Showing papers in "IEEE Transactions on Antennas and Propagation in 1979"
TL;DR: In this article, a simple theory based on the cavity model was developed to analyze microstrip antennas, and the theoretically predicted radiation patterns and impedance loci closely agree with those measured for many antennas of various shapes and dimensions investigated thus far.
Abstract: A simple theory based on the cavity model is developed to analyze microstrip antennas. Formulas for numerous canonical shapes are given. In general the theoretically predicted radiation patterns and impedance loci closely agree with those measured for many antennas of various shapes and dimensions investigated thus far. In fact, this theory enables the computation of both patterns and impedance loci with little effort. The input admittance locus generally follows a circle of nearly constant conductance, but its center is shifted to the inductive region in the Smith chart plot. Peculiar properties for the case with degenerate or slightly degenerate eigenvalues are discussed. An accurate formula for determining the resonant frequency of a rectangular microstrip antenna is also given.
882 citations
TL;DR: In this article, the formation of wave-like patterns in SAR images of the ocean surface caused by orbital motions is investigated, and the degradation in azimuthal resolution due to these motions is calculated by applying a least square fit to the phase history.
Abstract: The formation of wave-like patterns in synthetic aperture radar (SAR) images of the ocean surface caused by orbital motions is investigated. Furthermore, the degradation in azimuthal resolution due to these motions is calculated by applying a least square fit to the phase history. Formulas are given which describe the variation of intensity in azimuthal direction in the image plane as well as the degradation in azimuthal resolution as a function of ocean wave amplitude, wave frequency, direction of wave propagation, and radar wavelength, incidence angle, and integration time.
272 citations
TL;DR: In this article, a dichroic subreflector for a dual-frequency reflector antenna is described, which is achieved by a surface of crossed dipoles printed on a dielectric sheet.
Abstract: The design of a dichroic subreflector for a dual-frequency reflector antenna is described. This antenna consists of a Ku -band Cassegrain feed requiring the subreflector surface to be highly reflective at 13-15 GHz and a primary focus S -band feed requiring the subreflector to be transparent at 2.0-2.3 GHz. Such a performance is achieved by a surface of crossed dipoles printed on a dielectric sheet. The influence of parameters, dipole length, width and spacing, and the dielectric constant and thickness of the sheet on the reflection and transmission coefficients is experimentally evaluated. An analysis based upon the Floquent mode theory is shown to correctly predict the experimental results. The construction of a hyperbolic subreflector using the selected surface parameters is briefly described. As compared to a solid subreflector of identical shape, this dichroic subreflector produced a negligible loss (less than 0.1 dB) over a 13-15 GHz band. At the S band the loss was less than 0.2 dB over narrow selected bands and the axial ratio deterioration was also no more than 0.2 dB.
188 citations
TL;DR: In this paper, a cylindrical cavity with magnetic walls is modeled as a circular microstrip antenna element, which can be resonant in the transverse magnetic (TM) modes, assuming a magnetic line current flowing along the perimeter of the disk.
Abstract: The circular microstrip antenna element is formed by a radiating disk closely spaced above a ground plane. It is modeled as a cylindrical cavity with magnetic walls which can be resonant in the transverse magnetic (TM) modes. The far fields and the radiation conductances for different mode structures have been calculated assuming a magnetic line current flowing along the perimeter of the disk. The directivity of a disk antenna excited in the dominant mode is between 4.8 dB and 9.9 dB, depending on the size. Losses, due to imperfect supporting dielectrics and to the finite conductivity of the conductors, have been derived by means of a perturbation technique. Graphs are given for design purposes showing the input impedance, the Q factor, and the radiation efficiency at resonance for different modes and thicknesses. The air-filled microstrip antenna has the highest efficiency and the broadest bandwidth at a given resonant frequency.
188 citations
TL;DR: In this article, an infinite array of arbitrarily oriented identical elements with arbitrary identical currents is considered, and the mutual impedance between the array elements and an exterior arbitrarily oriented element is derived, particularly useful when the array is located adjacent to a dielectric interface.
