Showing papers in "IEEE Transactions on Antennas and Propagation in 1973"
TL;DR: There are at least three different definitions of cross polarization used in the literature, and the definition which corresponds to one standard measurement practice is proposed as the best choice.
Abstract: There are at least three different definitions of cross polarization used in the literature. The alternative definitions are discussed with respect to several applications, and the definition which corresponds to one standard measurement practice is proposed as the best choice.
895 citations
TL;DR: In this article, a historical summary of the development of microwave absorbing materials and anechoic chambers is presented, along with a detailed discussion of the applications of these materials and their applications.
Abstract: A historical summary of the development of microwave absorbing materials and anechoic chambers is presented.
348 citations
Journal Article•
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TL;DR: In this paper, the authors use a computer program to compute quantities specifying the low frequency scattering behavior of rotationally symmetric bodies which are metallic (electromagnetic scattering), soft, or hard (acoustic scattering).
Abstract: By using a computer program, the authors intend to compute quantities specifying the low frequency scattering behavior of rotationally symmetric bodies which are metallic (electromagnetic scattering), soft, or hard (acoustic scattering)
277 citations
TL;DR: The meander-line polarizer as discussed by the authors consists of several printed-circuit sheets with etched-copper meander lines, spaced about one-quarter wavelength apart, and can be used for medium high-power densities.
Abstract: The meander-line polarizer consists of several printed-circuit sheets with etched-copper meander lines. The sheets are spaced about one-quarter wavelength apart. This communication explains the principle of operation of the polarizer, describes the design procedure, and gives dimensions and performance data of a typical polarizer. For example, an axial ratio of better than 1.5 dB has been obtained over X band. The polarizer can be used for medium high-power densities. A theoretical analysis of dissipation loss and experimental results of high-power tests are presented.
265 citations
TL;DR: In this paper, the authors developed a method for determining the far field pattern of an antenna from probe compensated near-field measurements over the surface of a right circular cylinder enclosing the antenna.
Abstract: 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.
226 citations
TL;DR: In this article, a stepped-septum polarizer was designed that is capable of at least 26 dB of isolation over a 20 percent frequency band, which can be used to excite high purity left or right circular, as well as tilted linear polarizations in a phased array of square waveguides.
Abstract: A stepped-septum polarizer has been designed that is capable of at least 26 dB of isolation over a 20 percent frequency band. The three-port device may be used to excite high purity left or right circular, as well as tilted linear polarizations in a phased array of square waveguides.
210 citations
TL;DR: The possibility of analyzing scattering and antenna problems from a singularity expansion point of view is discussed in this article, where a thin-wire scatterer is considered by first determining the locations of the exterior natural resonant frequencies and then constructing the time response of the current on the body, much in the same manner as in classical circuit theory.
Abstract: In this paper, the possibility of analyzing scattering and antenna problems from a singularity expansion point of view is discussed. As an example of the method, a thin-wire scatterer is considered by first determining the locations of the exterior natural resonant frequencies and then constructing the time response of the current on the body, much in the same manner as in classical circuit theory. The numerical techniques used will be presented, and some advantages of the singularity expansion method over the other conventional ways of treating this problem will be mentioned.
205 citations
TL;DR: In this paper, the cross-polarity of offset reflector antennas was investigated for linearly and circularly polarized excitations with a dual mode feed illuminating an offset paraboloid.
Abstract: The cross polarized radiation for linearly polarized excitation and the beam displacement for circularly polarized excitation have been investigated for offset reflector antennas. Numerical calculations are given to illustrate the dependence upon the angle \theta_{0} between the feed axis and the reflector axis as well as upon the half-angle \theta_{c} subtended at the focus by the reflector. In the case \theta_{0} = \theta_{c} = 45\deg , measured results have been obtained for both linearly and circularly polarized excitations with a dual mode feed illuminating an offset paraboloid. The cross polarized radiation of horn reflector and open Cassegrainian antennas rises sharply to rather high values off the beam axis; however, in general, the maximum cross polarized radiation of offset reflector antennas can be made small by using a small angle between the feed and reflector axes. The cross polarization caused by offset is compared with that caused by an unbalanced feed pattern. The effect of the longitudinal current distribution and of departure of the surface from a paraboloid on cross polarization are also examined. The clarification of these cross polarization properties is found to be valuable in the design of reflector antennas.
