Showing papers in "IEEE Transactions on Antennas and Propagation in 1982"
TL;DR: In this paper, the electric field integral equation (EFIE) is used with the moment method to develop a simple and efficient numerical procedure for treating problems of scattering by arbitrarily shaped objects.
Abstract: The electric field integral equation (EFIE) is used with the moment method to develop a simple and efficient numerical procedure for treating problems of scattering by arbitrarily shaped objects. For numerical purposes, the objects are modeled using planar triangular surfaces patches. Because the EFIE formulation is used, the procedure is applicable to both open and closed surfaces. Crucial to the numerical formulation is the development of a set of special subdomain-type basis functions which are defined on pairs of adjacent triangular patches and yield a current representation free of line or point charges at subdomain boundaries. The method is applied to the scattering problems of a plane wave illuminated flat square plate, bent square plate, circular disk, and sphere. Excellent correspondence between the surface current computed via the present method and that obtained via earlier approaches or exact formulations is demonstrated in each case.
4,835 citations
TL;DR: A beamforming structure is presented which can be used to implement a wide variety of linearly constrained adaptive array processors and is shown to incorporate algorithms which have been suggested previously for use in adaptive beamforming as well as to include new approaches.
Abstract: A beamforming structure is presented which can be used to implement a wide variety of linearly constrained adaptive array processors. The structure is designed for use with arrays which have been time-delay steered such that the desired signal of interest appears approximately in phase at the steered outputs. One major advantage of the new structure is the constraints can be implemented using simple hardware differencing amplifiers. The structure is shown to incorporate algorithms which have been suggested previously for use in adaptive beamforming as well as to include new approaches. It is also particularly useful for studying the effects of steering errors on array performance. Numerical examples illustrating the performance of the structure are presented.
1,923 citations
TL;DR: In this paper, a moment method solution to the problem of input impedance and mutual coupling of rectangular microstrip antenna elements is presented, which uses the grounded dielectric slab Green's function to account rigorously for the presence of the substrate and surface waves.
Abstract: A moment method solution to the problem of input impedance and mutual coupling of rectangular microstrip antenna elements is presented. The formulation uses the grounded dielectric slab Green's function to account rigorously for the presence of the substrate and surface waves. Both entire basis (EB) and piecewise sinosoidal (PWS) expansion modes are used, and their relative advantages are noted. Calculations of input impedance and mutual coupling are compared with measured data and other calculatious.
714 citations
TL;DR: Conventional adaptive beamformers utilizing some form of automatic minimization of mean square error exhibit signal cancellation phenomena when adapting rapidly, and Widrow has devised a different solution to the problem: to move the receiving array spatially to modulate emanations received off the look direction, without distorting useful signals incident from theLook direction.
Abstract: Conventional adaptive beamformers utilizing some form of automatic minimization of mean square error exhibit signal cancellation phenomena when adapting rapidly. These effects result from adaptive interaction between signal and interference, when signal and interference are received simultaneously. Similar phenomena have been observed and analyzed in relatively simple adaptive noise cancelling systems. A study of these phenomena in the simpler systems is used to provide insight into similar behavior in adaptive antennas. A method for alleviating signal cancellation has been devised by Duvall, whereby the signal components are removed from the adaptive process, then reinserted to form the final system output. Widrow has devised a different solution to the problem: to move the receiving array spatially (or electronically) to modulate emanations received off the look direction, without distorting useful signals incident from the look direction. This approach is called "spatial dither" and introduces the additional possibility of modulating "smart" jammer signals, thereby limiting their effectiveness.
328 citations
TL;DR: In this article, a planar line antenna array and optical system for imaging has been developed by using a reverse-microscope optical configuration and a modified bow-tie antenna design, which eliminates the troublesome effects of substrate surface waves.