Abstract: An infinite array of arbitrarily oriented identical elements with arbitrary identical currents is considered. The field from this array is expanded into plane inhomogeneous waves, and the mutual impedance between the array elements and an exterior arbitrarily oriented element is derived. The formulation is particularly useful when the array is located adjacent to a dielectric interface. Numerical examples are given and the relationship to earlier formulations pointed out. It is further shown that the impedance of a single element can be obtained as the average of the scan impedance taken over the entire hemisphere (called the array scanning method (ASM)). This technique has a clear physical interpretation which greatly facilitates its uses, which include the moment method solutions of wire antennas as applied to the Sommerfeld integral. Numerical evaluation is straightforward when the dipole is in the lossy half-space, and the utility of the method is demonstrated by the presentation of results for the input impedance of dipoles in a variety of half-space environments. Solution is by Galerkin's method with a piecewise sinusoidal expansion for the current. Computer time is proportional to d^{-1} , where d is the distance of the dipole to the interface. For conducting media and low frequencies an approximation is made to reduce computation time. The moment method solution of a dipole buried at a depth as small as 1/150000 wavelength in the earth is presented.
170 citations
TL;DR: In this paper, a combined-source solution for electromagnetic radiation and scattering from a perfectly conducting body is developed for a three-dimensional closed surface S, which is then applied to a surface of revolution.
Abstract: A combined-source solution is developed for electromagnetic radiation and scattering from a perfectly conducting body. In this solution a combination of electric and magnetic currents, called the combined source, is placed on the surface S of the conducting body. The combined-source operator equation is obtained from the E -field boundary-value equation. It is shown that the solution to this operator equation is unique at all frequencies. The combined-field operator equation also has a unique solution, but it is not directly applicable to the aperture radiation problem. The H -field and E -field operator equations fail to give unique solutions at frequencies corresponding to the resonant frequencies of a cavity formed by a hollow conductor of the same shape. The combined-source operator equation is solved by the method of moments. The solution, valid for a three-dimensional closed surface S , is then applied to a surface of revolution. Examples of numerical computations are given for a sphere, a cone-sphere, and a finite circular cylinder.
164 citations
TL;DR: In this paper, the fundamental problem of printed antennas is addressed, and the Green's function to the problem is obtained in dyadic form by solving the problem of a Hertzian dipole printed on a grounded substrate.
Abstract: The fundamental problem of printed antennas is addressed. The printed or microstrip dipole is considered, and its radiation characteristics are investigated. The Green's function to the problem is obtained in dyadic form by solving the problem of a Hertzian dipole printed on a grounded substrate. Input impedance computations are presented, and the numerical solution for the Sommerfeld integrals is discussed.
160 citations
TL;DR: In this article, a variational finite-element algorithm was proposed to solve the problem of time-harmonic electromagnetic scattering by axisymmetric penetrable bodies having arbitrary cross-sectional profiles and continuous inhomogeneous consistency.
Abstract: This investigation is concerned with the numerical solution of time-harmonic electromagnetic scattering by axisymmetric penetrable bodies having arbitrary cross-sectional profiles and even continuously inhomogeneous consistency. The initiation of this effort involved the discovery and development of the coupled azimuthal potential (CAP) formulation, which is valid in generally lossy isotropic inhomogeneous rotationally symmetric media. Electromagnetic fields in such regions can be represented, using the CAP formulation, in terms of two continuous potentials which satisfy a self-adjoint system of partial differential equations or, equivalently, a variational criterion. Using an optimized variational finite-element algorithm in conjunction with a triregional unimoment method, a versatile computer program is described that provides scattering solutions for each of multiple incident fields impinging upon an arbitrarily shaped inhomogeneous penetrable body of revolution. An extensive evaluation of the accuracy and convergence of the algorithm is presented, which includes comparison of scattering computations and experimental measurements at X -band for several solid and hollow plexiglas bodies of revolution with maximum interior dimensions of over 4 wavelengths.
155 citations
TL;DR: In this article, the efficiency of a small antenna can be substantially increased by properly locating it on its support structure, and the characteristic modes are used to determine the optimum location and frequency.
Abstract: It is shown that the efficiency of a small antenna can be substantially increased by properly locating it on its support structure Characteristic modes are used to determine the optimum location and frequency
115 citations
TL;DR: In this article, a theory for the radar imaging of ocean waves is presented under the assumptions that a swell propagates through an ensemble of Bragg scatterers and that the integration time of the synthetic aperture radar (SAR) is small compared to the angular velocity of the swell.
