Showing papers in "IEEE Transactions on Antennas and Propagation in 1985"
TL;DR: The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles, and the bandwidth limitation of the method is discussed.
Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.
594 citations
TL;DR: In this article, a good general agreement is obtained for curves of beamwidth versus length, normalized to wavelength, when one compares the data with that for traveling-wave antennas published by Zucker.
Abstract: Endfire tapered slot antennas are suitable for many integrated circuit applications, imaging and phased arrays. We report on an investigation of single elements of such antennas, including slots which are exponentially tapered (Vivaldi), linearly tapered (LTSA) and constant width (CWSA). For antennas of all types, a good general agreement is obtained for curves of beamwidth versus length, normalized to wavelength, when one compares the data with that for traveling-wave antennas published by Zucker. An important condition for this agreement is that the effective dielectric thickness, defined in the text, is in a certain optimum range. This condition is qualitatively explained in terms of the theory for traveling-wave antennas.
453 citations
TL;DR: In this paper, the authors proposed a planar antenna which can radiate circularly polarized pencil beams in the x-band for the application of receiving direct broadcast from a satellite (DBS).
Abstract: The analysis and design of novel planar antennas which can radiate circularly polarized pencil beams in x -band are presented for the application of receiving direct broadcast from a satellite (DBS). This antenna belongs to a class of slotted waveguide antennas and high efficiency is expected in principle. A circular two-dimensional aperture is located on the top plate of a twofold radial waveguide and is excited by a radially inward traveling transverse electromagnetic (TEM) mode in the upper waveguide. Slots are arrayed on the aperture spirally in such a way that they can couple with the radial currents flowing over the aperture plate to produce a circularly polarized broadside beam. Promising performances of the antenna are predicted theoretically. Experiments are performed with respect to basic characteristics of the antenna and they show the validity of the design and analysis.
274 citations
TL;DR: In this article, two novel configurations for increasing the impedance bandwidth of the microstrip patch antennas are described, one of which uses two additional resonators which are gap-coupled to the nonradiating edges of a rectangular patch, whereas in the second case, four extra resonators are gap coupled to the four edges of the rectangular patch.
Abstract: Two novel configurations for increasing the impedance bandwidth of the microstrip patch antennas are described. One of these configurations uses two additional resonators which are gap-coupled to the nonradiating edges of a rectangular patch, whereas in the second case, four additional resonators are gap-coupled to the four edges of a rectangular patch. Green's function approach and segmentation method are used for analysis. The experimental results are in reasonable agreement with analysis and impedance bandwidths of 480 MHz and 815 MHz are obtained for the three resonators and five resonators configurations, respectively (in S -band with substrate \epsilon_{r} = 2.55 and thickness = 0.318 cm).
224 citations
TL;DR: In this paper, the moment method in the Fourier transform domain was used to calculate the impedance, resonant length, and radiation pattern for the isolated antennas and the reflection coefficient for infinite phased arrays.
Abstract: The printed dipole or slot antenna on a semi-infinite substrate and infinite phased arrays of these elements are investigated. The solution is based on the moment method in the Fourier transform domain. The generalized impedance or admittance matrix can be expressed in rapidly converging infinite-integral or infinite-summation forms, allowing the accurate determination of the current distributions. Using the present formulation, the input impedance, resonant length, and radiation pattern for the isolated antennas, and the reflection coefficient for infinite phased arrays, are calculated.
195 citations
TL;DR: A numerical method and experimental technique for microwave imaging of inhomogenous bodies is presented in this article, which is based on the interpretation of the diffraction phenomena and leads to tomographic reconstruction of the body under investigation.
Abstract: A numerical method and experimental technique for microwave imaging of inhomogenous bodies is presented. This method is based on the interpretation of the diffraction phenomena and leads to tomographic reconstruction of the body under investigation. Various numerical examples are given on spatial impulse response, recognition of dielectric rods, inhomogeneous bodies, and simulated human arm. Different experimental results on dielectric rods and isolated animal organs are also given.
192 citations
TL;DR: In this article, an aspect independent radar target discrimination scheme based on the natural frequencies of the target is considered, and an extinction-pulse waveform upon excitation of a particular conducting target results in the elimination of specified natural modal content of the scattered field.
Abstract: An aspect independent radar target discrimination scheme based on the natural frequencies of the target is considered. An extinction-pulse waveform upon excitation of a particular conducting target results in the elimination of specified natural modal content of the scattered field. Excitation of a dissimilar target produces a noticeably different late-time response. Construction of appropriate extinction-pulse waveforms is discussed, as well as the effects of random noise on their application to thin cylinder targets. Also presented is experimental verification of this discrimination concept using simplified aircraft models.
