Showing papers in "IEEE Transactions on Antennas and Propagation in 1978"
TL;DR: In this paper, the empirical relation A = aR^{b} between the specific attenuation A and the rain rate R is used in the calculation of rain attenuation statistics.
Abstract: Because of its simplicity, the empirical relation A = aR^{b} between the specific attenuation A and the rainrate R is often used in the calculation of rain attenuation statistics. Values for the frequency-dependent parameters a and b are available, however, for only a limited number of frequencies. Some of these values, furthermore, were obtained experimentally, and may contain errors due to limitations in the experimental techniques employed. The aR^{b} relation is shown to be an approximation to a more general relation, except in the low-frequency and optical limits. Because the approximation is a good one, however, a comprehensive and self-consistent set of values for a and b is presented in both tabular and graphical form for the frequency range f = 1-1000 GHz. These values were computed by applying logarithmic regression to Mie scattering calculations. The dropsize distributions of Laws and Parsons, Marshall and Palmer, and Joss et al., were employed to provide calculations applicable to "widespread" and "convective" rain. Empirical equations for some of the curves of a(f) and b(f) are presented for use in systems studies requiring calculations at many frequencies. Some comparison is also made with experimental results, and suggestions are given regarding application of the various calculations.
674 citations
TL;DR: The radiation characteristics of an N -port antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports, and the direction of maximum gain can becontrolled by varying the load reactances.
Abstract: The radiation characteristics of an N -port antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports. Reactive loads can be used to resonate a real port current to give a radiation pattern of high directivity. The theory of resonance is extended to include complex port currents and impedance loads. The initial design of an array is obtained by resonating a desired port current vector, which is then improved by an optimum seeking univariate search method. The direction of maximum gain can be controlled by varying the load reactances. Several numerical examples are given for a circular array of seven dipole elements.
450 citations
TL;DR: In this article, an analytical approach to the problem of scattering by composite random surfaces is presented, where the surface is assumed to be Gaussian so that the surface height can be split (in the mean-square sense) into large and small scale components relative to the electromagnetic wavelength, and a first-order perturbation approach developed by Burrows is used wherein the scattering solution for the large-scale structure is perturbed by the small-scale diffraction effects.
Abstract: An analytical approach to the problem of scattering by composite random surfaces is presented. The surface is assumed to be Gaussian so that the surface height can be split (in the mean-square sense) into large ( \zeta_{l} ) and small ( \zeta_{s} ) scale components relative to the electromagnetic wavelength. A first-order perturbation approach developed by Burrows is used wherein the scattering solution for the large-scale structure is perturbed by the small-scale diffraction effects. The scattering from the large-scale structure (the zeroth-order perturbation solution) is treated via geometrical optics since 4k_{0}^{2}\bar{\zeta_{l}^{2}} \gg 1 . The first-order perturbation result comprises a convolution in wavenumber space of the height spectrum, the shadowing function, a polarization dependent factor, the joint density function for the large-scale slopes, and a truncation function which restricts the convolution to the domain corresponding to the small-scale height spectrum. The only "free" parameter is the surface wavenumber separating the large and small height contributions. For a given surface height spectrum, this wavenumber can be determined by a combination of mathematical and physical arguments.
306 citations
TL;DR: In this article, the application of the Lorentz reciprocity theorem to the problem of determining antenna characteristics, including the far-field pattern, is presented and the data required to correct for the directional effects of the probe, the effect of probe correction on the measured data, and the attendant mathematical computations in rectangular systems are described.
Abstract: The general problem concerning the interaction of a probe antenna with the near field of an arbitrary antenna is considered. The application of the Lorentz reciprocity theorem to the problem of determining antenna characteristics, including the far-field pattern, is presented. The data required to correct for the directional effects of the probe, the effect of probe correction on the measured data, and the attendant mathematical computations in rectangular systems are described. Extensions to cylindrical and spherical systems are discussed.