Abstract: A theory for the radar imaging of ocean waves is presented under the assumptions that a swell propagates through an ensemble of Bragg scatterers and that the integration time of the synthetic aperture radar (SAR) is small compared to the angular velocity of the swell. Results are prsented which show image development and distortions caused by the radial velocities and accelerations of the swell. Neglecting small wave bunching and tilts due to the longer underlying waves, and considering only one-dimensional geometries, the mechanism of wave motions are considered and their efforts on the production of the usual intensity Pattern representing the wave image are studied. The analysis shows that in certain situations a processed image can appear which has twice the spatial period of the actual long wave on the ocean, which can confuse the interpretation of ocean wave analysis.
114 citations
TL;DR: In this paper, an extended theory on rectangular microstrip resonator antennas is presented using the cavity model, where radiation from all four edges of the open cavity is taken into account as well as dielectric and ohmic losses.
Abstract: An extended theory on rectangular microstrip resonator antennas is presented using the cavity model. Radiation from all four edges of the open cavity is taken into account as well as dielectric and ohmic losses. For a rectangular microstrip antenna excited in its lowest resonance mode, losses, input conductance, and bandwidth are calculated and plotted versus frequency for some different parameters, showing that bandwidths of up to 15 percent (for a voltage standing-wave ratio (VSWR) of less than two) are possible to achieve in the X band.
TL;DR: General coordinate transformations which are commonly encountered in many antenna applications are presented and attempts are made to use unified notations to assist the reader in a straightforward application of the transformations.
Abstract: General coordinate transformations which are commonly encountered in many antenna applications are presented. Neither the feed coordinates nor the far-field pattern coordinates in general coincide with the antenna coordinates. Transformations discussed allow one to relate the spherical and Cartesian components of one system to the spherical and Cartesian compoents of the other system. In particular, attempts are made to use unified notations to assist the reader in a straightforward application of the transformations.
TL;DR: In this article, the surface field and far field of a resistive strip for a variety of strip widths w and uniform resistances R were obtained using the moment method applied to an appropriate integral equation.
Abstract: Strips made of a resistive sheet material have lower backscattering cross sections than the corresponding perfectly conducting strips, and this is true in particular when the illumination is edge-on with the electric vector parallel to the edge. Attention is focused on this case. Using the moment method applied to an appropriate integral equation, data are obtained for the surface field and backscattered far field of a resistive strip for a variety of strip widths w and uniform resistances R . The front- and rear-edge contributions to the far field are then extracted. It is shown that for strips whose width is greater than about a half-wavelength the former is the same as for a half-plane having the same resistance, whereas the latter is proportional to the square of the current at that point on the half-plane corresponding to the rear edge of the strip. The implications of these results on the selection of a strip resistance for low backscattering are discussed.
TL;DR: In this article, the authors show that the performance of current passive microwave radiometers is meteorology-profile dependent due to incorrect frequency combinations and saturation of brightness temperatures, and that by properly selecting an optimum frequency pair and removing the saturation effect, the dependency can be alleviated and can be further adjusted by surface measurements alone.
Abstract: Radio-astronomical observations require accurate calibration of tropospheric path length. Such calibration can be achieved by microwave radiometers operating near the 22-GHz water vapor line. However, the performances of current passive microwave radiometers are meteorology-profile dependent. This is shown due mainly to incorrect frequency combinations and to saturation of brightness temperatures. By properly selecting an optimum frequency pair and removing the saturation effect, the dependency is alleviated and can be further adjusted by surface measurements alone. Hence, a universal calibration equation is applicable to all environmental conditions. Optimum frequency pairs are systematically searched. Simulation analysis indicates that calibration for the tropospheric water-vapor path-length error is better than 0.3 cm at zenith and better than 2 cm for an elevation angle as low as 10\deg .
TL;DR: In this paper, a simple and efficient numerical procedure is presented for determining the static charge distribution on arbitrary-shaped surfaces, where surfaces are modeled by planar triangular subdomains in which the charge density is assumed to be constant.
Abstract: A simple and efficient numerical procedure is presented for determining the static charge distribution on arbitrary-shaped surfaces. Surfaces are modeled by planar triangular subdomains in which the charge density is assumed to be constant. The method of moments is employed to calculate the charge distribution on the surface.