Abstract: Many millimeter and far-infrared imaging systems are limited in sensitivity and speed because they depend on a single scanned element. Because of recent advances in planar detectors such as Schottky diodes, superconducting tunnel junctions, and micro-boiometers, an attractive approach to this problem is a planar antenna array with integrated detectors. A planar line antenna array and optical system for imaging has been developed by the authors. The significant advances are a "reverse-microscope" optical configuration and a modified bow-tie antenna design. In the "reverse-microscope" configuration, a lens is attached to the bottom of the substrate containing the antennas. Imaging is done through the substrate. This configuration eliminates the troublesome effects of substrate surface waves. The substrate lens has only a single refracting surface, making possible a virtually aplanatic system, with little spherical aberration or coma. The array is characterized by an optical transfer function that is easily measured. An array with 19 dB crosstalk levels between adjacent antennas has been tested and it was found that the array captured 50 percent of the available power. This imaging system was diffraction limited.
288 citations
TL;DR: In this article, the design of a microstrip antenna covered with a dielectric layer is presented, where the effect of loading on the resonant frequency of the antenna is considered.
Abstract: The design of a microstrip antenna covered with a dielectric layer is presented. Due to loading, the resonant frequency of the antenna changes. The absolute value of the change increases with the operating frequency, the relative permittivity (except plasma), and the thickness of the dielectric layer. This change may cause degradation in performance due to the inherent narrow bandwidth of microstrip antennas if the effect of loading is not considered in the design. The curves presented here may be used to design microstrip antennas that may be subjected to icing or a plasma environment or coated with protective layers. Numerical and experimental results for the fractional change in the resonant frequency are round to be in good agreement.
231 citations
Abstract: A simple closed-form approximate solution is given for the transmission coefficient of a normally incident electromagnetic plane wave through a screen made of periodic metal grids (inductive screen), or made of metal plates (the complementary capacitive screen). Explicit formulas are also presented for cascading screens and dielectric slabs. When compared with the exact solution, our approximate simple formulas show good numerical accuracy.
228 citations
TL;DR: In this article, it is shown that even if it is known that the source is spherically symmetric, it is not possible to determine its radial structure, apart from a constant amplitude and a finite radius.
Abstract: The fields radiated by spherically symmetric time-harmonic sources are used to illustrate how little can be learned about a source from knowledge of the radiated field outside of the source volume. It is shown that even if it is known that the source is spherically symmetric, it is not possible to determine its radial structure. Moreover, even if the radial structure of the source is known apart from a constant amplitude and a finite radius, it is not possible to evaluate those two unknowns independently. These examples are applied to demonstrate explicitly that two methods that have been claimed to produce exact unique solutions to inverse-source and inverse-scattering problems do not yield the claimed results.
193 citations
TL;DR: In this paper, a heuristic discussion of the radiation properties of the transverse magnetic (TM 11 ) and (TM 12 ) modes of the annular-ring microstrip antenna is presented.
Abstract: A heuristic discussion of the radiation properties of the transverse magnetic (TM 11 ) and (TM 12 ) modes of the annular-ring microstrip antenna is presented, indicating the possibility of the TM 12 mode as a superior microstrip antenna. Rigorous analyses of the resonant frequency characteristics of the antenna are then performed with the matched asymptotic expansions technique and the perturbation approach. The analyses show that the TM 12 mode is decidedly the best mode for microstrip antenna applications while the TM 11 mode, having a high Q -factor, is best reserved for resonator applications. The analyses include the study of the resonant frequencies, bandwidths, and radiation pattern of the antenna. The matched asymptotic expansions technique and the perturbation approach are also shown to agree excellently with each other within their domain of validity.
175 citations
TL;DR: In this paper, a rigorous analysis of the resonant frequency characteristics of an annular ring conductor printed on a dielectric substrate backed by a ground plane is presented, where the problem is cast into a set of vector dual integral equations by using vector Hankel transform (VHT).
Abstract: A rigorous analysis of the resonant frequency characteristics of an annular-ring conductor printed on a dielectric substrate backed by a ground plane is presented. The problem is cast into a set of vector dual integral equations by using vector Hankel transform (VHT). Galerkin's method is then applied to compute the resonant frequencies of both transverse magnetic modes (TM 11 and TM 12 ) of the microstrip antenna. The real part of the resonant frequency shift of the TM 11 mode increases with increasing dielectric thickness in contrast to the TM 12 mode. While the TM 11 mode has a high Q , it is a poor radiating mode; the TM 12 mode is more suitable for antenna applications. For a probe excitation the input impedance is obtained using single mode approximation for both the TM 11 and TM 12 modes. It is shown that the TM 12 mode of the annular ring has a greater bandwidth than the TM 11 mode.
