework of these studies, the harmonic pressure levels in the far field are almost the same as from a circular aperture source with equal face area and equal initial pressure, independent of the source le

Journal ArticleDOI
TL;DR: An algorithm valid for an accurate calculation of the near-field in the scanning plane of ultrasonic phased arrays is presented, and some numerical examples are presented, in which the advantages of using the array impulse response in the field analysis are shown.
Abstract: An algorithm valid for an accurate calculation of the near-field in the scanning plane of ultrasonic phased arrays is presented. Using the classical time-domain impulse response approach, a simple analytical expression for the impulse response at points lying in the central plane of a narrow rectangular aperture is decided. An expression for the array impulse response is then obtained by superposition. The proposed solution is useful for an efficient computation of transient and continuous wave (CW) pressure fields without requiring any far-field or paraxial approximations. Moreover, the convolution-impulse response approach applied to phased arrays constitutes an important tool for the analysis of array fields. Some numerical examples are presented, in which the advantages of using the array impulse response in the field analysis are shown. Several aspects of array fields not currently described in literature are included in the examples. >

Patent
31 Jul 1992
TL;DR: In this article, a large current radiator with a small antenna length s by using a design wherein the antenna current is n times larger than the drive current is disclosed. And, since n can be 10,000 or more, the antenna currents can be in the kilo Ampere range and beyond with a moderate drive current.
Abstract: A radiator useful for radiating pulses with a duration of about 10 ms is disclosed. Such pulses occupy the frequency band from zero to a few hundred Hertz. For a given time variation of an electromagnetic signal, the energy radiated in the far field is proportional to (Is) 2 , where I is the current amplitude in the antenna and s is the length of the radiator. Typical antenna designs cannot be used at very low frequencies with large relative bandwidths. However, the large current radiator disclosed, herein, is small, has antenna currents in the order of 10 8 A, and requires a drive voltage of about 1 volt and drive current of 10 4 A. This large current radiator is designed with a small antenna length s by using a design wherein the antenna current is n times larger than the drive current. This is accomplished by winding electrically conductive means n times around a shield so that the n forward loop wires are all on one side of the shield, and cover a surface area sxW. The n return loop wires are on the opposite side of the shield and are confined so that they cover a surface area that is very small compared to the area of the forward loop. Furthermore, the shield is fabricated to reflect the electromagnetic energy produced by the forward loop and absorb the electromagnetic energy produced by the return loop. Hence, the antenna is highly efficient. And, since n can be 10,000 or more, the antenna current can be in the kilo Ampere range and beyond with a moderate drive current.

01 Jan 1992
TL;DR: In this article, an experimental technique that makes use of the intensity of the interference pattern formed by light that propagates directly from the singlemode fiber tip and light that is reflected by the surface under anoblique angle of incidence is developed to control the tip-surface distance in near-field optical microscopy.
Abstract: An experimental technique that makes use of the intensity of the interference pattern formed by light that propagates directly from the single-mode fiber tip and light that is reflected by the surface under anoblique angle of incidence is developed to control the tip-surface distance in near-field opticalmicroscopy. It is shown that by using another fiber as a detector with a polished edge placed at the surface near the fiber tip one can determine the tip-surface separation with an accuracy better than 15 nm at distances less than 1 µm. The technique proposed is used to investigate the influence of the shape of the tip in near-field measurements.

Journal ArticleDOI
01 Aug 1992
TL;DR: In this article, a new method for recovering the complex near and far field from amplitude distributions collected over two near zone surfaces is proposed by exploiting the mathematical properties of the radiated fields and choosing an appropriate functional of the data, the solution is found through the minimisation of the introduced functional.
Abstract: A new method for recovering the complex near and far field from amplitude distributions collected over two near zone surfaces is proposed. By exploiting the mathematical properties of the radiated fields and choosing an appropriate functional of the data, the solution is found through the minimisation of the introduced functional. All details of the resulting iterative procedure are worked out for the cylindrical scanning in the three dimensional vector case where the implementation turns out to be effective thanks to a proper use of the FFT algorithm. It is shown that this new approach allows the solution to be obtained starting from a completely arbitrary point, so avoiding the local minima problem.

Journal ArticleDOI
TL;DR: In this article, the radiation of an elementary dipole placed inside an infinite triaxial anisotropic medium is analyzed using a Fourier analysis. But the authors focus on the near and far field expressions obtained by pursuing integration of the Fourier integrals.
Abstract: The radiation of an elementary dipole placed inside an infinite triaxial anisotropic medium is analyzed. A Fourier analysis is employed to compute the field which is represented by using a dyadic formulation. The near and far field expressions are obtained by pursuing integration of the Fourier integrals. Conventional spherical scalar wave functions are employed to represent the dyadic Green's functien. Singularity source terms of the Green's function dominant in the near field region, are treated independently. Two separate spherical waves compose the far field, where also a non-zero radial term appears.