TL;DR: In this paper, the reflection coefficient versus frequency of symmetrical crossed-dipole arrays exhibits two distinct resonances, which occur when the dipole elements are on the order of a half-wavelength long.
Abstract: An analysis is presented for calculating the scattering from periodic arrays of symmetrical crossed dipoles. It is shown that in general the reflection coefficient versus frequency of symmetrical crossed-dipole arrays exhibits two distinct resonances, which occur when the dipole elements are on the order of a half-wavelength long. The analysis reveals also the presence of an antiresonance, which occurs at a frequency between the two resonances. At the antiresonant frequency the array reflection coefficient is zero. Thus, within a relatively narrow frequency band, the array reflection characteristics traverse the extremes of complete reflection followed by no reflection, and finally by complete reflection again. The anomalous reflection versus frequency behavior in such arrays is shown to be directly attributable to two distinct resonances excited in the crossed elements. For an isolated crossed dipole, it is shown that the total induced current can be approximately represented by two uncoupled current components. The current components induced on the same elements in an array, however, are coupled to one another through interaction with neighboring elements. The coupling results in complete cancellation of the total bistatic array scattering, at a frequency which lies between the two component current resonant frequencies.
TL;DR: In this article, an adaptive antenna array can achieve an angular resolution of uncorrelated interference sources substantially greater than the aperture of diffraction limit by using adaptive techniques, where the antenna beam is scanned over the interference source locations and for each scan condition the adaptive processor is allowed to reach its steady state.
Abstract: By using adaptive techniques an antenna array can achieve an angular resolution of uncorrelated interference sources substantially greater than the aperture of diffraction limit. The antenna beam is scanned over the interference source locations, and for each scan condition the adaptive processor is allowed to reach its steady state. It is shown that for realistic ratios of interference strengths to system thermal noise, resolutions in excess of 0.25 times the Rayleigh limit can be achieved.
TL;DR: In this article, a series approach for the rapid computation of the vector secondary pattern of offset paraboloid reflectors wherein the feed is displaced is presented, which has been demonstrated to provide an efficient means for evaluating the radiation integral of symmetric parabolic reflectors without compromising the ease or speed of computation.
Abstract: A series approach for the rapid computation of the vector secondary pattern of offset paraboloid reflectors wherein the feed is displaced is presented. We show that the Jacobi polynomial series method, which has been demonstrated to provide an efficient means for evaluating the radiation integral of symmetric paraboloid reflectors, can be extended to the case of an offset paraboloid without compromising the ease or speed of computation. The analysis leading to the series formula is also useful for deriving an analytic expression for the optimum scan plane for the displacement of the feed. Representative numerical results illustrating the application of the method and the properties of the offset paraboloid are presented.
TL;DR: In this paper, the concept of Stokes vectors and Stokes target operators is used to obtain optimum antenna polarizations for target discrimination in the presence of background clutter, and the analysis involves a constrained maximization of the ratio of two bilinear forms, representing the signal-to-interference power ratio.
Abstract: The concept of Stokes vectors and Stokes target operators is used to obtain optimum antenna polarizations for target discrimination in the presence of background clutter. The analysis involves a constrained maximization of the ratio of two bilinear forms, representing the signal-to-interference power ratio.
TL;DR: In this paper, a two-port network and geometrical interpretation of equations involved in antenna scattering is used to determine antenna characteristics in properly designed scattering measurements, which can be used for measurement procedures for gain and radiation pattern, based on simple considerations of the receiving, transmitting, and scattering properties of antennas.
Abstract: Using a two-port network and geometrical interpretation of equations involved in antenna scattering, it can be derived that antenna characteristics may be determined in properly designed scattering measurements. As an alternative to this approach it is shown that measurement procedures for gain and radiation pattern can be developed from simple considerations of the receiving, transmitting, and scattering properties of antennas. The main advantages of the technique are that no gain standard is required and a disturbing feedline to the antenna can be avoided. In addition to this the technique seems to be highly accurate. These general conclusions are well corroborated by experimental data on a standard gain horn. Sources of errors are outlined and compared with sources of errors in conventional techniques.
TL;DR: In this paper, an aperture model is developed for calculating the radiation field of microstrip antennas, and antenna characteristics, like patterns and radiation resistance, are computed and compared with experimental results.