137 citations
TL;DR: In this paper, the authors derived an expression for the input impedance of a rectangular microstrip antenna excited by either a microstrip line or a coaxial probe using the reaction integral equation.
Abstract: Using Richmond's reaction integral equation, an expression is derived for the input impedance of microstrip patch antennas excited by either a microstrip line or a coaxial probe. The effects of the finite substrate thickness, a dielectric protective cover, and associated surface waves are properly included by the use of the exact dyadic Green's function. Using the present formulation the input impedance of a rectangular microstrip antenna is determined and compared with experimental and earlier calculated results.
TL;DR: In this paper, the physical optics approximation is applied to the acoustic and electromagnetic direct scattering integral representation, yielding an inverse scattering identity which relates the characteristic function of a scatterer to the three-dimensional spatial Fourier transform of the augmented far-field scattering amplitude.
Abstract: The physical optics approximation is applied to the acoustic and electromagnetic direct scattering integral representation, yielding an inverse scattering identity which relates the characteristic function of a scatterer to the three-dimensional spatial Fourier transform of the augmented far-field scattering amplitude. This identity requires full scattering information for all frequencies and aspect angles. An integral equation for incomplete scattering information for this identity is developed. This integral equation is for the unknown characteristic function of the scatterer in terms of the known incomplete scattering information. The kernel of this integral equation is the three-dimensional spatial Fourier transform of the known characteristic function of the scattering information aperture. A regularized analytic closed-form solution to this integral equation is obtained. Synthesized numerico-experimental results verifying this solution are presented. The details of some special cases, consisting of a priori knowledge about the scatterer or the scattering information aperture, are presented.
TL;DR: In this article, the problem of a microstrip antenna covered by a dielectric is formulated in terms of coupled integro-differential equations with the current distribution on the microstrip patch as an unknown variable.
Abstract: The problem of a microstrip antenna covered by a dielectric is formulated in terms of coupled integro-differential equations with the current distribution on the microstrip patch as an unknown variable. Galerkin's method is used to solve for the unknown patch current. Using the present formulation the resonant frequency and bandwidth of a rectangular microstrip antenna are determined and compared with experimental results.
TL;DR: In this article, the theory of operation for a terrain-sensitive propagation path loss model based upon the geometrical theory of diffraction, modified for finite conductivity and local surface roughness, is offered.
Abstract: The theory of operation for a terrain-sensitive propagation path loss model based upon the geometrical theory of diffraction, modified for finite conductivity and local surface roughness, is offered. An evaluation of this new model's performance with respect to the contemporary Longley-Rice point-to-point model is provided by comparisons of modeled and measured data.
TL;DR: Tapered dielectric rod antennas of rectangular cross section were developed for possible application in millimeter-wave Dielectric integrated circuits in this paper, where design principles for a maximum gain design were described, and an example was given.
Abstract: Tapered dielectric rod antennas of rectangular cross section are developed for possible application in millimeter-wave dielectric integrated circuits. Design principles for a maximum gain design are described, and an example is given. Experimental results for antennas designed for low sidelobes and for maximum gain are presented.
TL;DR: In this paper, a hybrid technique combining the frequency-domain method of moments (MM) and the finite-difference time-domain (FD-TD) method is presented for the direct modeling of electromagnetic penetration problems.
Abstract: An approach is presented for the direct modeling of electromagnetic penetration problems which involves a hybrid technique combining the frequency-domain method of moments (MM) and the finite-difference time-domain (FD-TD) method. The hybriding is based upon a novel use of a field equivalence theorem due to Schelkunoff, which permits a field penetration problem to be analyzed in steps by treating the relatively simple external region and the relatively complex internal region separately. The method involves first, determination of an equivalent short-circuit current excitation in the aperture regions of the structure using MM for a given external illumination. This equivalent current excitation over the aperture is next used to excite the complex loaded interior region, and the penetrating fields and induced currents are computed by the FD-TD method. A significant advantage of this frequency domain/time domain hybriding is that no Green's function need be calculated for the interior region. This hybrid approach takes advantage of the ability of MM to solve exterior problems using patch models and also takes advantage of the ability of FD-TD to model in great detail localized space regions containing metal structures, dielectrics, permeable media, anisotropic or nonlinear media, as well as wires.