167 citations
TL;DR: In this article, a new computer-aided procedure based on the method of modal expansions is presented and applied to the scattering from a periodic structure composed of a perfectly conducting surface.
Abstract: The method of modal expansions is a fundamental technique for solving the electromagnetic boundary value problems. As its practical alogrithm, the point-matching method has been used but frequently failed. A new computer-aided procedure based on the method of modal expansions is presented and applied to the scattering from a periodic structure composed of a perfectly conducting surface. As an example, the scattering from the grating with a sinusoidal height profile is calculated. It is demonstrated numerically that the new procedure leads to desirable results, while the point-matching method does not. Several physical characteristics on the reflection grating including the diffraction anomalies are explored.
135 citations
TL;DR: In this paper, a generalized three-antenna approach is proposed for determining power gain and polarization of antennas at reduced range distances, and the required data are obtained by an extrapolation technique which includes provisions for rigorously evaluating and correcting for errors due to proximity and multipath interference effects.
Abstract: A new technique is described for determining power gain and polarization of antennas at reduced range distances. It is based on a generalized three-antenna approach which, for the first time, permits absolute gain and polarization measurements to be performed without quantitative a priori knowledge of the antennas. The required data are obtained by an extrapolation technique which includes provisions for rigorously evaluating and correcting for errors due to proximity and multipath interference effects. The theoretical basis provides a convenient and powerful approach for describing and solving antenna measurement problems, and the experimental method employed illustrates the utility of this approach. Examples of measurements are included which exhibit errors in gain as small as \pm0.11 dB ( 3\sigma ).
128 citations
TL;DR: In this article, the authors present a map based upon the ratio of the strengths of the firstorder contributions to the backscatter spectrum (the approach-recede first-order Bragg lines) and compare qualitatively with a U. S. Weather Bureau map of the area.
Abstract: This work presents preliminary results on attempts to map winds of a storm at long range (500 to 1000 nmi) over a large area ( 10^{5} mi2) in the North Atlantic from the U. S. Naval Research Laboratory, HF radar research facilities at Chesapeake Beach, Md. [1] It appears that the short time response of the sea surface to local winds can be mapped by the analysis of a matrix of range-azimuth records containing frequency power spectra of HF radar signals backscattered from the sea surface via the ionosphere. This paper presents such a map based upon the ratio of the strengths of the first-order contributions to the backscatter spectrum (the approach-recede first-order Bragg lines) and is compared qualitatively with a U. S. Weather Bureau map of the area.
TL;DR: In this article, the first horn described covers the frequency range from 1.0-12.0 GHz with the flared portion of the horn having an axial length of 6 in as compared with 12 in for an earlier model.
Abstract: Ever-increasing antenna frequency bandwidth requirements for countermeasures applications and electromagnetic compatibility measurements have provided the impetus for the development of a series of very broad-band horns. In addition to the broad bandwidth, a substantial reduction in axial length over that of earlier models has been achieved for the two designs discussed in this communication. The first horn described covers the frequency range from 1.0-12.0 GHz with the flared portion of the horn having an axial length of 6 in as compared with 12 in for an earlier model. Although horn antennas are not commonly considered for use at frequencies as low as 0.2 GHz, the short axial length design appeared to be an attractive approach in developing a very reasonably sized antenna operating in the 0.2-2.0 GHz range. The technique of fabricating the H plane walls in the form of a grid was used in both designs as a means of maintaining the required H -plane half-power beamwidths. The grid for the 1.0-12.0 GHz horn is of printed circuit form while the grid elements of the lower frequency horn are made of aluminum tubing. Electrical characteristics of both designs are presented, as well as some additional data for recent advances which indicate that a further reduction in axial length or an increase in bandwidth can be achieved with only a moderate rise in VSWR in the lower portion of the frequency range.
TL;DR: In this paper, the authors developed an asymptotic theory for inhomogeneous wave fields in lossless media, to be termed evanescent fields, and applied it to two-dimensional scattering of an incident plane wave by a curved boundary in a homogeneous medium.