261 citations
TL;DR: In this article, a theory enlarges on Stevenson's method, and uses a modified form of Booker's relation based on Babinet's principle to treat nonresonant longitudinal shunt slots in the broad wall of a rectangular waveguide.
Abstract: The differences in mutual coupling for a central slot and a peripheral slot cannot be ignored in small arrays if good patterns and impedance are to be obtained. A theory has been developed whereby the length and offset of every slot in the array can be determined, in the presence of mutual coupling, for a specified aperture distribution and impedance match. The theory enlarges on Stevenson's method, and uses a modified form of Booker's relation based on Babinet's principle to treat nonresonant longitudinal shunt slots in the broad wall of a rectangular waveguide. A general relation between slot voltage and mode voltage is developed, and then formulas are derived for the active, self-, and mutual admittances among slots. These formulas result in a design procedure. Analogous treatments of inclined series slots in rectangular guide and of strip-line-fed slots are possible. Comparison between various experiments and the theory is presented. Tests of the theory include the resonant length of a zero offset slot, resonant conductance versus offset and resonant conductance versus frequency for a single slot, and self- and mutual admittances for two staggered slots. The design and performance of a two-by-four longitudinal shunt slot array is also described.
233 citations
TL;DR: In this paper, a tutorial review of a number of methods for analyzing such aperture problems is presented with an emphasis on techniques, and an extensive set of representative numerical results is included. But the discussion presented herein is reasonably self-contained and is supplemented by references to classical as well as current approaches to the aperture problem.
Abstract: In designing hardened systems, one must be able to characterize as well as quantitatively determine the penetration of EMP signals through apertures of general shapes in structures of varying configurations. In this paper a tutorial review of a number of methods for analyzing such aperture problems is presented with an emphasis on techniques. The discussion presented herein is reasonably self-contained and is supplemented by references to classical as well as current approaches to the aperture problem. An extensive set of representative numerical results is included.
220 citations
TL;DR: In this paper, the extension of Prony's method to allow multiple poles, the development of techniques for determining the number of poles contained in the transient data, and the effects of noise in the data on the numerical procedures are studied.
Abstract: Three difficulties associated with Prony's method are studied. These are the extension of the method to allow multiple poles, the development of techniques for determining the number of poles contained in the transient data, and the effects of noise in the data on the numerical procedures. Solutions to these difficulties are studied, and numerical samples are presented.
187 citations
TL;DR: In this article, a theoretical treatment of the rectangular microstrip radiating element has been performed, where the element was modeled as a line resonator with radiation taking place at the open-circuited ends.
Abstract: A theoretical treatment of the rectangular microstrip radiating element has been performed. The element has been modeled as a line resonator with radiation taking place at the open-circuited ends. This has been verified by using a liquid crystal visual detector. With the simplified model, the input impedance and the far fields have been calculated for different resonant modes. The interaction between the radiating ends will effect the input impedance, and this has been considered by defining a mutual conductance. Also, a mutual conductance between microstrip elements has been expressed in far-field quantities and plotted as a function of spacing along the E - and H - planes. The directivity of an isolated element has been calculated as the directivity of one radiating end times the contribution due to the array factor.
187 citations
TL;DR: A moment method solution to the problem of radiation or scattering from geometries consisting of open or closed surfaces, wires, and wire/surface junctions is presented in this article.
Abstract: A moment method solution to the problem of radiation or scattering from geometries consisting of open or closed surfaces, wires, and wire/surface junctions is presented. The method is based on the sinusoidal reaction formulation. Several examples of input impedance calculations illustrate the versatility, accuracy, and computational efficiency of the method.
159 citations
TL;DR: In this paper, the stability of the numerically computed estimate of the backscattered average power depends on N, the total number of disjoint surface segments averaged; \Delta x, the spacing between surface current points; D, the width of each surface segment; and g, the wide width of the window function.