TL;DR: In this paper, the statistics of scintillation intensity on an X-band satellite downlink obtained using the orbital test satellite beacon transmissions were analyzed and the experimentally found distribution is shown to depart significantly from the expected log-normal distribution, and this is explained in terms of a Gaussian process with a time variable standard deviation from which a universal model is derived.
Abstract: Extensive experimental results are presented on the statistics of tropospheric amplitude scintillations on an X -band satellite down-link obtained using the orbital test satellite beacon transmissions. The experimentally found distribution is shown to depart significantly from the expected log-normal distribution, and this is explained in terms of a Gaussian process with a time variable standard deviation from which a universal model is derived. It has been found that on average no less than about 100 h of data are required before the probability density and cumulative probability distribution functions approach stationarity. The statistics of the scintillation intensity are also presented, and a log-normal distribution of intensity is shown to be in good agreement with observations from other experimental sites. Link budget implications are outlined together with a simple strategy for the investigation of the scintillation process at any ground station.
TL;DR: In this paper, the problem of an electrically small aperture in a conducting screen backed by a conducting body is analyzed and it is found that aperture-body resonances can occur for which the power transmitted through the aperture backed by the body is much larger than that when the body was not present.
Abstract: The problem of an electrically small aperture in a conducting screen backed by a conducting body is analyzed. It is found that aperture-body resonances can occur for which the power transmitted through the aperture backed by a conducting body is much larger than that when the body is not present. An example is an electrically small aperture resonated by a capacitor across its midpoint. In the loss-free case, the transmission cross section of a small resonated aperture is 3\lambda^{2}/4\pi independent of the size or shape of the aperture. For actual conductors, the transmission cross section will be increasingly reduced by conduction loss as the aperture is made smaller.
TL;DR: In this article, it was confirmed that the equivalent radius of a narrow conducting strip is one-fourth its width, and the analysis proceeds from the integral equation for the surface current density induced on a conducting cylinder of general cross section.
Abstract: By means of a simple and direct analytical procedure, it is confirmed that the equivalent radius of a narrow conducting strip is one-fourth its width. The analysis proceeds from the integral equation for the surface current density induced on a conducting cylinder of general cross section and its incorporates knowledge of the current density induced on a narrow strip. Explicit expressions are given for the total axial current induced on the narrow strip and for its echo width.
TL;DR: In this paper, the strong fluctuation random medium theory is applied to calculate scattering from a half-space of dielectric mixture and the first and second moments of the fields are calculated, respectively, by using the bilocal and the distorted Born approximations, and the low frequency limit is taken.
Abstract: The strong fluctuation random medium theory is applied to calculate scattering from a half-space of dielectric mixture. The first and second moments of the fields are calculated, respectively, by using the bilocal and the distorted Born approximations, and the low frequency limit is taken. The singularity of the dyadic Green's function is taken into account. Expressions for the effective permittivity for the full space case are derived. It is shown that the derived result of the effect permittivity is identical to that of the Polder and van Santern mixing formula. The correlation function of the random medium is obtained by using simple physical arguments and is expressed in terms of the fractional volumes and particle sizes of the constituents of the mixture. Backscattering coefficients of a half-space dielectric mixture are also calculated. Numerical results of the effective permittivity and backscattering coefficients are illustrated using typical parameters encountered in microwave remote sensing of dry and wet snow. It is also shown that experimental data can be matched with the theory by using physical parameters of the medium as obtained from ground truth measurements.
TL;DR: In this article, the authors presented two computer programs for computing the mutual coupling at a single frequency between any two antennas arbitrarily oriented and separated in free space, and showed that in most cases the spectrum integration need cover only the solid angle mutually subtended by the smallest spheres circumscribing the antennas.
