Showing papers in "IEEE Transactions on Antennas and Propagation in 1986"
TL;DR: In this article, a description of the multiple signal classification (MUSIC) algorithm, which provides asymptotically unbiased estimates of 1) number of incident wavefronts present; 2) directions of arrival (DOA) (or emitter locations); 3) strengths and cross correlations among the incident waveforms; 4) noise/interference strength.
Abstract: Processing the signals received on an array of sensors for the location of the emitter is of great enough interest to have been treated under many special case assumptions. The general problem considers sensors with arbitrary locations and arbitrary directional characteristics (gain/phase/polarization) in a noise/interference environment of arbitrary covariance matrix. This report is concerned first with the multiple emitter aspect of this problem and second with the generality of solution. A description is given of the multiple signal classification (MUSIC) algorithm, which provides asymptotically unbiased estimates of 1) number of incident wavefronts present; 2) directions of arrival (DOA) (or emitter locations); 3) strengths and cross correlations among the incident waveforms; 4) noise/interference strength. Examples and comparisons with methods based on maximum likelihood (ML) and maximum entropy (ME), as well as conventional beamforming are included. An example of its use as a multiple frequency estimator operating on time series is included.
12,446 citations
TL;DR: In this paper, a brief history of near-field antenna measurements with and without probe correction is outlined, beginning with ideal probe scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces.
Abstract: After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.
950 citations
TL;DR: In this paper, a method for the analysis of slot-type discontinuities in microstripline was proposed based on the reciprocity theorem and the exact Green's functions for the grounded dielectric slab in a moment method solution for the unknown antenna currents.
Abstract: A method is presented for the analysis of slot-type discontinuities in microstripline. The approach is based on the reciprocity theorem and uses the exact Green's functions for the grounded dielectric slab in a moment method solution for the unknown antenna currents. The method is applied to two specific geometries: a radiating slot in the ground plane of a microstripline, and an aperture coupled microstrip patch antenna. Results for antenna impedance are compared with measurements, and far-zone patterns are calculated. The method is shown to be quite versatile, and should find application to related problems.
557 citations
TL;DR: In this paper, a method for generating circularly polarized radiation from an array composed of linearly polarized elements having unique angular and phase arrangements is presented, which can significantly reduce the complexity, weight, and RF loss of the array feed.
Abstract: A method is presented for generating circularly polarized radiation from an array composed of linearly polarized elements having unique angular and phase arrangements. With this technique the complexity, weight, and RF loss of the array feed can be significantly reduced, especially in a large array. This uniquely formed array has the capability of generating excellent circular polarization (CP) over a relatively wide frequency bandwidth. In addition, the array is capable of scanning its main beam in the principal planes to relatively wide angles from its broadside direction without serious degradation to its CP quality. Another feature of this uniquely arranged array is a reduction in the occurrence of mutual coupling. The discussion in this paper places special emphasis on the microstrip type of radiator, although the technique presented can be adapted to most types of linearly polarized antenna elements.
508 citations
TL;DR: In this paper, a microstrip patch antenna coupled to a microstripline by an aperture in the intervening ground plane is analyzed and coupled integral equations are formulated by using the Green's functions for grounded dielectric slabs so that the analysis includes all coupling effects and the radiation and surface wave effects of both substrates.
Abstract: A microstrip patch antenna that is coupled to a microstripline by an aperture in the intervening ground plane is analyzed. Coupled integral equations are formulated by using the Green's functions for grounded dielectric slabs so that the analysis includes all coupling effects and the radiation and surface wave effects of both substrates. A Galerkin moment method solution of the coupled integral equations agrees quite well with measured data. Design data are contained in parameter studies, many of which are verified by experimental results.
407 citations
TL;DR: In this paper, an Archimedean planar spiral antenna is numerically analyzed in the presence of a conducting plane reflector, and it is shown that the spiral antenna has two distinct regions in the current distribution, which explain the radiation of a circularly polarized wave for the outer circumference C ranging over about 1.3 λ and C > 2.9 λ, where λ is a free-space wavelength.