152 citations
TL;DR: In this article, a model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally, and a comparison of theoretical predictions and experimental data were made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance.
Abstract: A previously derived theory is applied to a microstrip antenna with a reactive load to produce a dual-band radiator. A model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally. Comparisons of theoretical predictions and experimental data are made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance of the stub.
144 citations
TL;DR: In this article, a uniform high-frequency solution is presented for the diffraction by a wedge with impedance faces illuminated by a plane wave perpendicularly incident on its edge, and both the transverse electric (TE) and transverse magnetic (TM) cases are considered.
Abstract: A uniform high-frequency solution is presented for the diffraction by a wedge with impedance faces illuminated by a plane wave perpendicularly incident on its edge. Arbitrary uniform isotropic impedance boundary conditions may be imposed on the faces of the wedge, and both the transverse electric (TE) and transverse magnetic (TM) cases are considered. This solution is formulated in terms of a diffraction coefficient which has the same structure as that of the uniform geometrical theory of diffraction (UTD) for a perfectly conducting wedge. Its extension to the present case is achieved by introducing suitable multiplying factors, which have been derived from an asymptotic evaluation of the exact solution given by Maliuzhinets. When the field point is located on the surface near the edge, a more accurate asymptotic evaluation is employed to obtain a high-frequency expression for the diffracted field, which is suitable for several specific applications. The formulation described in this paper may provide a useful, rigorous basis to search for a more numerically efficient but yet accurate approximation.
142 citations
TL;DR: The first approximation to the aperture efficiency of a paraboloidal reflector antenna is called the feed efficiency as mentioned in this paper, which is derived by factorizing the antenna's feed efficiency into subefficiencies which account for losses due to spillover, cross polarization, nonuniform aperture illumination, and phase errors.
Abstract: The first approximation to the aperture efficiency of a paraboloidal reflector antenna is called the feed efficiency. The factorization of the feed efficiency into subefficiencies which account for losses due to spillover, cross polarization, nonuniform aperture illumination, and phase errors is considered. The relations between the radiation patterns of circularly and linearly polarized feeds are also derived.
139 citations
TL;DR: In this paper, an approach to the analysis of microstrip antennas on cylindrical bodies is presented, where the printed radiator is replaced by as assumed surface current distribution, and the fields are solved taking into account the presence of the dielectric layer and the metallic cylinder.
Abstract: An approach to the analysis of microstrip antennas on cylindrical bodies is presented. The printed radiator is replaced by as assumed surface current distribution, and the fields are solved taking into account the presence of the dielectric layer and the metallic cylinder. Calculation takes place in the Fourier domain. The far field, calculated asymptotically from this solution, is used to get the radiation patterns of the wraparound antenna for any dielectric and the half-wavelength patch for \epsilon_{r} = 1 .
TL;DR: In this article, three new configurations for increasing the impedance bandwidth of the microstrip patch antennas are described, where additional resonators are directly coupled through short sections of microstrip line to the radiating edges, nonradiating edges, and all the four edges of the rectangular patch antennas, respectively.
Abstract: Three new configurations for increasing the impedance bandwidth of the microstrip patch antennas are described. In these configurations, additional resonators are directly coupled through short sections of microstrip line to the radiating edges, nonradiating edges, and all the four edges of the rectangular patch antennas, respectively. Green's function approach and segmentation method are used for the analysis. The experimental results are in reasonable agreement with the analysis and impedance bandwidths of 548 MHz, 605 MHz, and 810 MHz are obtained for these three configurations, respectively in S -band (substrate thickness = 0.318 cm and \epsilon_{r} = 2.55 ). The variation in the radiation pattern over this impedance bandwidth is discussed.
TL;DR: In this paper, the dc conductivity and complex dielectric constant at frequencies of 7.50, 9, 11, 30, and 40 GHz of 16 samples of sea water brine in equilibrium with sea ice with freezing temperatures ranging from - 2.8\deg C to -25.0
Abstract: The dc conductivity and complex dielectric constant at frequencies of 7.50, 9, 11, 30, and 40 GHz of 16 samples of sea water brine in equilibrium with sea ice with freezing temperatures ranging from - 2.8\deg C to -25.0\deg C have been measured. The data is analyzed to yield parameters occurring in a Debye relaxation equation so that the dielectric constant of brine may be calculated throughout the microwave region of the electromagnetic spectrum.