Abstract: The conventional asymptotic theory for propagation of high-frequency fields is based on a local description in terms of homogeneous plane waves A(r) exp [ik_{0}S(r)] , where k_{0} is the (large) free space wavenumber, A(r) is a spatially dependent amplitude, and the phase S(r) is real. The conventional theory does not accommodate the more general class of fields that behave locally like inhomogeneous plane waves with complex phase S(r)= R(r) + iI(r) , where R determines the propagation of the equiphase surfaces and I describes the attenuation. This paper develops an asymptotic theory for inhomogeneous wave fields in lossless media, to be termed evanescent fields. Such fields are encountered, for example, in connection with Gaussian beams and with phenomena on the exterior of surface wave structures or on the dark side of caustics. The scalar wave equation is used to derive eikonal and transport equations for S and A , respectively, and it is shown how the latter equations may be integrated with the aid of trajectories tangent to the direction of
ablaR , which differs slightly from that for the local power flow. Detailed application of the theory is made to two-dimensional scattering of a weakly evanescent incident plane wave by a curved boundary in a homogeneous medium. The phase propagation paths for the reflected field are determined explicitly and are found to possess curvature and points of inflection; these characteristics are shown to be predictable from basic attributes of evanescent wave propagation. For the special case of a circular cylinder, the subsequently constructed reflected field is found to agree with the asymptotic expansion of the rigorous solution, thereby confirming the validity of the theory for weakly evanescent fields. The rigorous solution, valid for arbitrary evanescent decay and obtained from known results for ordinary plane wave scattering by analytic continuation of the incidence angle to complex values, reveals that both the reflected and creeping wave fields should be viewed in a restrictive manner when the evanescent decay is large. However, for weak evanescent decay, these fields retain their customary significance and permit their construction by local evanescent field tracking. It is interesting to observe that in contrast to the nonevanescent case, the creeping waves provide a field contribution exceeding that of the incident or reflected waves in certain portions of the illuminated region.
TL;DR: In this article, a comparison between the antenna pattern comparison technique and the free-space voltage standing-wave ratio technique for evaluating the reflectivity level of radio anechoic chambers is presented.
Abstract: A comparison between the antenna-pattern comparison technique and the free-space voltage standing-wave ratio technique for evaluating the reflectivity level of radio anechoic chambers is presented. Based on an analysis of the two techniques, it is pointed out which parameters influence the measured value of the reflectivity level. The comparison is illustrated with experimental results and it is explained why inconsistent and uncorrelated results may be found when the two methods are used. Furthermore, it is demonstrated, by introducing improvements in a chamber, how the reflectivity level can be used to measure the improvements. This work is inspired by the current discussion of finding a figure of merit for anechoic chambers. Based on the results, an evaluation procedure for anechoic chambers is indicated. However, it is pointed out and illustrated by examples that further investigations are necessary before a satisfactory procedure can be outlined.
TL;DR: In this paper, experiments were described for determining the distributions of current, the driving point impedance, and the electromagnetic fields characteristic of dipole antennas immersed in the sea near the surface.
Abstract: Experiments are described for determining the distributions of current, the driving-point impedance, and the electromagnetic fields characteristic of dipole antennas immersed in the sea near the surface. Measured and theoretical results are compared at two frequencies with good agreement.
TL;DR: In this paper, the impedance properties of a waveguide longitudinal slot antenna of arbitrary length and offset in guide walls of finite thickness were investigated by treating the slot discontinuity as an electromagnetic boundary value problem and the resulting pair of coupled integral equations were solved by numerical techniques.
Abstract: The impedance properties of a waveguide longitudinal slot antenna of arbitrary length and offset in guide walls of finite thickness are investigated. These properties are obtained by treating the slot discontinuity as an electromagnetic boundary value problem and the resulting pair of coupled integral equations are solved by numerical techniques. Results are given for slots having lengths from 0.35\lambda to 1.7\lambda and are in good agreement with experimental results.
TL;DR: A tutorial review of techniques used for the measurement of near-fields of antennas and scatterers, and an extensive bibliography of the readily available literature in this area, are presented in this paper.
Abstract: A tutorial review of techniques used for the measurement of near-fields of antennas and scatterers, and an extensive bibliography of the readily available literature in this area, are presented.
TL;DR: Among the several algorithms examined, the method of dynamic programming produced the lowest peak sidelobe on the average, and the compactness of the random distribution almost guarantees against selection of a random array with catastrophically large peak sidelobes.