Abstract: An Archimedean planar spiral antenna is numerically analyzed in the presence of a conducting plane reflector. The analysis shows that the spiral antenna backed by the plane reflector has two distinct regions in the current distribution, which explain the radiation of a circularly polarized wave for the outer circumference C ranging over about 1.3 \lambda and C > 2.9 \lambda , where \lambda is a free-space wavelength. Further consideration is given to a truncated spiral antenna whose outer circumference is on the order of 1.4 \lambda . The truncated spiral antenna maintains a decaying current distribution and radiates a circularly polarized wave over a 1:1.2 frequency bandwidth. It is also demonstrated that a power gain on the order of 8.5 dB is realized over the same frequency range.
350 citations
TL;DR: In this article, both the Debye-like semi-empirical model and the theoretical Polder-Van Santen mixing model were found to describe adequately the dielectric behavior of wet snow.
Abstract: Microwave dielectric measurements of dry and wet snow were made at nine frequencies betweeo 3 and 18 GHz, and at 37 GHz, using two free-space transmission systems. The measurements were conducted during the winters of 1982 and 1983. The following parametric ranges were covered: 1) liquid water content, 0 to 12.3 percent by volume; 2) snow density, 0.09 to 0.42 g cm-3; 3) temperature, 0 to -5 \deg C and -15\deg C (scattering-loss measurements); and 4) crystal size, 0.5 to 1.5 mm. The experimental data indicate that the dielectric behavior of wet snow closely follows the dispersion behavior of water. For dry snow, volume scattering is the dominant loss mechanism at 37 GHz. The applicability of several empirical and theoretical mixing models was evaluated using the experimental data. Both the Debye-like semi-empirical model and the theoretical Polder-Van Santen mixing model were found to describe adequately the dielectric behavior of wet snow. However, the Polder-Van Santen model provided a good fit to the measured values of the real and imaginary parts of wet snow only when the shapes of the water inclusions in snow were assumed to be both nonsymmetrical and dependent upon snow water content. The shape variation predicted by the model is consistent with the variation suggested by the physical mechanisms governing the distribution of liquid water in wet snow.
348 citations
TL;DR: In this paper, the electromagnetic properties of rectangular microstrip antennas were investigated experimentally, and the bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured.
Abstract: The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured.
347 citations
TL;DR: In this paper, Sarkar et al. describe how the fast Fourier transform (FFT) and conjugate gradient method (CGM) can be used to efficiently make use of the convolutional form of the electric field integral equation for straight wire antennas.
Abstract: In the original paper, (ibid., vol.AP-34, no.5, p.635-40, 1986) T.K. Sarkar et al. describe how the fast Fourier transform (FFT) and the conjugate gradient method (CGM) can be used to efficiently make use of the convolutional form of the electric field integral equation for straight wire antennas. The commentators agree that the CGM converges more rapidly than the previously used method of steepest descent and the spectral iteration technique. They also point out that experience with the dyadic Green's function encountered in the two-dimensional transverse electric (TE) and three-dimensional equations for dielectric bodies is not so encouraging. It is found that for these cases the CGM convergence can be quite slow, degrading the efficiency of the algorithm. In addition, the solution obtained using the pulse-basis point-matching method to discretize the integral equation are very inaccurate for the two-dimensional TE and three-dimensional cases. A reply to these comments from the authors of the original paper is included
323 citations
TL;DR: In this article, a method of moments technique for analyzing electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects is presented based on the combined field integral equations.
Abstract: The recent development and extension of the method of moments technique for analyzing electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects is presented based on the combined field integral equations. The surfaces of the homogeneous three-dimensional arbitrary geometrical shapes are modeled using surface triangular patches, similar to the case of arbitrary shaped conducting objects. Further, the development and extensions required to treat efficiently three-dimensional lossy dielectric objects are reported. Numerical results and their comparisons are also presented for two canonical dielectric scatterers-a sphere and a finite circular cylinder.