Abstract: Starting from the equivalence principle, an aperture model is developed for calculating the radiation field of microstrip antennas. In this communication the model is applied to the rectangular microstrip resonator antenna. Antenna characteristics, like patterns and radiation resistance, are computed and compared with experimental results. The model and the calculations include the higher order modes as well as the fundamental mode of the resonator antenna.
TL;DR: In this paper, a general formulation to the problem of the radiation of arbitrary distribution of buried sources within a horizontally stratified anisotropic medium is presented, where the fields are obtained in terms of appropriately defined electric and magnetic types of dyadic Green's functions which are dual to each other.
Abstract: A general formulation to the problem of the radiation of arbitrary distribution of buried sources within a horizontally stratified anisotropic medium is presented. The fields are obtained in terms of appropriately defined electric and magnetic types of dyadic Green's functions which are dual to each other. The formulation is considerably simplified by the resolution of these dyadic Green's functions into transverse electric (TE) and transverse magnetic (TM) waves and by the existing duality between them. A systematic procedure for deriving the fields in an arbitrary layer in terms of the primary source excitation and appropriately defined wave amplitude matrices is described.
TL;DR: The Rayleigh hypothesis in the theory of scattering by a cylindrical obstacle of arbitrary cross section is investigated analytically in this article, where conditions under which the Rayleigh hypotheses are rigorously valid are derived.
Abstract: The Rayleigh hypothesis in the theory of scattering by a cylindrical obstacle of arbitrary cross section is investigated analytically. The hypothesis asserts that outside and on the obstacle the scattered field may be expanded in terms of outward-going wave functions of the circular cylinder. As such, it is analogous to the assumption made by Lord Rayleigh in his treatment of diffraction by a reflection grating. We show that the validity of the Rayleigh hypothesis is governed by the distribution of singularities in the analytic continuation of the exterior scattered field. Conditions are derived under which the Rayleigh hypothesis is rigorously valid. As examples, the elliptic cylinder and the perturbed circular cylinder are considered in detail.
TL;DR: In this article, a method for calculating the electric and magnetic fields from dipoles embedded in anisotropic stratified media is presented. But the method is based on decomposing the fields into transverse electric (TE) and transverse magnetic (TM) modes, which is more computationally efficient than using the Hertz potential.
Abstract: A method is presented for calculating the electric and magnetic fields from dipoles embedded in anisotropic stratified media. By decomposing the fields into transverse electric (TE) and transverse magnetic (TM) modes, the results are obtained more directly and are more computationally efficient than methods using the Hertz potential. The electromagnetic fields are obtained for four types of dipole sources: horizontal electric, horizontal magnetic, vertical electric, and vertical magnetic. The source is embedded within one of several anistropic layers, which are further sandwiched between two semi-infinite media.
TL;DR: In this paper, the principles of using radiating microstrip resonators as elements in a frequency scanning antenna array are described, where the resonators are cascade-coupled, giving a scan of the main lobe due to the phase shift in the resonator in addition to that created by the transmission line phase-shift.
Abstract: The principles of using radiating microstrip resonators as elements in a frequency scanning antenna array are described. The resonators are cascade-coupled. This gives a scan of the main lobe due to the phase-shift in the resonator in addition to that created by the transmission line phase-shift. Experimental results in X -band, in good agreement with the theory, show that it is possible to scan the main lobe an angle of \pm30\deg by a variation of the frequency \pm300 MHz, and where the 3 dB beamwidth is less than 10\deg . The directivity was 14.7 dB, while the gain was 8.1 dB. The efficiency might be improved by a trade-off between the efficiency and the scanning angle, or by using a better amplitude distribution.
TL;DR: In this article, a plane wave incident upon a perfectly conducting linearly oscillating object is investigated both theoretically and experimentally, and the theoretical analysis, accurate to order v/c where v and c are the velocities of object and light, respectively, shows that the target oscillation changes the scattered far field of a motionless target only in phase.