TL;DR: In this article, a class of finite step iterative methods for the solution of linear operator equations is presented, and the basic principles of the method of conjugate directions are developed.
Abstract: A class of finite step iterative methods for the solution of linear operator equations is presented. Specifically, the basic principles of the method of conjugate directions are developed. Gaussian elimination and the method of conjugate gradients are then presented as two special cases. With an arbitrary initial guess, the method of conjugate gradient always converges to the solution in at most N iterations, where N is the number of independent eigenvalues for the operator in the finite dimensional space in which the problem is being solved. The conjugate gradient method requires much less storage ( \sim 5N ) than the conventional matrix methods ( \sim N^{2} ) in the solution of problems of higher complexity. Also, after each iteration the quality of the solution is known in the conjugate gradient method. The conjugate gradient method is also superior to the spectral iterative method as the latter does not always converge and it doubles the complexity of a given problem, unnecessarily. Four versions of the conjugate gradient method are presented in detail, and numerical results for a thin wire scatterer are given to illustrate various properties of each version.
TL;DR: In this article, the effects of focused aperture amplitude tapering, both direct and inverse, on axial forelobes and aft lobes are investigated, where the peak axial power density occurs between the aperture and the phase (geometric) focus, due to the 1/R^{2} factor.
Abstract: The effects of focused aperture amplitude tapering, both direct and inverse, on axial forelobes and aftlobes are investigated. Taylor tapers give low sidelobes but high forelobes and aftlobes, plus a modest gain degradation. Inverse tapers give low forelobes and aftlobes but high sidelobes and large gain degradation. Uniform excitation gives comparable axial and transverse subsidiary lobes, and is probably the best choice. Focal shift, where the peak axial power density occurs between the aperture and the phase (geometric) focus, due to the 1/R^{2} factor, is accurately calculated for a uniform square aperture. Since peak axial power density available from a focused aperture depends only on aperture size in wavelengths and on distance, these focal shift results allow system trade-offs to be made.
TL;DR: The purpose of this paper is to investigate the effects of motions on the SAR multilook images of moving targets and derive expressions for the impulse response function from a moving point target in terms of the look number and the nature of the motion.
Abstract: In the multilook processing of synthetic aperture radar (SAR) data, subapertures are synthesized at different center times so that a time-lapse exists between looks. This does not affect the imaging of stationary targets but if targets are in motion, the information content about the targets differs from look to look. The purpose of this paper is to investigate the effects of motions on the SAR multilook images of moving targets. Expressions are derived for the impulse response function from a moving point target in terms of the look number and the nature of the motion. Discussions are given only on the effects inherent to multilook processing.
TL;DR: In this article, it was shown that Michaeli's results relate to Mitzner's for arbitrary directions in identically the way Keller's relate to Ufimtsev's for directions on the Keller cone.
Abstract: Michaeli recently derived a set of equivalent edge currents for scattering directions not on the Keller cone. Some years ago, Mitzner developed his incremental length diffraction coefficient (ILDC) for the same purpose. It is shown that Michaeli's results relate to Mitzner's for arbitrary directions in identically the way Keller's relate to Ufimtsev's for directions on the Keller cone.
TL;DR: In this article, the authors determined the input impedance and bandwidth of an annular ring microstrip antenna by modeling the antenna as a section of radial line loaded with wall admittances and taking the effect of mutual coupling between the radiating apertures into account.
Abstract: Input impedance and bandwidth of an annular ring microstrip antenna have been determined by modeling the antenna as a section of radial line loaded with wall admittances. The effect of mutual coupling between the radiating apertures has been taken into account. The theoretically calculated values of input impedance for TM 12 -mode are compared with measurements. The agreement is good. Higher order modes have been found to be present in the vicinity of TM 12 -mode. The reactance due to these modes can be utilized to increase the voltage standing-wave ratio (VSWR) bandwidth of the antenna.
TL;DR: In this paper, an approach to the analysis of microstrip antennas which is applicable also to relatively thick substrates using the relevant Green's function is presented and closed form expressions for various antenna characteristics which explicitly take into account the presence of the dielectric material are obtained in terms of the electric surface current density.