315 citations
TL;DR: In this paper, a generalized sidelobe-cancelling structure is employed in which a nonadaptive (conventional) beamformer operates in parallel with an adaptive beamformer, which employs a gradient-based weight adjustment algorithm to minimize output variance subject to a set of J linear constraints on broadband directional derivatives in the desired look direction.
Abstract: An adaptive broad-band beamforming structure is presented which employs a gradient-based weight adjustment algorithm to minimize output variance subject to a set of J linear constraints on broadband directional derivatives in the desired look direction. A generalized sidelobe-cancelling structure is employed in which a nonadaptive (conventional) beamformer operates in parallel with an adaptive beamformer. The conventional portion has a broad-band beampattern which adheres to the specified constraints while the adaptive path is a cascade of a fixed signal blocking matrix and a set of tapped-delay line filters. Blocking is employed to ensure that all incident waveforms which meet the specified constraints do not reach the tapped-delay lines. As a result, an unconstrained least mean square (LMS) power minimization algorithm is employed to adapt the delay line weights. It is shown that with the addition of the directional derivative constraints, the beamformer quiescent bcampattern becomes a function of the location of the phase center used to specify the constraints. A design criterion for choosing this location is suggested and simulation experiments which illustrate the performance of this new adaptive beamformer are presented.
TL;DR: Several methods for synthesis of array antenna patterns with prescribed nulls are reviewed, with attention focused on the characteristic features of the resultant patterns, which provide a perspective on the performance of adaptive antenna systems, which employ these various control architectures.
Abstract: Several methods for synthesis of array antenna patterns with prescribed nulls are reviewed. Methods based on full amplitude/phase control at each array element and methods with a restricted number of degrees of freedom are compared, with attention focused on the characteristic features of the resultant patterns. These features are largely independent of any algorithm for achieving the nulls, and therefore they also provide a perspective on the performance of adaptive antenna systems, which employ these various control architectures.
TL;DR: A detailed analysis of the generalized sidelobe canceller in the presence of array imperfections is discussed, and two new artificial receiver noise injection algorithms are proposed to alleviate the signal nailing problem without seriously compromising jammer nulling.
Abstract: Antenna designers often employ linearly constrained adaptive beamforming as an antijamming measure. With minimal a priori knowledge of the signal environment, this technique nulls out jammers while simultaneously preserving the quality of the main lobe so that a friendly look-direction signal can be received with unity gain. Unfortunately, in the absence of special strategies, linearly constrained adaptive beamforming is hypersensitive to array imperfections when the input signal-to-noise ratio exceeds a certain threshold. This hypersensitivity manifests itself as a nailing of the friendly signal as if it were a jammer. Luckily, the signal nulling problem can be easily remedied by artificial receiver noise injection. A particularly simple and general structure for linearly constrained adaptive beamforming was proposed during the 1970's, and is known as the generalized sidelobe canceller. A detailed analysis of the generalized sidelobe canceller in the presence of array imperfections is discussed, and two new artificial receiver noise injection algorithms are proposed. Computer simulations are included to demonstrate that use of these new algorithms alleviates the signal nailing problem without seriously compromising jammer nulling. For the special case of the Capon maximum-likelihood beamformer, simple approximations are presented for: 1) the Wiener output signal-to-interference-plus-noise ratio ( SINR_{0}\astr ), 2) the antenna element error variance that causes a 3 dB loss of SINR_{0}\astr from its value for an ideal array, and 3) the optimal artificial receiver noise that maximizes SINR_{0}\astr .
TL;DR: In this paper, a hybrid-mode horn antenna has been analyzed theoretically and experimentally, which consists of a conical metal horn with a dielectric core inside, separated from the metal wall by another layer with lower permittivity than for the core material.