Abstract: A one-dimensionally rough random surface with known statistical properties was generated by digital computer. This surface was divided into many segments of equal length. The moments method was applied to each surface segment assuming perfect conductivity to compute the induced surface current and subsequently the backscattered field due to an impinging plane wave. The return power was then calculated and averaged over different segments. Unlike numerical computations of scattering from deterministic surfaces, problems of stability (as defined by Blackman and Turkey [11]) and convergence of the solution exist for random surface scattering. It is shown that the stability of the numerically computed estimate of the backscattered average power depends on N , the total number of disjoint surface segments averaged; \Delta x , the spacing between surface current points; D , the width of each surface segment; and g , the width of the window function. Relations are obtained which help to make an appropriate choice of these parameters. In general, choices of \Delta x, D , and g are quite sensitive to the incident wavelength and the angular scattering properties of the surface.
149 citations
TL;DR: A review of the theory of field behavior near a dielectric wedge is presented in this paper, where the static results give an accurate account for the rate of growth of the fields in the singular cases, but some disagreement in nonsingular cases.
Abstract: A review of the theory of field behavior near a dielectric wedge is presented. An overview of the static results is given, and it is shown that the series of Meixner for the dynamic case in general is nonexisting. Numerical results for scattering by a dielectric cylinder of square cross section indicate that the static results give an accurate account for the rate of growth of the fields in the singular cases, but some disagreement in nonsingular cases.
TL;DR: The electromagnetic pulse (EMP) produced by the gamma rays from nuclear explosions is discussed in this article, where an approximate method of solving the equations is described by considering time regimes in which various terms in the equations are negligible, e.g., either the conduction current or displacement current can be dropped.
Abstract: The electromagnetic pulse (EMP) produced by the gamma rays from nuclear explosions is discussed. The gamma rays produce a current of Compton recoil electrons, and these electrons produce further ionization so that the air becomes conducting. The Compton current leads to the generation of electromagnetic fields according to Maxwell's equations. The conductivity tends to limit the magnitude of the fields. Approximate methods of solving the equations are described by considering time regimes in which various terms in the equations are negligible, e.g., either the conduction current or the displacement current can be dropped. Further advantage is obtained by replacing the transverse fields by outgoing and ingoing waves; outgoing waves are dominant at early times. Features of the solutions are described for nuclear bursts at the ground surface and at high altitude. The history of EMP is reviewed briefly.
TL;DR: In this paper, the theory of near-field measurements for antenna practitioners is summarized, and the measurement procedures in three coordinate systems, namely rectangular, cylindrical, and spherical are outlined.
Abstract: The theory of near-field measurements for antenna practitioners is summarized, and the measurement procedures in three coordinate systems, namely rectangular, cylindrical, and spherical are outlined. Specific topics include probe characterization, measurement systems, data reduction, and attendant accuracies. The results of recent studies are also summarized, and some brief remarks on future applications of near-field measurements in the laboratory, the production line, and in field testing and evaluation conclude the paper.
TL;DR: In this article, an application of the Backus-Gilbert methodology is made to obtain an objective criterion of the best resolution (in a least squares sense) obtainable from a given system and to investigate the trade-off between resolution and noise in the derived average brightness temperatures.
Abstract: In the analysis of antenna temperature maps of the earth obtained by satellite-borne microwave radiometers, estimates of brightness temperatures or averages of brightness temperatures over areas considerably smaller than the region sensed at a given position of the radiometer antenna are often needed. An application of the Backus-Gilbert methodology is made to obtain an objective criterion of the best resolution (in a least squares sense) obtainable from a given system and to investigate the trade-off between resolution and noise in the derived average brightness temperatures. The mathematically related problem of simultaneously analyzing antenna temperature measurements made at different frequencies by antennas with noncoincident antenna patterns is also considered.
TL;DR: In this article, the authors summarized the various sensor designs developed to achieve this in an optimal manner and summarized the different sensor designs for use either in a free space or in a system under test in such a simulator.
Abstract: For measuring transient electromagnetic fields and related quantities, one needs accurate broadband sensors with simple transfer functions. The various sensor designs developed to achieve this in an optimal manner are summarized. Such sensors are designed for use either in a "free space" environment (such as in an EMP simulator or on a system under test in such a simulator) or in a nuclear source region that includes local source current and perhaps conductivity. There are now numerous designs which have been iterated for improvements over the last decade.
