Showing papers in "IEEE Transactions on Antennas and Propagation in 1970"
TL;DR: In this article, the boundary value problem of an infinite array of thin plates arranged in a doubly periodic grid along any two coordinates is formulated in a general form for an arbitrarily polarized plane wave incident from any oblique angle.
Abstract: The boundary value problem of an infinite array of thin plates arranged in a doubly periodic grid along any two coordinates is formulated in a general form for an arbitrarily polarized plane wave incident from any oblique angle. The induced current on the plate, the near-field distribution, and the distant reflected waves can be obtained to a very close accuracy. Both magnitudes and phases of the reflection coefficients for some specific examples are determined explicitly. For the case of a wave incident normally on a rectangular lattice array of narrow rectangular plates, the calculated values are in excellent agreement with the measurements in a previously published paper.
210Â citations
TL;DR: In this article, the propagation of waves in media which are spatially homogeneous but whose properties vary with time abruptly or continuously is examined, and a comparison is made between the asymptotic results and the exact solutions noted above.
Abstract: This paper examines the propagation of waves in media which are spatially homogeneous but whose properties vary with time abruptly or continuously. Emphasis is placed on the excitation problem and on source-dependent phenomena which are not evident when attention is given only to the source-free case. After a presentation and interpretation of various exact closed-form solutions for simple nondispersive and dispersive media undergoing sudden or gradual temporal changes, attention is given to integral representations required under more general conditions. In the ensuing far-zone asymptotic analysis, dispersion surfaces and space-time rays are used extensively for identification of wave packets and other wave constituents descriptive of the field, and a comparison is made between the asymptotic results and the exact solutions noted above. Asymptotic field solutions are then derived by a direct ray procedure, without intervention of integral representations. The examples considered exhibit a variety of phenomena, among which the most interesting is the focusing of reflected waves when a dispersive medium undergoes a sudden change.
140Â citations
TL;DR: In this paper, a novel and rigorou formulation for mutual impedance among a class of idealized but realizable antennas is presented, where all the electromagnetic properties of which are rigorously expressed explicitly in terms of their radiation patterns alone.
Abstract: A novel and rigorou formulation for mutual impedance among a class of idealized but realizable antennas is presented. Unlike past treatments of mutual coupling, which have proceeded from structurally specified antennas, the present treatment deals with a class of antennas, all the electromagnetic properties of which are rigorously expressed explicitly in terms of their radiation patterns alone. Employing a network formulation based on a scattering representation of electromagnetic fields in terms of spherical (or cylindrical) modes, the mutual impedances between such antennas are computed exactly. Several alternate representations for the mutual impedance are derived, one of which is an integral representation involving the power pattern function for both real and complex angles. In special cases, these exact results agree with published results obtained by applying well-known approximate techniques to structurally specified antennas. An important and illuminating example is provided by an infinite planar array of antennas radiating into a half-space for which the present formulation yields the well-known grating-lobe series representation of the active impedance without an explicit reference to structural properties of the radiating elements.
129Â citations
IBM1
TL;DR: In this paper, the phase center for an arbitrary plane is calculated from the E- and H -plane phase centers, and the dependence of the phase centers on horn dimensions is shown. But this is based on a vector approach, by deriving the phase centre from the expressions for the far field.
Abstract: The calculation of phase centers for rectangular and diagonal horns is presented. The calculation is based on a vector approach, by deriving the phase center from the expressions for the far field. Different expressions are derived for the phase center of the E and H planes. The phase center for an arbitrary plane is calculated from the E- and H -plane phase centers. Graphs are presented showing the dependence of the phase centers on horn dimensions.
106Â citations
TL;DR: In this paper, a method for determining the fields scattered by arbitrarily shaped cylindrical conducting structures with a transient incident wave is described, where the transient scattering problem is reduced to the solution of a time domain integral equation which in turn is solved directly in the time domain by means of a digital computer.
Abstract: A method for determining the fields scattered by arbitrarily shaped cylindrical conducting structures with a transient incident wave is described. The transient scattering problem is reduced to the solution of a time domain integral equation which in turn is solved directly in the time domain by means of a digital computer. The approximate electromagnetic impulse response for a number of cylindrical scatterers is calculated using this method.