Abstract: An approach to the analysis of microstrip antennas which is applicable also to relatively thick substrates using the relevant Green's function is presented. The Green's function is derived and closed form expressions for various antenna characteristics which explicitly take into account the presence of the dielectric material are obtained in terms of the electric surface current density. For rectangular microstrip elements near resonance the current distribution is approximated using lossless transmission line analysis, thus enabling the complete evaluation of the characteristics of the element near resonance. The results obtained in this approach for the radiation resistance, surface wave resistance, radiation pattern, directivity, and bandwidth are presented in a detailed set of graphs for a representative set of parameters.
TL;DR: In this article, integral equation formulations for characterizing the electromagnetic (EM) scattering interaction for nonmetallic surfaces are presented for general geometry, and the current expansion functions, which are chosen, result in a symmetric system of equations.
Abstract: Integral equation formulations are presented for characterizing the electromagnetic (EM) scattering interaction for nonmetallic surfaced bodies. Three different boundary conditions are considered for the surfaces: namely, the impedance (Leontovich), the resistive sheet, and its dual, the magnetically conducting sheet boundary. The integral equation formulations presented for a general geometry are specialized for bodies of revolution and solved with the method of moments (MM). The current expansion functions, which are chosen, result in a symmetric system of equations. This system is expressed in terms of two Galerkin matrix operators that have special properties. The solutions of the integral equation for the impedance boundary at internal resonances of the associated perfectly conducting scatterer are examined. The results are compared with the Mie solution for impedance-coated spheres and with the MM solutions of the electric, magnetic, and combined field formulations for impedance-coated bodies.
TL;DR: In this paper, a combination resistive and conductive sheet is defined and its properties described to simulate a thin layer of material whose permittivity and permeability both differ from the values for the surrounding medium.
Abstract: To simulate a thin layer of material whose permittivity and permeability both differ from the values for the surrounding medium, a combination resistive and conductive sheet is defined and its properties described.
TL;DR: In this article, the problem of scattering from a resistive strip grating is formulated in the spectral domain, and numerical calculations of the reflection coefficient are presented for perfectly conducting strips and strips with resistivities up to 750 ε/square.
Abstract: The problem of scattering from a resistive strip grating is formulated in the spectral domain. Results of numerical calculations of the reflection coefficient are presented for perfectly conducting strips and strips with resistivities up to 750\Omega /square.
TL;DR: In this article, an analysis for determining the current induced by a known excitation on a conducting cylinder located near the planar interface between two semi-infinite, homogeneous half-spaces of different electromagnetic properties is described.
Abstract: An analysis is described for determining the current induced by a known excitation on a conducting cylinder located near the planar interface between two semi-infinite, homogeneous half-spaces of different electromagnetic properties. The perfectly conducting cylinder of general cross section is of infinite extent and the excitation is transverse magnetic to the cylinder axis. An integral equations for the induced current is derived and a numerical method for solving it is developed. The kernel of the integral equation contains a term corresponding to the usual open-space Green's function plus a term proportional to a Sommerfeld-type integral in two dimensions. Various forms of the Sommerfeld-type integral are given and the choices of form amenable to efficient evaluation are discussed. For a flat strip, a circular cylinder, and a rectangular cylinder, data are presented and discussed for selected parameters. Data are presented for cylinders above and below the interface as well as for a cylinder resting on the interface.
TL;DR: In this article, a probe-corrected spherical transmission formula was proposed for spherical near-field measurements, which retains the form, applicability, and simplicity of the nonprobecorrected equations, and is consistent with the previous transmission formula derived from the rotational and translational addition theorems for spherical waves.
Abstract: The general receiving antenna is represented as a linear differential operator converting the incident field and its spatial derivatives at a single point in space to an output voltage. The differential operator is specified explicitly in terms of the multipole coefficients of the antenna's complex receiving pattern. When the linear operator representation is applied to the special probes used in spherical near-field measurements, a probe-corrected spherical transmission formula is revealed that retains the form, applicability, and simplicity of the nonprobe-corrected equations. The new spherical transmission formula is shown to be consistent with the previous transmission formula derived from the rotational and translational addition theorems for spherical waves.
TL;DR: In this article, the Misell algorithm has been used successfully to retrieve the aperture phase distribution from two numerically simulated power polar diagrams, one in focus and the second defocused, using no auxilliary reference antenna.