TL;DR: In this paper, the effects of horn aperture size, slot width-to-pitch ratio and frequency on the cross-polarization of the radiation pattern are considered, as well as the range of slot parameters which can be used and the design of the slots near the throat of the horn to achieve a low VSWR for bandwidths of 1.5 to 1.
Abstract: Details of the design of circumferentially corrugated conical horns are presented. Radiation pattern and phase-center characteristics for both "wide-band" and "narrow-band" horns are considered, and a comparison is made between the relative sizes of the two types of horns. The effects of horn aperture size, slot width-to-pitch ratio and frequency on the cross-polarization of the radiation pattern are included. The range of slot parameters which can be used and the design of the slots near the throat of the horn to achieve a low VSWR for bandwidths of 1.5 to 1 are also considered. The results of measurements on horns with both narrow and wide included angles are given.
TL;DR: A data processing technique, namely Prony's method, is evaluated and the use of the algorithm for EMP and other transient problems is illustrated and the relationship between the waveform parameterization and the singularity expansion method (SEM) is described.
Abstract: A data processing technique, namely Prony's method, is evaluated. The use of the algorithm for EMP and other transient problems is illustrated and the relationship between the waveform parameterization and the singularity expansion method (SEM) is described. The impulse response of a synthesizer network is obtianed using Prony processing of the output of the double exponential excited circuit. Difficulties which arise in this type of processing such as rank deficiency, aliasing, and noise effects are considered and methods for alleviation such as filtering and rank-overspecification are introduced and evaluated. The overall status of waveform parameterization as applied to SEM is considered and suggestions for future research presented.
TL;DR: An approach, based on the theory of the Radon transform is used here to show that this problem of radar identification of perfectly conducting targets is equivalent to the problem of image reconstruction from projections, which has been solved in many diverse disciplines.
Abstract: In radar identification of perfectly conducting targets, a need arises to determine a convex body from its cross-sectional areas normal to the lines of sight for a number of view angles. An approach, based on the theory of the Radon transform is used here to show that this problem is equivalent to the problem of image reconstruction from projections, which has been solved in many diverse disciplines. Two of the inversion algorithms developed in these fields are used to estimate object shapes from their cross-sectional areas, obtainable from the objects' far-field, backscattered ramp responses.
TL;DR: In this paper, the effects of dielectric slabs on both sides of the array were investigated and it was shown that these effects can reduce or eliminate the unwanted changes in resonant frequency and bandwidth.
Abstract: The applications of arrays of rectangular slots have been severely limited since their resonant frequency (where unity transmission occurs) and bandwidth change with incident angle. By utilizing a modal analysis solution which includes the effects of dielectric slabs on both sides of the array, we show that these dielectric effects can, with proper design, reduce or eliminate the unwanted changes in resonant frequency and bandwidth. The presence of the dielectric slabs also cause other changes in the transmission curves. Two of these changes are the occurrence of the Wood's anomaly ("blind angle") null at a lower frequency, and additional narrow resonances in the transmission curves. These phenomena are explained by considering the behavior of the Floquet modal impedances in the presence of the dielectric layer.
TL;DR: In this article, a relatively short cylindrical antenna with continuously tapered resistive loading has been studied for the purpose of picosecond pulse measurements, and the experimental results indicate excellent linear amplitude and phase response over the frequency range.