92Â citations
TL;DR: A procedure is presented for predicting by computer the radiation pattern of an antenna in the presence of a radome, and good agreement between theory and experiment is noted.
Abstract: A procedure is presented for predicting by computer the radiation pattern of an antenna in the presence of a radome. The case of a horn antenna radiating through an actual aircraft radome is treated in detail, and a comparison is made between computed and measured antenna patterns. Good agreement between theory and experiment is noted.
84Â citations
TL;DR: In this paper, the authors used the knowledge of the incident field and the scattered far field at one frequency to determine the size, shape, and location of a perfectly conducting scatterer.
Abstract: It is demonstrated that the knowledge of the incident field and the scattered far fields at one frequency may be employed to determine the size, shape, and location of a perfectly conducting scatterer. The reconstruction of the scattering body is accomplished via an analytic continuation procedure that generates the fields in the neighborhood of the scatter from the specified far-field distribution. The geometry of the body is then determined by locating a closed surface for which the total tangential electric field, i.e., the sum of the tangential components of the incident and scattered field, is zero. Whereas exact knowledge of the entire far field is sufficient to determine the scatterer, a technique is also given for size and shape determination when only part of the far field is available. Numerical examples of several different geometries are given for ranges of ka (a the largest dimension of the body) from 0.2 to 10. Geometries considered were elliptic and circular cylinders, conducting strips, and two cylinders. Plots of the fields reconstructed from the far-field data are compared to the known solutions, and the accuracy of the procedure is demonstrated. The effects of noise in the far-field pattern is also considered, and it is shown that even with noise levels of -20 dB the scattering geometry can be recovered.
72Â citations
TL;DR: In this article, the induced EMF formulation was employed to develop a closed-form expression for the mutual impedance between coplanar-skew dipoles, and numerical results were presented in graphical form.
Abstract: The induced EMF formulation is employed to develop a closed-form expression for the mutual impedance between coplanar-skew dipoles, Numerical results are presented in graphical form.
72Â citations
TL;DR: In this article, a modified Babinet's principle is formulated, and this is used to find the diffraction of sound by an acoustically soft circular disk, and the spheroidal wave functions are described and applied to diffraction theory.
Abstract: The three-dimensional diffraction of a scalar plane wave through a circular aperture in an infinite plane screen is analyzed and numerically computed for the case of normal incidence. A modified Babinet's principle is formulated, and this is used to find the diffraction of sound by an acoustically soft circular disk. The spheroidal wave functions are described and applied to the diffraction theory. Numerical values of the rigorous diffraction functions are computed, and these are compared to the approximation obtained by the Huygen-Kirchhoff formulation.
72Â citations
TL;DR: In this article, the feasibility and practicality of improved performance from a stabilized antenna on a synchronous satellite by shaping the beam for optimum earth coverage has been shown and a relatively simple low-loss antenna that gives a good approximation to the ideal pattern is described.
Abstract: The feasibility and practicality of achieving improved performance from a stabilized antenna on a synchronous satellite by shaping the beam for optimum earth coverage is shown. Due to the difference in range and atmospheric attenuation from a synchronous satellite to various points on the earth, a conventional beam with maximum gain toward the center of the earth is inefficient because it has the highest gain where the least gain is required. Since the paths tangential to the earth are longest and since they traverse through more atmosphere, the antenna gain should be highest in this region and decrease to a minimum for the path normal to the earth (see Fig. 1). The flat portions at the edge of the "ideal" pattern allows for stabilization errors of the satellite. The ideal pattern has been calculated to give equal effective signal (including noise due to atmospheric attenuation and assumed preamplifier noise figures of the ground terminal and satellite) over the entire portion of the earth covered by the antenna beam. The ideal pattern is rotationally symmetrical and has the capability of dual orthogonal polarization. A relatively simple low-loss antenna that gives a good approximation to the ideal pattern is described. The antenna is a nine-horn array consisting of a large central horn surrounded by a ring of eight smaller horns. The central horn is multimoded to provide rotational symmetry and polarization purity. An optimum power division and relative phasing between the central and outer horns is made to give a pattern that closely approximates the ideal. Both theoretical and measured data are presented. Measured results confirm the beam shaping, rotational symmetry, polarization purity improved gain, and broad bandwidth expected from the array. A gain improvement of more than 2 dB over a well-designed conventional horn antenna has been demonstrated.