Abstract: The theory, techniques, details of the important equations, and description of two computer programs are presented for calculating efficiently the mutual coupling at a single frequency between any two antennas arbitrarily oriented and separated in free space. Both programs emphasize efficiency and generality, and require, basically, the complex electric far field of each antenna, and the Eulerian angles designating the relative orientation of each antenna. Multiple reflections between the antennas are neglected but no other restrictive assumptions are involved. If an electric field component is desired instead of coupling, the receiving antenna is replaced by a virtual antenna with uniform far field. The first computer program computes coupling (or fields) versus transverse displacement of the antennas in a plane normal to their axis of separation. An efficient fast Fourier transform (FFT) program was made possible by "collapsing" the far-field input data and showing that inmost cases the spectrum integration need cover only the solid angle mutually subtended by the smallest spheres circumscribing the antennas. Limiting the integration to this solid angle artifically band limits the coupling function, thereby allowing much larger integration increments and reducing run times and storage requirements to a feasible amount for electrically large antennas. The second program is based on a spherical wave representation of the coupling function and rapidly computes coupling (or fields) versus separation distance between the antennas. The spherical wave representation emerged naturally from an intriguing characteristic proven for the mutual coupling function; it, like each rectangular component of electric and magnetic field in free space, satisfies the homogeneous wave equation.
TL;DR: In this article, the phase distribution of a linear array of discrete sources for a specified radiation pattern and a fixed aperture amplitude function is determined by transforming the finite series representing the array factor into an infinite series each term in the form of an integral.
Abstract: The method of determination of the phase distribution of a linear array of discrete sources for a specified radiation pattern and a fixed aperture amplitude function is presented. The finite series representing the array factor is transformed into an infinite series each term of which is in the form of an integral. Synthesis is carried out from asymptotic evaluation of the integral by the stationary phase method. Computed results for sector and cosecant beam are presented.
TL;DR: In this paper, the least mean square pattern synthesis method is extended to include constraints such as pattern nulls or pattern-derivative nulls at a given set of angles.
Abstract: The least mean square pattern synthesis method is extended to include constraints such as pattern nulls or pattern-derivative nulls at a given set of angles. The problem is formulated as a constrained approximation problem which is solved exactly, and a clear geometrical interpretation of the solution in a multidimensional vector space is given. The relation of the present method to those of constrained gain maximization and signal-to-noise ratio (SNR) maximization is discussed and conditions for their equivalence stated. For a linear uniform N -element array it is shown that, when M single nulls are imposed on a given "quiescent" pattern, the optimum solution for the constrained pattern is the initial pattern and a set of M -weighted (\sin Nx)/\sin x -beams. Each beam is centered exactly at the corresponding pattern null, irrespective of its relative location. For the case of higher order nulls, the n th pattern derivative is similarly canceled by the n th derivative of a (\sin Nx)/\sin x -beam. In addition, simple quantitative expressions are derived for the pattern change and gain cost associated with the forced pattern nulls. Several illustrative examples are included.
TL;DR: In this paper, a method of designing series-fed microstrip patch arrays to produce a shaped pattern is described, based on a circuit representation of the patches in the array environment with experimentally determined parameters.
Abstract: A method of designing series-fed microstrip patch arrays to produce a shaped pattern is described. The technique is based on a circuit representation of the patches in the array environment with experimentally determined parameters. The positions and widths of the patches are derived from the amplitudes and phases of the elements of a uniform array, which produces the desired pattern and which has the same extent as the patch array. For the array to have high efficiency, the amplitude distribution mast not be strongly peaked. An algorithm for obtaining an approximation to the desired far-field amplitude distribution while retaining control over the amplitude of excitatian is presented. Very close agreement has been obtained between calculated and measured performance of such arrays.
TL;DR: In this article, an expression for the complex admittance of a radiating slot in the ground plane of a microstripline is obtained from the complex radiated power and discontinuity in the modal voltage.
Abstract: An expression for the complex admittance of a radiating slot in the ground plane of a microstripline is obtained from the complex radiated power and discontinuity in the modal voltage. The complex radiated power is obtained from the angular spectrum of plane waves. The electric field distribution in the microstripline, required for the determination of the discontinuity in the modal voltage, is determined from the analysis presented by Yamashita and Atsuki. The theoretical results are compared with experimental data.