Abstract: A hybrid-mode horn antenna has been analyzed theoretically and experimentally. It consists of a conical metal horn with a dielectric core inside, separated from the metal wall by another dielectric layer with lower permittivity than for the core material. It is characterized by a very simple design and excellent electrical performance. The horn can support the balanced hybrid HE 11 -mode, and exhibits low cross polarization and low sidelobes over a wide frequency range. Compared to corrugated horns, the new horn has a simpler design, is easier to analyze, and has the potential of similar cross-polar bandwidth as for corrugated horns with ring-loaded corrugations. Drawbacks are the effects of dielectric losses. Thus the new horn represents an attractive alternative to the corrugated horn antenna.
TL;DR: In this paper, the time delay spread and signal level measurements of 850 MHz radio signals were made over inside-to-outside radio paths at two residential locations and an office building.
Abstract: Time delay spread and signal level measurements of 850 MHz radio signals were made over inside-to-outside radio paths at two residential locations and an office building. Root mean square time delay spreads of up to 420 ns were encountered in residential environments. However, when a direct path was present, this improved to less than 325 ns overall, and even to 100 ns at one residence. Received power levels were around -40 dB, with respect to levels received at 0.3 m antenna separation, Under favorable conditions. In other cases, these relative levels varied from - 40 to - 80 dB. Median signal levels agreed well with continuous wave measurements made earlier at one site. No significant polarization dependence or floor level dependence were seen in these data.
TL;DR: In this article, a beamforming lens with planar arrays of radiating elements interconnected by transmission lines whose length varies as a function of radius is presented, where the back face elements are displaced radially from their corresponding front face elements.
Abstract: A new design for a beamforming lens is presented. Both faces are planar arrays of radiating elements interconnected by transmission lines whose length varies as a function of radius. While the front face elements are regularly spaced, the back face elements are displaced radially from their corresponding front face elements, the amount of displacement also being a function of radius. We show that such a lens is capable of forming low sidelobe beams over an angular sector 36 beamwidths across in all planes of \phi by switching between clusters of only seven feed elements. Because both faces are planar, construction of lightweight lenses for multibeam antennas should be feasible.
TL;DR: In this article, the spectral information is utilized for efficient assignment of a limited number of degrees of freedom in a beam-space constrained adaptive system in order to obtain a stable main beam, retention of low sidelobes, considerably faster response, and reduction in overall cost.
Abstract: Improved spectral estimation techniques hold promise for becoming a valuable asset in adaptive processing array antenna systems. Their value lies in the considerable amount of additional useful information which they can provide about the interference environment, utilizing a relatively small number of degrees of freedom (DOF). The "superresolution" capabilities, estimation of coherence, and relative power level determination serve to complement and refine the data from faster conventional estimation techniques. Two conceptual application area examples for using such techniques are discussed; partially adaptive low-sidelobe arrays, and fully adaptive tracking arrays. For the partially adaptive area the information is utilized for efficient assignment of a limited number of DOF in a beamspace constrained adaptive system in order to obtain a stable main beam, retention of low sidelobes, considerably faster response, and reduction in overall cost. These benefits are demonstrated via simulation examples computed for a 16-element linear array. For the fully adaptive tracking array area the information is utilized in an all-digital processing system concept to permit stable hulling of coherent interference sources in the main beam region, efficient assignment/control of the available DOF, and greater flexibility in time-domain adaptive filtering strategy.
TL;DR: In this article, the optimization problem of radar polarimetry is formulated and the method of finding optimal polarizations is modified and extended to non-reciprocal and bistatic cases.
Abstract: Polarization aspects of the radar target scattering problem are reexamined. The optimization problem of radar polarimetry is formulated and Kennaugh's method of finding optimal polarizations is modified and extended to nonreciprocal and bistatic cases. Our approach does not necessitate diagonalization of the target scattering operator and therefore, a change-of-basis is not required. The change-of-polarization-basis is motivated by the comparison of experimental data taken with different antenna sets. Unitary matrix algebra is used to derive proper transformation formulas for scattering operators and bilinear voltage forms.