62Â citations
TL;DR: In this article, the determinantal equation was obtained by assuming that the strips are narrow as compared to all other linear dimensions, and the amplitudes of the space harmonics were computed and discussed in connection with the characteristic phenomena such as radiation and coupling.
Abstract: The electromagnetic waves guided by a periodically strip-loaded dielectric slab were investigated. The determinantal equation was obtained by assuming that the strips are narrow as compared to all other linear dimensions. Numerical results involving different combinations of the linear and dielectric parameters are presented in terms of k-\beta diagrams. The amplitudes of the space harmonics were computed and are discussed in connection with the characteristic phenomena such as radiation and coupling. In particular, the relations between the attenuation of the guided waves and the space-harmonic amplitudes are pointed out. As an interesting phenomenon, real solutions have been found to occur in the complex-wave region and this new result has been explained in the light of the space-harmonic amplitudes. The numerical results in the backward-radiation region have been verified experimentally by two different methods: by measuring the phase and amplitude variation in the near field and by calculation from radiation patterns. In both cases, good agreement with the theoretical results has been obtained.
Journal Article•
[...]
TL;DR: In this article, the authors proposed the possibility of designing an antenna having any mean surface, any feeder, and any given radiation pattern by means of holographic technique, and showed that this difficulty can be overcome simply by suitably varying the thickness of the hologram.
Abstract: The extension of holography to the microwave field, for the solution of problems such as antenna synthesis and construction of visible images of microwave illuminated objects, seems to be promising. In preliminary tests, the possibility of designing an antenna having any mean surface, any feeder, and any given radiation pattern by means of holographic technique, is shown. One of the practical problems which is encountered in microwave holography is the construction of the hologram, which requires the antenna to be synthesized. For this purpose, a series of holograms have been constructed and tested based on different approximations of the interference pattern. Another problem encountered is the presence of unwanted orders. Some preliminary tests on phase holograms show that this difficulty can be overcome simply by suitably varying the thickness of the hologram.
TL;DR: In this paper, the existence of multimode propagation in log-periodic dipole arrays was investigated qualitatively in terms of coupling of symmetric and antisymmetric modes by the excitation from an unbalanced line.
Abstract: Standing-wave measurements on a periodic traveling-wave array of dipoles driven with glide-symmetric excitation from a coaxial transmission line show the existence of multimode propagation in certain frequency bands. This phenomenon is explianed qualitatively in terms of coupling of symmetric and antisymmetric modes of the dipole array by the excitation from an unbalanced line. It has not been found when the dipoles are driven from a balanced two-conductor line. The avoidance of such multimode phenomena is crucial to the self-balancing property of successful log-periodic dipole arrays.
TL;DR: In this article, it is shown that a radially symmetric lens can be constructed from natural dielectrics if desired, and a design technique for the optimal antenna is presented.
Abstract: For scanning over wide angles at millimeter wavelengths, an antenna incorporating a radially symmetric lens is an attractive solution if the lens can be realized in a practical form. It is shown that suitable lenses can be constructed very simply, from natural dielectrics if desired, and a design technique for the optimal antenna is presented. Some results are given of analytical and experimental studies of a number of actual antennas operating at wavelengths near 4 mm. These confirm that practical solutions are available. Homogeneous lenses may be used up to antenna gains of about 35 dB, and a lens consisting of a single shell and a core is sufficient for most other practical requirements.
TL;DR: In this paper, the covariance and spectra for amplitude and phase fluctuations for a microwave signal propagated over a line-of-sight path through a turbulent medium are calculated.
Abstract: In this paper the covariance and spectra for amplitude and phase fluctuations for a microwave signal propagated over a line-of-sight path through a turbulent medium are calculated. It is shown that the results derived under the assumption that the wavelength is much smaller than the inner scale of turbulence l_{0} are also valid when the wavelength is equal to or greater than l_{0} .
TL;DR: In this paper, the behavior of log-periodic dipole (LPD) antennas, which are compressed along the transmission-line axis, was studied both experimentally and theoretically, and it was found that compressed LPD antennas are efficient, of low gain, and frequency independent.