Abstract: Methods of phase retrieval from simulated intensity information have been tested for use in the radio holography of reflector antennas In numerical simulations the Misell algorithm has been used successfully to retrieve the aperture phase distribution from two numerically simulated power polar diagrams, one in focus and the second defocused The technique uses no auxilliary reference antenna However, it does need a high signal to noise ratio, typically 50 dB if a 60 \times 60 array is to be measured to a precision such that the gain is within 1 percent of ideal It should be most useful where no direct phase measurements are possible and ground-based or satellite transmitters can be used as sources The use of astronomical maser sources (22 GHz) can give information on large scale deformations
TL;DR: In this paper, a general computer program for low frequency scattering of electromagnetic fields by solid/hollow dielectric or conducting cylinders using the boundary element method (BEM) was developed for both transverse electric and magnetic cases.
Abstract: The computation of low frequency scattering of electromagnetic fields by solid/hollow dielectric or conducting cylinders using the boundary element method (BEM) is considered. A general computer program has been developed for both transverse electric and magnetic cases. Numerical examples are given for conducting circular cylinders, and solid and hollow dielectric cylinders. The computational accuracy is checked by comparing the results with the analytic solution or computing an error defined from the optical theorem. In addition some problems at an interior resonance of the scatterer are discussed. The method can be directly applied to more complicated geometries.
TL;DR: The singularity expansion method (SEM) as mentioned in this paper represents transient scattering by superposition of damped oscillatory fields corresponding to the complex resonant frequencies of the scatterer.
Abstract: The singularity expansion method (SEM) represents transient scattering by superposition of damped oscillatory fields corresponding to the complex resonant frequencies of the scatterer. The series of these global wave fields, which encompass the scattering object as a whole, is slowly convergent at early observation times and even deficient at very early times when portions of the object are as yet unexcited. Thus, the resonance series representation must generally be augmented by an entire function in the complex frequency domain. The choice of the entire function is relatively arbitrary but affects the excitation coefficients, called coupling coefficients, of individual resonances and also the "turn-on" and "switch-on" times of the SEM series. Moreover, it contains essential (intrinsic) and nonessential (removable) portions which have been subjected to various interpretations. By formulating the transient problem in terms of traveling (progressing) incident, reflected and diffracted wavefronts, these constructs in the SEM can be interpreted in a precise and physical manner. Furthermore, the analysis clarifies the evolution of resonances as collective summations of multiple wavefront fields which are caused by successive reflections or diffractions at the surfaces and scattering centers comprising the object. By combining wavefronts and resonances self-consistently, one may construct a hybrid field that avoids the difficulties at early times in the SEM formulation. The systematic exploration of the interplay between wavefronts and resonances is facilitated through use of a flow diagram, as introduced in system theory. These concepts are developed in broad generality and are illustrated for two-dimensional scattering by various special configurations.
TL;DR: In this paper, a closed-form solution for the cluster excitation to achieve the optimum directivity was presented for an offset 108 λ parabolic reflector antenna scanning 10 beamwidths, and the optimum-directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element.
Abstract: The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of a single feed is used to control a beam. A closed-form solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 \lambda parabolic reflector scanning 10 beamwidths, the optimum-directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimum-directivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 \lambda , it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d , the optimum design may exhibit the supergain phenomenon, namely, extremely high directivities achieved by an oscillatory cluster excitation.
TL;DR: In this article, the radiation from a dipole in the presence of a grounded general gyromagnetic-electric (gyrotropic) layer is investigated, and the use of matrix methods in conjunction with Fourier transformation techniques greatly facilitates the formulation of the boundary-value problem, reducing the algebraic complexity to a minimum, and provides a closed-form representation of the electromagnetic field over the anisotropic region.
Abstract: The radiation from a dipole in the presence of a grounded general gyromagnetic-electric (gyrotropic) layer is investigated. The use of matrix methods in conjunction with Fourier transformation techniques greatly facilitates the formulation of the boundary-value problem, reducing the algebraic complexity to a minimum, and provides a closed-form representation of the electromagnetic field over the anisotropic region. Numerical results in plots, related to the radiation pattern of the structure, are also included for various cases.
TL;DR: In this article, the dielectric wedge, the metallic 90-deg corner on a polygonal plane, and the adjacent 90-degree metallic corners are discussed, and numerical data are given for n, and plots of lines of force of \bar{e} (or \ bar{h} ) are shown.
Abstract: The wedges discussed are the dielectric wedge, the metallic 90\deg corner on a dielectric plane, and the adjacent 90\deg metallic and dielectric corners. The field components perpendicular to the edge may become infinite according to a law ( 1/r^{n} ). Numerical data are given for n , and plots of lines of force of \bar{e} (or \bar{h} ) are shown.