Patent
24 Jun 1992
TL;DR: In this paper, a planar near-field antenna measurement and diagnostic system is described which collects data on a bi-polar grid using rotary positioners and a mechanical arm.
Abstract: A planar near-field antenna measurement and diagnostic system is described which collects data on a bi-polar grid. The planar scanning is accomplished using rotary positioners and a mechanical arm. The test antenna is mounted to a rotary positioner such that it can spin about its axis. The arm is mounted to another rotary positioner such that it can rotate about a second axis. A field probe, attached to the end of the arm, scribes an are which passes through the antenna rotation axis. By rotating the two positioners, the near-field of the antenna can be measured on a bi-polar sampling grid comprising concentric circles and radial arcs. The mechanical simplicity afforded by rotational motion rather than the linear motion of most planar near-field scanners provides for an elegant and cost-effective design.

21 Sep 1992
TL;DR: In this article, a generalised solution to the electromagnetic field excited by a current source inside a moving wall mode-stirred rectangular chamber is presented by using the dyadic Green's function for the chamber.
Abstract: A generalised solution to the electromagnetic field excited by a current source inside a moving wall mode-stirred rectangular chamber is presented by using the dyadic Green's function for the chamber. A detailed discussion of the field inside the chamber is given. The polarization of the field is also illustrated. The solution shows that a uniformly random electromagnetic field, both in amplitude and polarization, can be obtained by a suitable choice for the excitation and the stirrer. This is in good agreement with the previous experimental results.

Journal ArticleDOI
TL;DR: The wave equation of electromagnetic field coupling with TO phonons in second-order nonlinear dielectrics is derived and theoretical calculation shows that the propagation of electromagnetic pulses without distortion in the dispersive medium is possible due to the dependence of the index of refraction on the electromagnetic field.
Abstract: We have derived the wave equation of electromagnetic field coupling with TO phonons in second-order nonlinear dielectrics. If the loss of the medium can be ignored, theoretical calculation shows that the propagation of electromagnetic pulses without distortion in the dispersive medium is possible due to the dependence of the index of refraction on the electromagnetic field. This electromagnetic field is governed by a Boussinesq equation that has soliton solutions. If the loss of the medium is sufficiently strong that the damping distance is much smaller than the signal width, we find electromagnetic shock-wave solutions. Possible experiments in ${\mathrm{LiTaO}}_{3}$ are discussed.

Journal ArticleDOI
TL;DR: Electromagnetic optical interactions between a small metal sphere and a metallic surface are studied by using a self-consistent approach in the presence of an external field to determine the intensity scattered by the metal particle for different polarizations of the incident field.
Abstract: Electromagnetic optical interactions between a small metal sphere and a metallic surface are studied by using a self-consistent approach in the presence of an external field. The intensity scattered by the metal particle is given for different polarizations of the incident field. This quantity, determined from a local treatment of the response function of the two interacting systems, exhibits a spatial dependence with respect to the approach distance close to that obtained from recent experimental studies. Moreover, at large separation, retardation effects included from a dipolar propagator give rise to pseudoperiodic oscillations such as the ones observed in reflection near-field optical microscopy. In the near-field range, plasmon modes of the whole system probe surface introduce narrow resonances in the scattered intensity versus the probe–sample separation.

Journal ArticleDOI
TL;DR: In this paper, the problem of electromagnetic scattering from a conducting or dielectric rough surface with arbitrary shape is studied, and an exact solution, using a differential method, is provided for a plane wave with one-dimensional irregularity of the interface.
Abstract: The problem of electromagnetic scattering from a conducting or dielectric rough surface with arbitrary shape is studied. An exact solution, using a differential method, is provided for a plane wave with one-dimensional irregularity of the interface. The problem is reduced to the resolution of a linear system of partial differential equations with constant coefficients, and to the computation of eigenvalues and eigenvectors of a truncated infinite matrix. Numerical application is made to show the angular distribution of energy density in the case of an arbitrary profile of the scattering surface and its evolution when the nonperiodic profile tends to become periodic. The near field is computed on the interface and its enhancement in the illuminated region is observed. It increases with the height of the irregularity and with the frequency. >

Journal ArticleDOI
TL;DR: In this paper, a semi-analytical procedure was developed to treat scattering of horizontally polarized electromagnetic waves from underground cylindrical inhomogeneities, where the air-ground interface was assumed to have a sinusoidal profile.
Abstract: A semi-analytical procedure has been developed to treat scattering of horizontally polarized electromagnetic waves from underground cylindrical inhomogeneities. The air-ground interface is assumed to have a sinusoidal profile. The proposed procedure uses Green's functions theory together with the principle of extended boundary conditions. The unknown electric field inside the scatterer is determined by solving an appropriate integral equation over the cross section of the scatterer. Then the far field in the air is evaluated by employing the steepest descent approximation and the normalized scattering amplitude is plotted for several cases.