Abstract: The behavior of log-periodic dipole (LPD) antennas, which are compressed along the transmission-line axis, is studied both experimentally and theoretically. Compressed LPD antennas are found to be efficient, of low gain, and frequency independent. With compression, the radiation pattern approaches dipole-like behavior and the bandwidth increases slightly. It is also found that LPD antennas exhibit anomalous frequency-dependent behavior in narrow bands of frequencies ( \approx 1/8 of a log period in width) when a reactive termination is used and when the scaling factor \tau is below about 0.92-0.93.
TL;DR: In this paper, a phased array antenna element which provides good circular polarization over a broad sector of coverage in an array environment has been designed and evaluated, where the concept is the superposition of complementary antennas, the dipole, and the slot, to achieve equal E - and H -plane patterns in the array environment.
Abstract: A phased array antenna element which provides good circular polarization over a broad sector of coverage in an array environment has been designed and evaluated. The concept is the superposition of complementary antennas, the dipole, and the slot, to achieve equal E - and H -plane patterns in the array environment. This element, when evaluated in a large test array, demonstrated an ellipticity of less than \pm2.0 dB over a coverage of \pm60 degrees. By proper control of the excitation of the two isolated antennas any desired polarization can be achieved.
TL;DR: In this article, a new variational principle that applies to a wide class of electromagnetic problems is presented, which has the distinctive characteristic of always producing linear algebraic equations when the Rayleigh-Ritz procedure is applied using a trial field composed of a linear combination of variational parameters.
Abstract: A new variational principle that applies to a wide class of electromagnetic problems is presented. This principle has the distinctive characteristic of always producing linear algebraic equations when the Rayleigh-Ritz procedure is applied using a trial field composed of a linear combination of variational parameters. The new technique is applied to a general class of antenna problems, and is specialized to the case of a dielectrically coated slot antenna. Experimentally observed admittance values at X band are presented and compared with theoretical predictions.
TL;DR: In this article, an array of infinitely long longitudinal slots equispaced on a conducting cylinder is analyzed in detail, and expressions for the eigenvalues of these matrices, and for the radiation patterns due to the array eigenexcitations, are found in the form of infinite series rapidly convergent (even for cylinders of large radius).
Abstract: The analysis of multiport antennas may be approached by resorting to the powerful concept of eigenexcitations of the structure. They may be defined as the eigenvectors of the admittance matrix, i.e., those sets of voltages and currents at the antenna terminals which are related simply by a proportionality factor (eigenvalue of the admittance matrix). Similarly, the eigenexcitations may be alternatively defined as the eigenvectors of the scattering matrix. The analysis for this special kind of excitation is sometimes relatively easy. The general case may then be treated by utilizing superposition principle. An array of infinitely long longitudinal slots equispaced on a conducting cylinder is analyzed in detail. The eigenvectors of the admittance and scattering matrices are easily found because of the symmetry of the structure. Expressions for the eigenvalues of these matrices, and for the radiation patterns due to the array eigenexcitations, are found in the form of infinite series rapidly convergent (even for cylinders of large radius). By using linearity an expression for the radiation pattern of the single excited element in the array environment (the main result of this paper) is then established. Expressions are also given for the coupling (or scattering) coefficients. A number of numerical examples with different cylinder radii are discussed in detail.
TL;DR: In this article, the authors present matrix equations for computing the scattered wave of a homogeneous gyrotropic cylinder, where an incident wave with arbitrary polarization is assumed to illuminate the cylinder, which is magnetized along its axis.
Abstract: Matrix equations are given for computing the scattered wave of a homogeneous gyrotropic cylinder. An incident wave with arbitrary polarization is assumed to normally illuminate the cylinder, which is magnetized along its axis. The reciprocity theorem is first applied to the interior of the cylinder. According to the boundary condition, one can replace the tangential components of the total wave on the inside surface by that of the sum of the incident and the scattered waves on the outside surface; the scattered wave is expanded in terms of a series of Hankel functions. Making use of the idea of Waterman's extended integral equation, one obtains the matrix equations to directly determine the expansion coefficients of the scattered wave. The matrix equations have been solved numerically on the NEAC 2200 and the HITAC 5020E for a circular ferrite (or dielectric) cylinder and an elliptic ferrite cylinder. The former solutions are shown to converge to the exact solutions, and the latter scattering patterns of interest are shown in graphical form for an E incident wave. The reciprocity theorem for scattered waves is also examined.