TL;DR: In this paper, the fringe current components of the equivalent edge currents are derived for all aspects of illumination and observation, except for the special case where the direction of observation is the continuation of a glancing incident ray propagating "inwards" with respect to the wedge surface (the Ufimtsev singularity).
Abstract: New expressions are derived for the fringe current components of the equivalent edge currents. They are obtained by asymptotic endpoint evaluation of the fringe current radiation integral over the "ray coordinate" measured along the diffracted ray grazing the surface of the local wedge. The resulting expressions, unlike the previous ones, are finite for all aspects of illumination and observation, except for the special case where the direction of observation is the continuation of a glancing incident ray propagating "inwards" with respect to the wedge surface (the Ufimtsev singularity).
TL;DR: In this article, a numerical method for determining the electromagnetic field in the presence of one or several bodies of revolution is presented, where the objects can be made of conductors, dielectrics or their combinations.
Abstract: A numerical method for determining the electromagnetic field in the presence of one or several bodies of revolution is presented. The objects can be made of conductors, dielectrics or their combinations. The excitation is assumed to be due to a plane wave or infinitesimal electric dipoles located within or outside the dielectric. Several formulation types are considered and used to investigate the scattering by different objects. It is found that for moderate values of the dielectric constant, all formulation types give satisfactory results. However, for small or large relative permittivities the solution accuracies depend on the formulation type. As an application of the method to practical problems, two special cases of dielectric rod and microstrip antennas are considered. These antennas have widespread applications and the proposed method can be used to investigate their performance accurately.
TL;DR: In this article, a finite phased array of rectangular microstrip patch antennas is analyzed and the reflection coefficient magnitudes, element patterns and efficiency are calculated for various sized arrays on substrates of practical interest and compared with previous infinite array solutions.
Abstract: Finite phased arrays of rectangular microstrip patch antennas are analyzed. Reflection coefficient magnitudes, element patterns and efficiency (based on power lost to surface waves) are calculated for various sized arrays on substrates of practical interest and are compared with previous infinite array solutions. Measured element patterns and mutual coupling data for a small array are presented and compared with calculations.
TL;DR: Results indicated that all parameters of a source can be measured and the signal waveform can be recovered as well in the presence of other sources less than a beamwidth away.
Abstract: The multiple signal characterization (MUSIC) algorithm is an implementation of the signal subspace approach to compute parameter estimates of multiple point-source signals from the observed voltages received on an array of M antennas. In it, the solution to the multiple source direction finding (DF) problem is provided by the intersection of the signal subspace (obtained from the received data) and the array manifold (obtained via array calibration or prior knowledge of array directional characteristics). The MUSIC algorithm was implemented to experimentally verify the performance of the signal subspace approach to DF under very general scenarios and conditions which are regarded as difficult to impossible in traditional systems. The results of those experiments are described herein. The experimental system consisted of an eight-element antenna array 13 wavelengths in diameter, an eight-channel receiver and digitizer, and a minicomputer with disk storage to process the digitized data. With ideal instrumentation, the MUSIC algorithm provides performance that, as the amount of data collected increases without limit, is asymptotically ideal. However, with finite precision and finite data collection, the performance of even an ideal system can be a sensitive function of source and scenario parameters. Tests demonstrated the resolution of three sources all within one beamwidth (5 \deg ), even when the closer two were spaced less than 0.2 beamwidths. Sources that were polarized differently could be resolved at closer spacings. Experimental DF accuracy was limited by the oncalibrated scattering of source energy from the test range support tower and from the ground. The measured direction of arrival of one source changed by less than 0.01 beamwidths as the other two sources were switched on and off in all combinations. In general, results indicated that all parameters of a source can be measured and the signal waveform can be recovered as well in the presence of other sources less than a beamwidth away.
TL;DR: In this article, the variance and spectrum of amplitude scintillations due to scattering in both turbulent clear air and rain, are investigated and the important aspect of antenna aperture smoothing with special emphasis on earth-space paths and the equations derived are applicable to system design and remote sensing.