Proceedings ArticleDOI
18 Jun 1992
TL;DR: In this paper, the authors presented an imaging near-field spherical wave inverse synthetic aperture radar (SWISAR) algorithm based on a focusing operator of the scattered fields on the target surface.
Abstract: The authors present an imaging near-field spherical wave inverse synthetic aperture radar (SWISAR) algorithm based on a focusing operator of the scattered fields on the target surface. A spherical wave can be easily generated in an anechoic chamber using electrically small and low-cost horn antennas; no reflectors are used, avoiding surface tolerance problems, and diffraction can be minimized with an appropriate horn design. An additional advantage of this algorithm is its ability to account for bistatic measurement geometries and lateral tapers in the spherical wave illumination. A 2-D formulation has been used which is strictly valid for bodies which satisfy far-field conditions in the height dimension, as easily occurs with aircraft. The reconstruction of numerically simulated five point-like objects placed on a radial line for a frequency range of 18 to 26 GHz and an angular scan of 360 degrees is shown. >

Journal ArticleDOI
TL;DR: In this article, the authors proposed a near field to far field projection technique based on the identification from the measured data of an equivalent monopolar distribution of acoustic sources on a surface completely surrounding the radiator.
Abstract: The near‐field to far‐field projection procedure here introduced has the following novel features. (1) The measured near‐field samples do not need to belong to a separable coordinate surface. (2) The number of samples is, in principle, as small as the theoretical number of degrees of freedom of the far field, related to the dimensions of the source in wavelengths. (3) The samples do not need to belong to a regular grid. (4) If the projection is sought only within a limited angular sector, a further reduction of the number of measurement samples is possible. The technique is based on the identification from the measured data of an equivalent monopolar distribution of acoustic sources on a surface completely surrounding the radiator. The far field of these sources, straightforwardly computed, constitutes the estimate of the far field of the radiator. The identification is based on the pseudo inversion of the matrix representing the mapping of the equivalent sources into near‐field samples, which is obtained by resorting to the singular value decomposition of the matrix. Representative results of the extensive numerical simulations are here included.

Journal ArticleDOI
TL;DR: In this paper, the FD-TD method is applied to model transverse electromagnetic (TEM) transmission cells in three dimensions and the perturbation of the TEM mode and the standard field distribution due to inhomogeneous materials placed inside the cell cavity is evaluated.
Abstract: The finite-difference-time-domain (FD-TD) method is applied to model transverse electromagnetic (TEM) transmission cells in three dimensions. The perturbation of the TEM mode and the standard field distribution in the TEM cell, due to inhomogeneous materials placed inside the cell cavity, is evaluated. Particularly, the dependence of the disturbance of the TEM mode on the dimensions of the material and its position in the TEM cell is studied. The absorption of the electromagnetic fields in the lossy materials, placed in the cell, is also calculated. >

Proceedings ArticleDOI
C.E. Baum1
18 Jun 1992
TL;DR: In this paper, the authors evaluated the aperture efficiencies of a conical TEM (transverse electromagnetic) feed for a paraboloidal reflector (or a lens if desired) and showed that the feed arms are terminated (primarily resistive) at the reflector to minimize multiple reflections and to improve the limited low-frequency performance by balancing the electric and magnetic dipole moments.
Abstract: The IRA (impulse radiating antenna), consists of a special kind of conical TEM (transverse electromagnetic) feed launching a step-rising wave on an aperture after conversion of the spherical wave to a plane wave via a paraboloidal reflector (or a lens if desired). The radiated field has an important part which is a narrow impulse, although there is a comparatively low-amplitude, slow undershoot to give a net zero time integral in the far field. The feed arms are terminated (primarily resistive) at the reflector to minimize multiple reflections and to improve the limited low-frequency performance by balancing the electric and magnetic dipole moments for forward (from the reflector) radiation. There are various possible configurations of the TEM conical feed and feeding coaxial cables (and possible baluns as well) to allow for a variety of characteristic impedances. Aperture efficiencies for IRAs are evaluated. >

Journal ArticleDOI
TL;DR: In this paper, a probe-corrected vector transmission formula and a rigorous sampling-reconstruction theorem for near-field antenna measurements in plane-polar coordinates are derived from three fundamental theorems of antenna theory.
Abstract: A probe-corrected vector transmission formula and a rigorous sampling-reconstruction theorem for near-field antenna measurements in plane-polar coordinates are derived from three fundamental theorems of antenna theory: the mutual coupling function between two antennas satisfies the homogeneous wave equation; a receiving antenna can be represented as a differentiator of the incident field; and the mutual coupling function is virtually bandlimited. The rigorous sampling equations are applied to compute the far fields of a circular-aperture antenna sampled in the near field at half-wavelength radial spacing. >