Abstract: Thinned arrays (mean interelement spacing greater than one-half wavelength) are made aperiodic to suppress grating lobes. Many thinning algorithms were created in the 1960's and tested by computer simulation. Seventy such algorithmically designed aperiodic arrays are examined and the distribution of their peak sidelobes, relative to the expected values for random arrays having the same parameters, is obtained. The distribution is compared to that of a set of 170 random arrays. Both distributions are found to be nearly log normal with the same average and median values. They differ markedly in their standard deviations, however, the standard deviation of the random array distribution (1.1 dB) is approximately half that of the algorithmic group. The compactness of the random distribution almost guarantees against selection of a random array with catastrophically large peak sidelobes. Among the several algorithms examined, the method of dynamic programming produced the lowest peak sidelobe on the average.
TL;DR: In this paper, a method for diffraction of electromagnetic waves by gratings, in the case of infinite conductivity, is presented. But the method is not suitable for numerical computations.
Abstract: The method previously proposed to investigate the diffraction of electromagnetic waves by gratings, in the case of an infinite conductivity is developed. This method, based on the properties of the analytic functions, allows the solution of theoretical problems and reduces the determination of the efficiencies to the study of differential systems. Some examples show its utility for numerical computation. Good agreement is observed in comparing with the results obtained from other techniques (integral equations).
TL;DR: In this paper, the mean square angular divergence of the beam, the beam cross-section, and the power received by a planar aperture in the medium and the mutual coherence function were investigated.
Abstract: Transport methods have been employed to study the propagation of a narrow-angle electromagnetic beam through a turbulent plasma. Results are presented for the mean-square angular divergence of the beam, the beam cross section, and the power received by a planar aperture in the medium and the mutual coherence function. The problem of backscattered radiation is also considered and results are obtained which reduce, in the limit of zero true absorption, to previous results.
Abstract: Strong cosmic radio sources provide a constant broadband and accurately positioned test transmitter for measurements of large antennas. Some sources have their flux density determined absolutely and can be used to calibrate the antenna gain. This paper presents up-to-date data on the radio sources which are useful for antenna measurements. The measurement of pointing and focusing corrections is discussed. The main part of the paper is concerned with the derivation of major antenna parameters such as aperture and beam efficiency, beam solid angle, sidelobe levels, error pattern characteristics from measurements on radio sources. The effects of a finite angular source size are discussed, and it is shown how measurements on sources of different size increase the information on the derived antenna parameters. The methods to measure very weak sidelobes are treated and the external factors, solar and galactic radiations influence of the earth and atmosphere, which might limit the accuracy of the measurement are described. The paper takes a practical approach to the subject and contains graphs with numerical data.
TL;DR: In this paper, the consequences of nonuniqueness for integral equations used in the numerical resolution of electromagnetic scattering problems are investigated from a practical point of view, where the scatterers are closed perfectly conducting cylinders of arbitrary cross section illuminated by a plane wave in both E and H polarizations.
Abstract: The consequences of nonuniqueness for integral equations used in the numerical resolution of electromagnetic scattering problems are investigated from a practical point of view. The scatterers are closed perfectly conducting cylinders of arbitrary cross section illuminated by a plane wave in both E and H polarizations. It is shown how to detect the frequencies at which nonuniqueness occurs, and how to avoid the resulting errors by the use of the notion of an equivalent problem. This approach is compared to other ones proposed by different authors. A new interpretation of the computed solution, when uniqueness conditions are not satisfied, is given and it is shown how to use such a solution in the computation of the resonant modes of the interior problem, even for degenerate modes.
TL;DR: In this paper, the authors describe the spatial filtering effect of intermodulation products in an active phased array (AHA) and demonstrate the main-beam directions of beams formed by third and fifth-order intermodulations.
Abstract: In an active phased array (i.e., an array that has amplifiers in each element) transmitting multiple beams, the intermodulation products generated by the amplifier amplitude nonlinearities form beams that, in general, radiate in directions different from the principal beam directions. In effect, the phased array antenna spatially filters the intermodulation products formed by signals from different beams. In a communications application this effect can be used to reduce the signal-to-intermodulation interference ratio. A description of this phenomenon is given and examples are presented that illustrate the mainbeam directions of beams formed by third- and fifth-order intermodulation products. An experiment that was performed to demonstrate this effect is described. The spatial filtering effect for beams with amplitude modulated signals is also treated, with an improvement in carrier-to-intermodulation ratio theoretically demonstrated.