TL;DR: The method of combining wedge diffraction solutions for the analysis of an axial TEM-mode slot is extended here for an arbitrary aperture antenna in a finite size ground plane as mentioned in this paper, where the boundary value solution considers the pattern component when the aperture is in an infinite ground plane, and the diffraction solution (secondary pattern) considers the contribution to the pattern from the edges of the finite ground plane.
Abstract: The method of combining wedge diffraction solutions for the analysis of an axial TEM-mode slot is extended here for an arbitrary aperture antenna in a finite size ground plane. The new approach, however, considers superposition of boundary-value and wedge-diffraction solutions on the same antenna. The boundary-value solution (primary pattern) considers the pattern component when the aperture is in an infinite ground plane, and the diffraction solution (secondary pattern) considers the contribution to the pattern from the edges of the finite ground plane.
TL;DR: In this paper, an analysis is presented for calculating the backscattered fields of an electromagnetic plane wave by lossless dielectric spheres of arbitrary density using the Watson transformation, which serves to split the exact Mie solution, given as an infinite series, into the geometrical optics fields and the diffracted fields.
Abstract: An analysis is presented for calculating the backscattered fields of an electromagnetic plane wave by lossless dielectric spheres of arbitrary density. This method involves the Watson transformation which serves to split the exact Mie solution, given as an infinite series, into the geometrical optics fields and the diffracted fields. The former comes from the illuminated region of the sphere and may be obtained from the geometrical optics method. The latter comes from the shadow region and consists of two different types of surface waves. One is a "creeping wave" analogous to that of perfectly conducting spheres. The other is a wave which enters the sphere and emerges as a surface wave in the shadow region. This wave is unique to dielectric spheres and is the stronger of the two surface waves. In the widely used geometric optics methods it is assumed that the optics fields are the dominant contributors even though stationary rays which are not in the direction of backscatter must be added in to give a degree of agreement with the exact Mie series results. In this paper we derive the optics fields and show that they differ in some respects from those obtained by the geometric optics method. They are smaller than heretofore assumed and contribute negligibly to the backscatter in this particular range of ka (4-20). Using our rigorous approach we can show the diffracted fields to be the major contributors to the total backscatter. Numerical results for the backscattering cross sections using diffracted and optics fields, and optics fields alone will be presented for relative index of refraction of 1.6. The agreement between our results (diffracted and optics) and exact results from the Mie series is excellent. A subsequent paper will be concerned with the diffracted fields.
TL;DR: In this article, a general numerical technique for analyzing monopole antennas protruding from a conducting sphere is suggested, and the results for special cases of antenna locations are compared to known and approximate solutions showing that the method is practical and accurate.
Abstract: A general numerical technique for analyzing monopole antennas protruding from a conducting sphere is suggested. Computed results for special cases of antenna locations are compared to known and approximate solutions showing that the method is practical and accurate.
TL;DR: In this paper, it is shown that the dominant contributions come from the surface waves rather than the geometrical optics fields in the particular range where the Geometrical Optics Fields have been assumed to be the dominant contributor.
Abstract: In a previous paper we discussed the geometric optics contribution to the scattering from a large dense dielectric sphere. This is a sequel to this paper and treats the more important diffracted wave contribution. The problem of electromagnetic wave scattering by a lossless dielectric sphere is more involved than that for the perfectly conducting sphere, since waves existing within the sphere can contribute significantly. The geometrical optics method which is relatively straightforward has been widely used for solving the problems of large, with respect to wavelength, dielectric spheres. Approximate expressions based on this method have been derived and have indicated that the geometrical optics fields are the major contributor to the total backscattering. However, a rigorous approach [1] based on the Watson transformation which splits the Mie series into two terms, geometrical optics fields and diffracted fields, shows that the former contributes negligibly to the total backscattering in the range ka = 5 to 20 for relative refractive index m = 1.6 . In this paper we confine ourselves to the diffracted fields which give rise to surface waves. It is shown that the dominant contributions come from the surface waves rather than the geometrical optics fields in the particular range where the geometrical optics fields have been assumed to be the dominant contributor. Although a rigorous mathematical analysis associated with the Watson transformation for the scattering problems has been known fundamentally for many years, a complete numerical result based on this transformation has not been available, especially for a dielectric cylinder or sphere. Such results would serve to provide a sound basis for understanding the scattering mechanisms involved and also would serve to check the validity of approximate expressions obtained under a particular assumption. Complete numerical results are included and lead to several interesting conclusions.