TL;DR: In this article, a spectral-iteration approach for analyzing the problem of scattering from periodically perforated screens which find useful applications as radomes, optical filters, artificial dielectrics, and so on is applied.
Abstract: A novel technique, called the spectral-iteration approach, for analyzing the problem of scattering from periodically perforated screens which find useful applications as radomes, optical filters, artificial dielectrics, and so on is applied. The formulation is carried out in the spectral domain where a set of algebraic equations is obtained directly for the spectral coefficients of the aperture field distribution (or the induced current density) rather than via an integral equation formulation. These equations are then solved simultaneously using an iterative procedure developed in this paper that circumvents the need for matrix inversion. Because the matrix solution is avoided in the spectral approach, it is capable of handling large aperture sizes in a computationally efficient manner. The efficiency of computation results from the use of the fast Fourier transform (FFT) algorithm which is employed in the derivation of the algebraic equations and in the iteration procedure. A unique feature of the spectral-iteration approach is that it has a built-in boundary-condition check which provides a reliable indication of the accuracy of the solution. It is also shown that the spectral domain technique can be applied to even a wider class of geometries, e.g., the step discontinuity in a waveguide.
TL;DR: The adaptive array performance is dominated by this coefficient and can be improved by properly choosing the first three factors, and several examples on the selection of element placement in adaptive arrays are presented.
Abstract: A receiving array antenna can steer its main beam toward any direction by adjusting the complex weight in each element. However it cannot always steer one beam and one null toward two prespecified directions simultaneously with a single set of weights. The ability for an array to steer one beam and one or more nulls simultaneously is determined by five factors: 1) element positions, 2) orientations of elements, 3) antenna patterns of elements, 4) polarizations of signals, and 5) directions of the beams and/or nulls. A coefficient is defined, called spatial correlation, which includes these factors and completely characterizes array beam pointing and nulling. Its application to adaptive arrays is demonstrated. The adaptive array performance is dominated by this coefficient and can be improved by properly choosing the first three factors. Several examples on the selection of element placement in adaptive arrays are presented.
TL;DR: In this paper, a unified quantitative treatment of the attenuation and backscatter characteristics of radars operating in the range 1 to 10 GHz with particular emphasis at L - and S -band was presented.
Abstract: Meager information has hitherto been reported as to the influence of dust storms on radars operating in desert regions. This work represents an attempt to bring together the results of a body of diverse investigations and present a unified quantitative treatment of the attenuation and backscatter characteristics of radars operating in the range 1 to 10 GHz with particular emphasis at L - and S -band. The results demonstrate that for extreme mass loading values (40-60 gm/ m-3) the two-way attenuation may be as high as 44 dB over a one-way range of 20 km. Such a mass loading uniformly spread over this range is, however, considered very unlikely. Assuming typical S - and L -band radar parameters and the above extreme dust concentrations filling the pulse volumes at a range of 100 km, equivalent point target cross sections of approximately 2 and 1 m2result at the respective frequencies.
TL;DR: In this paper, the decrease in aperture efficiency caused by small aberrations in a reflector antenna is determined, and conditions that optimize performance are given for the design of multibeam antennas in ground stations and satellites.
Abstract: The decrease in aperture efficiency caused by small aberrations in a reflector antenna is determined The important case of a Cassegrainian (or Gregorian) antenna with a feed placed in the vicinity of the focal point is treated in detail For this case the various aberration components due to astigmatism, coma, etc, are derived explicitly, their effect on aperture efficiency is shown, and the conditions that optimize performance are given The results are useful for the design of multibeam antennas in ground stations and satellites
TL;DR: In this article, the integral arising in the Wiener-hopf solution for wide microstrip antennas were approximated in closed form for the case of an electrically thin substrate.
Abstract: Integrals arising in the Wiener-Hopf solution for wide microstrip antennas are approximated in closed form for the case of an electrically thin substrate. The resulting expressions are used to obtain simple, closed-form expressions for resonant frequency and unloaded radiation Q for rectangular microstrip patch antennas which are valid when commonly used quasi-static formulas no longer hold. Numerical comparisons show significant shifts in resonant frequencies as compared with existing theories.