Abstract: A relatively short cylindrical antenna with continuously tapered resistive loading has been studied for the purpose of picosecond pulse measurements. The antenna considered is a nonconducting cylinder with continuously deposited varying-conductivity resistive loading. The current distributions on the antenna were numerically calculated using the method of moments. Using these current distributions, other quantities such as input admittance, near-field and farfield radiation patterns, and radiation efficiency, were also numerically calculated and compared with the results using the Wu-King's approximate current distribution. Agreement is relatively good except at high frequencies kh > \pi/2 where the method of moments appears to give better results. To verify the theoretical results, several resistively loaded antennas were fabricated, and their picosecond pulse receiving characteristics were analyzed for the frequency range between 5 kHz and 5 GHz. The experimental results indicate excellent linear amplitude and phase response over the frequency range. This provides the unique capability of this antenna to measure fast time-varying electromagnetic fields with minimal pulse-shape distortion due to nonlinear amplitude or phase characteristics.
TL;DR: In this paper, a class of two simultaneous Wiener-Hopf equations is reduced to the factorization and decomposition of scalar functions, and it has been shown that the problems previously solved by the Hilbert-Hurd method lead to WienerHopf systems that belong to this class.
Abstract: A class of two simultaneous Wiener-Hopf equations is reduced to the factorization and the decomposition of scalar functions. In particular, it has been shown that the problems previously solved by the Hilbert-Hurd method lead to Wiener-Hopf systems that belong to this class.
TL;DR: In this paper, an electromagnetic plane wave by an infinite slit in a conducting screen of finite thickness is studied theoretically using Weber-Schafheitlin discontinuous integrals, where the direction of the incident wave is assumed to be in a plane perpendicular to that of the screen, and both polarizations are treated.
Abstract: Diffraction of an electromagnetic plane wave by an infinite slit in a conducting screen of finite thickness is studied theoretically using Weber-Schafheitlin discontinuous integrals. The direction of the incident wave is assumed to be in a plane perpendicular to that of the screen, and both polarizations are treated. The problems are reduced to simulataneous equations with an infinite number of unknowns, which are truncated in actual numerical computation. Numerical results for transmission coefficients are compared with those calculated from the Mathieu function expansion, and fairly good agreement is obtained. Far-field patterns are measured experimentally for the E -Polarization using a parallel-plate waveguide. The measured results confirm the validity of the theoretical prediction.
TL;DR: The selection of auxiliary elements for partially adaptive antenna arrays for the purpose of optimizing performance in a multiple narrow-band jammer environment is studied and an explicit solution for the two-jammer problem is derived.
Abstract: The selection of auxiliary elements for partially adaptive antenna arrays for the purpose of optimizing performance in a multiple narrow-band jammer environment is studied. An explicit solution for the two-jammer problem is derived. This case is sufficient to illustrate the interaction of multiple jammers and at the same time affords a degree of understanding of more complex problems. Computer solutions are also presented and discussed for several line array and planar array configurations.
TL;DR: In this paper, a circuit representation for the impedance of spherical waves radiating from a spherical boundary was derived using a partial fraction expansion by Chu in order to establish gain bandwidth limitations for antennas.
Abstract: A circuit representation for the impedance of spherical waves radiating from a spherical boundary was derived using a partial fraction expansion by Chu in order to establish gain bandwidth limitations for antennas. These circuits are derived directly from the recurrence relations for spherical Bessel functions. They provide an exact analog of the field solution both inside and outside of a spherical surface for any values of permittivity ( \epsilon ) and permeability ( \mu ). Since the circuits have the form of high-pass filters, they provide significant physical insight into scattering and radiation problems, suggest suitable asymptotic or approximate forms and allow circuit concepts and theorems to be brought to bear in order to solve specific configurations or to set general performance bounds. As an example of their application, compact computer programs for the radar cross section of conducting and dielectric spheres, the minimum Q 's for antennas, the Q 's and resonant frequencies of dielectric spheres and the induced current at the specular and shadow points of a conducting sphere are given. Other illustrative results are the short pulse responses of a solid dielectric and a dielectric-coated sphere computed using the circuit surge impedance and multiple reflection terms; and the response of a hypothetical scatterer in which the TE and TM modes are coupled.
TL;DR: In this article, an iteration method is presented for calculating the distances between the elements of a symmetrical non-uniformly spaced linear array antenna for sidelobe reduction, where the amplitude of the excitation is assumed to be constant.