TL;DR: For a linear uniform array of n elements, an expression for the directivity as a function of the spacing and the phase constants was derived in this article for the cases of isotropic elements, collinear short dipoles, and parallel short dipole.
Abstract: For a linear uniform array of n elements, an expression is derived for the directivity as a function of the spacing and the phase constants. The cases of isotropic elements, collinear short dipoles, and parallel short dipoles are included. The formula obtained is discussed in some detail and contour diagrams of the directivity as a function of the spacing and the phase constants in the above-mentioned cases are exhibited.
TL;DR: In this article, an extension of Oliner's theory is used to predict the impedance of slots with dielectric coatings, and theoretical curves are presented which show the change in impedance as a function of dielectrics constant, dielectors losses, and dielectoric thickness.
Abstract: An extension of Oliner's theory is used to predict the impedance of slots with dielectric coatings. Theoretical curves are presented which show the change in impedance as a function of dielectric constant, dielectric losses, and dielectric thickness. The effect of a dielectric or plasma upon the resonant frequency is also included. The agreement with experimental dielectric-covered slot data justifies the extension of Oliner's theory.
TL;DR: In this article, the dispersive property of a lossless, isotropic, and homogeneous plasma is used to enhance the resolution of transmitted pulses at the receiver, and an expression is obtained for the carrier phase variation of a rectangular envelope pulse so that the pulse collapses on itself at the receiving node.
Abstract: The compression of frequency-modulated RF pulses is discussed when the dispersive property of a lossless, isotropic, and homogeneous plasma is used to enhance the resolution of transmitted pulses at the receiver. Using the basic concept of group velocity, an expression is obtained for the carrier phase variation of a rectangular envelope pulse so that the pulse collapses on itself at the receiver. Unlike the chirp radar pulse, the frequency variation is not linear and the optimum detection of transmitted pulses depends on both the plasma frequency and the distance between the transmitter and the receiver. The method of convolution was used to obtain numerical results, which indicate that the formulation given results in compression for short propagation distances.
TL;DR: In this article, an integral equation for the current on the surface of the antenna was formulated and subsequently solved by numerical evaluation of associated moment functions in the Fourier transform plane, and the magnitude, but not the distribution, of the current was found to be strongly affected by the presence of the dissipative medium.
Abstract: The input admittance and the current distribution of a finite vertical tubular dipole antenna located above an infinite dissipative half-space can be found as a function of the distance above and the electric properties of the dissipative half-space. An integral equation for the current on the surface of the antenna is formulated and subsequently solved by numerical evaluation of associated moment functions in the Fourier transform plane. The magnitude, but not the distribution, of the current is found to be strongly affected by the presence of the dissipative medium. At certain distances above the half-space, the input conductance of the antenna reaches its maximum value.
TL;DR: In this paper, an analytical and closed-form expression for input admittance was obtained for an annular aperture antenna driven by a coaxial transmission line, and the effect of all higher order TM on to the admittance is found to be quite significant.
Abstract: An annular aperture antenna driven by a coaxial transmission line is studied. An analytical and closed-form expression for input admittance is obtained. The effect of all higher order TM on to the admittance is found to be quite significant. Aperture field distribution is expressed in terms of the TEM and the first five TM on modes. Higher order modes at the aperture can be estimated from the edge behavior. Near-field distribution based upon these modes is then cast into a form suitable for numerical evaluation.
TL;DR: In this paper, a technique is developed to probe the atmospheric turbulence strength and wind velocity along a path using millimeter waves as a tool, using data obtained in a line-of-sight millimeter-wave propagation experiment.
Abstract: A technique is developed to probe the atmospheric turbulence strength C_{n}^{2} and the wind velocity along a path using millimeter waves as a tool. Data obtained in a line-of-sight millimeter-wave propagation experiment are processed and used as the source of information. The averaged C_{n}^{2} and wind velocity together with their gradients along the propagation path are calculated by inverting a set of integral equations. A numerical method is used to yield the least-square-error solutions. Comparison is made between the theoretically calculated wind velocity over a 33-hour period and that measured by a conventional anemometer.