TL;DR: In this article, a two-dimensional density is constructed from given marginals and a given correlation coefficient by using an expansion in orthogonal polynomials, and the results are used to derive a general method of finding the field scattered by a rough surface by both physical and geometrical optics when the surface is generated by a stationary random process which is not necessarily normal.
Abstract: A two-dimensional density is constructed from given marginals and a given correlation coefficient by using an expansion in orthogonal polynomials. The results are used to derive a general method of finding the field scattered by a rough surface by both physical and geometrical optics when the surface is generated by a stationary random process which is not necessarily normal. The example of an exponential surface is calculated in more detail, particularly for backscatter.
TL;DR: In this paper, the Stokes parameters of a point on the surface of the poincare sphere were used to represent the polarization state of fully polarized electromagnetic fields, and a simple formula was derived for calculating the power received by an antenna illuminated by a partially polarized wave.
Abstract: The use of points on the surface of the poincare sphere to represent the polarization state of fully polarized electromagnetic fields is extended to partially polarized fields by representing their polarization by points inside the sphere. The coordinates of a point \bar{W} representing the polarization state are shown to be simply related to the Stokes parameters. The center of the sphere represents a completely unpolarized wave, and the degree of polarization is given by the distance of the point \bar{W} from the center of the sphere. A simple formula is derived for calculating the power received by an antenna illuminated by a partially polarized wave. A method is described for measuring the polarization state by a number of intensity measurements.
TL;DR: In this paper, the edge currents derived from the edge diffraction theory for a halfplane were used to obtain the radiation patterns of a parabeloidal reflector antenna when illuminated by a source at the focus.
Abstract: Equivalent edge currents, derived from the edge diffraction theory for a half-plane, are used to obtain the radiation patterns of a parabeloidal reflector antenna when illuminated by a source at the focus. Cylindrical wave diffraction coefficients are used. The method avoids infinities at caustics and shadow boundaries thus giving solutions which are finite everywhere. A slope-wave equivalent current correction term is applied when the illumination is tapered towards the edge of the reflector. Comparisons are given with the physical optics approach and experimental results.
TL;DR: Theoretical and experimental investigations on coaxial feeds excited by H 11 modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them as mentioned in this paper.
Abstract: Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H 11 modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of 100\deg to 160\deg . Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.
TL;DR: The beam-pointing error of an (M + 1) \times (N - 1) planar phased array is analyzed by the use of both analytical and Monte Carlo techniques.
Abstract: The beam-pointing error of an (M + 1) \times (N + 1) planar phased array is analyzed by the use of both analytical and Monte Carlo techniques. Simple formulas for the rms pointing error are obtained for uniform planar arrays with both uniform and Gaussian uncorrelated phase-error distributions and for any arbitrary scan angle.
TL;DR: In this article, simple quadratic forms were derived for the self and mutual-admittances of delta gaps in thin wire structures in terms of the characteristic currents of the structures.
Abstract: Particularly simple quadratic forms are derived for the self- and mutual-admittances of delta gaps in thin wire structures in terms of the characteristic currents of the structures. Results based on these forms are found to be in substantial agreement with those derived by other methods.
TL;DR: The multiprobe reflector can perform the measurements usually performed with the slotted line without the need for mechanical adjustment, thus making it ideal for automated systems and avoiding the use of adaptors with their attendant errors.
Abstract: The multiprobe reflector can perform the measurements usually performed with the slotted line without the need for mechanical adjustment, thus making it ideal for automated systems. Theory is presented showing how impedance data may be obtained from three or more arbitrarily placed probes; the spacing need not be at any particular fraction of a wavelength thus permitting very wide band operation. The use of additional probes permits measurement of frequency and also self checking of the system, thus providing accuracies comparable with the best slotted lines available. The simplicity of the hardware makes it easy to install in both standard and non-standard waveguides and transmission lines thus avoiding the use of adaptors with their attendant errors. A brief error analysis is included. Measurements of antenna impedance and wall loss, using a nonstandard size of waveguide, are presented and show an accuracy comparable with the best slotted lines.