Abstract: The material discussed can be divided into two parts. In the first part, an iteration method is presented for calculating the distances between the elements of a symmetrical nonuniformly spaced linear array antenna for sidelobe reduction. The amplitude of the excitation is assumed to be constant. The iteration method is applied to linear array consisting of 24 elements. After a few iterations, the sidelobe-to-mainlobe power ratio was reduced to over 22 dB from its value of 13.2 dB for uniform array spacing. In the second part, several symmetrical nonuniformly spaced planar array antennas have been designed, using the nonuniform linear array spacings of part one. The planar arrays include square-shaped and circular structures, with the number of elements ranging from 284 to 576. The iteration method discussed can be applied to linear arrays with any number of elements to obtain nonuniform grid spacings for sidelobe reduction. A number of planar grid structures can be constructed using the nonuniform linear grids. The nonuniform linear and planar arrays utilize fewer radiating elements and result in desirable sidelobe structures.
TL;DR: In this article, alternative representations are obtained for the high-frequency surface field excited on a perfectly conducting concave circular cylinder by an axial magnetic line current located on the surface.
Abstract: Alternative representations are obtained for the high-frequency surface field excited on a perfectly conducting concave circular cylinder by an axial magnetic line current located on the surface. Included are ray-optical, canonical integral, whispering gallery mode, and near-field formulations, and various combinations of these. Asymptotic evaluations in different parameter ranges lead to results with varying accuracy and physical content. Their utility is assessed by extensive numerical calculations and comparisons. Most intriguing is a form of the asymptotic solution that involves only a number of geometric optical rays and a number of whispering gallery modes.
TL;DR: In this paper, the authors examined the limited aperture problem of physical optics inverse scattering via the method of multidimensional stationary phase and showed that target information is recoverable from bandlimited and aspect-limited scattering data.
Abstract: The limited aperture problem of physical optics inverse scattering is examined via the method of multidimensional stationary phase. It is shown that target information is recoverable from bandlimited and aspect-limited scattering data. Numerical examples are presented for the case of a perfectly reflecting circular cylinder.
TL;DR: Numerical data is presented which illustrate trade-offs between array size, directive gain, SNR, efficiency, bandwidth, tolerances, and farfield patterns and the results of an experimental study are found in good agreement with theoretical predictions.
Abstract: Some of the characteristics of arrays designed for maximum directive gain subject to a tolerance constraint are described. Numerical data are presented which illustrate trade-offs between array size, directive gain, SNR, efficiency, bandwidth, tolerances, and farfield patterns. The results of an experimental study are found to be in good agreement with theoretical predictions.
TL;DR: In this paper, the development of a novel L-band microstrip phased array for aircraft is described, and the array is electronically steerable in elevation, conformal to the surface of an aircraft, 0.14in thick, low cost in production quantities, installed without cutting large holes in the aircraft, and capable of 12dB gain relative to right hand circular isotrope.
Abstract: The development of a novel L -band microstrip phased array for aircraft is described. The array is electronically steerable in elevation, conformal to the surface of an aircraft, 0.14-in thick, low cost in production quantities, installed without cutting large holes in the aircraft, and capable of 12-dB gain relative to right hand circular isotrope. The microstrip radiating element is described, and its operation is explained. The array design is considered in relation to ground plane curvature, grating lobes, sidelobes, beam shape and gain. A technique for obtaining 30\deg phase resolution from 3-bit phase shifters is presented. The design of simple loaded line and switched line phase shifters is reported.
TL;DR: In this article, surface integral representations for electromagnetic wave scattering from dielectric bodies are derived, and the interior resonant solutions, the cause of erroneous solutions, accompanied with the equations presented here and the removal of these solutions are briefly discussed.
Abstract: The surface integral representations are derived for electromagnetic wave scattering from dielectric bodies. Several kinds of integral equations are given for dielectric cylinders immersed in an obliquely incident wave. The interior resonant solutions, the cause of erroneous solutions, accompanied with the equations presented here and the removal of these solutions are briefly discussed.