Abstract: The scattering problem for a plane wave incident upon a perfectly conducting linearly oscillating object is investigated both theoretically and experimentally. The theoretical analysis, accurate to order v/c where v and c axe the velocities of object and light, respectively, shows that the target oscillation changes the scattered far field of a motionless target only in phase. The oscillation is assumed to be periodic, and this period is shown to be impressed on the scattered field. Spectral analysis of the modulation shows that the power distribution varies with the shape of the motion, wavelength of the incident field, and the magnitude of the projections of the oscillation in the direction of incidence and receiver. Power spectra have been calculated for square, triangular, and sinusoidal target motion and, in general, the power content in the higher harmonics is found to increase with cartier frequency and magnitude of oscillation. For backscattering from an object moving sinusoidally along the direction of incidence, the power in the first harmonic is shown to exceed that at the carrier frequency when d > 0.23\lambda where d is the magnitude of the oscillation. These calculations are shown to agree with experimental measurements of the phase modulation of the field scattered from a vibrating disk at the X -band. Experimental results were obtained with continuous wave backscatter equipment at 10 GHz that utilized separate tunnel antennas for transmitting and receiving. The receiving section of this equipment was modified to separately display phase modulation and amplitude modulation characteristics of the backscattered signal in both time and frequency, as well as characteristics of the overall modulation envelope. Phase modulations introduced by target oscillations as small as \pm 0.001 in were readily detected, as were amplitude modulations of a few percent.
TL;DR: In this paper, a unique approach for widening the bandwidth of a helical antenna with improved gain, pattern, and axial ratio characteristics is described, which consists of a combination of uniform and tapered helix sections.
Abstract: A unique approach is described for widening the bandwidth of a helical antenna with improved gain, pattern, and axial ratio characteristics. The antenna may be described as a nonuniform or quasi-taper helix, which consists of a combination of uniform and tapered helix sections. Measured patterns, gain, axial ratio, and VSWR for various helical antenna configurations are presented and compared. It is shown that a nonuniform quasi-taper helix can provide an operating bandwidth twice that of a conventional uniform-diameter helix.
TL;DR: In this article, a spectral-domain approach to the inverse problem is considered, and the permittivity profile of an inhomogeneous lossless dielectric slab is reconstructed from multifrequency measurements of the reflection coefficient.
Abstract: A spectral-domain approach to the inverse problem is considered. The permittivity profile of an inhomogeneous lossless dielectric slab is reconstructed from multifrequency measurements of the reflection coefficient. Simple and easy to use analytical relations are obtained. A simple experimental setup has been used, and the results obtained are in good agreement with those predicted by the theory.
TL;DR: In this article, a full-wave approach is proposed to solve the problem of scattering and depolarization by periodic and random rough surfaces, and the solutions are presented in a form that is suitable for use by engineers who may not be familiar with the analytical techniques.
Abstract: Explicit expressions are presented for the radiation fields scattered by rough surfaces. Both electric and magnetic dipole sources are assumed, thus excitations of both vertically and horizontally polarized waves are considered. The solutions are based on a full-wave approach which employs complete field expansions and exact boundary conditions at the irregular boundary. The scattering and depolarization coefficients axe derived for arbitrary incident and scatter angles. When the observation point is at the source these scattering coefficients are related to the backscatter cross section per unit area. Solutions based on the approximate impedance boundary condition are also given, and the suitability of these approximations are examined. The solutions are presented in a form that is suitable for use by engineers who may not be familiar with the analytical techniques and they may be readily compared with earlier solutions to the problem. The full-wave solutions are shown to satisfy the reciprocity relationships in electromagnetic theory, and they can be applied directly to problems of scattering and depolarization by periodic and random rough surfaces.
TL;DR: In this paper, a geometric shaping scheme based on geometric optics for offset-fed dual-reflector antennas is presented, which transforms a ray tube emerging from a symmetric feed horn into a circular beam with a uniform phase and a prescribed radial power distribution on the aperture.
Abstract: A shaping scheme based on geometric optics for offset-fed dual-reflector antennas is presented. A ray tube emerging from a symmetric feed horn is transformed, after reflections, into a circular beam with a uniform phase and a prescribed radial power distribution on the aperture. In this scheme, Snell's law was not imposed on the main reflector. Based on this approximate solution, computer runs were taken for a 5.5-m dish baseline system, and very satisfactory results were obtained. The system so designed not only gives very low sidelobes but also provides a very high aperture efficiency. At 12 GHz an estimated 84 percent of aperture efficiency was achieved in spite of the severe constraint that the ray intersecting the edge of the main reflector meet a -10-dBi criterion.