Abstract: The variance and spectrum of amplitude scintillations due to scattering in both turbulent clear air and rain, are investigated. Included are the important aspect of antenna aperture smoothing with special emphasis on earth-space paths and the equations derived are applicable to system design and remote sensing. A detailed comparison with published experimental results is carried out and the agreement found is good. Two approaches are described in detail: 1) the point receiver classical wave scattering results are modified to include aperture effects, 2) a scalar scattering cross-section approach is combined with the radar equation and the results derived are similar to those of 1). In addition, approach 2) includes the case of rain. Among the results found it is shown that because the scintillation intensity depends on the ratio between the antenna diameter and the diameter of the Fresnel zone in the turbulent region, low elevation paths counteract the tendency to smoothing by large earth station antennas and the scintillations observed remain large. Also pure scattering induced rain scintillations, even in the millimeter region, are in general reduced to an almost negligible level due to aperture smoothing even though for a theoretical point receiver they would be very intense. The time variability of rain attenuation and its polarization dependence as a source of apparent scintillations are also discussed.
TL;DR: A novel algorithm and architecture are described which have specific application to high performance, digital, adaptive beamforming and have many desirable features for very large scale integration (VLSI) system design.
Abstract: A novel algorithm and architecture are described which have specific application to high performance, digital, adaptive beamforming. It is shown how a simple, linearly constrained adaptive combiner forms the basis for a wide range of adaptive antenna subsystems. The function of such an adaptive combiner is formulated as a recursive least squares minimization operation and the corresponding weight vector is obtained by means of the Q-R decomposition algorithm using Givens rotations. An efficient pipelined architecture to implement this algorithm is also described. It takes the form of a triangular systolic/wavefront array and has many desirable features for very large scale integration (VLSI) system design.
TL;DR: In this article, the numerical solution of a circular microstrip antenna is carried out using the method of moment, and the effect of the probe position, the dielectric permittivity of the substrate and the substrate thickness on the radiation pattern and the mode excitation efficiency are studied.
Abstract: The numerical solution of circular microstrip antenna is carried out using the method of moment. The effect of the probe position, The dielectric permittivity of the substrate, and the substrate thickness on the radiation pattern and the mode excitation efficiency are studied. It is found that the probe position and the patch size can be used to control the mode excitation efficiency, and heigher order modes can be generated using only one feed location. Also, the finite ground plane can be used to improve the symmetry of the radiation patterns. The technique is general and can be used to investigate other scattering and antenna problems involving axisymmetric geometries.
TL;DR: In this article, the combined field integral equation (CFIE) formulation for electromagnetic scattering from perfectly conducting bodies is generalized to treat conductors with layered dielectric coatings, and solutions in terms of two integral operators are developed for body of revolution configurations.
Abstract: The combined field integral equation (CFIE) formulation for electromagnetic scattering from perfectly conducting bodies is generalized to treat conductors with layered dielectric coatings. The generalized formulation is proved to provide unique solutions at all frequencies. The method of moments is used to solve the resulting system of integral equations. Solutions in terms of two integral operators are developed for body of revolution configurations. The behavior and properties of the generalized combined field formulation are illustrated with results of calculations for coated spheres, cylinders, and cones.
TL;DR: In this paper, a planar antenna which can radiate a circularly polarized pencil beam in the x-band is presented for the application of receiving direct broadcast from a satellite, and the measured performance of a model antenna with a diameter of 0.6 m, with a measured antenna gain of about 35 dBi and axial ratio of about 1 dB are realized at 12.2 GHz.
Abstract: Characteristics of a novel planar antenna which can radiate a circularly polarized pencil beam in x -band are presented for the application of receiving direct broadcast from a satellite. This antenna belongs to a class of slotted waveguide antennas and promising performances, especially its high efficiency, have already been predicted theoretically. The measured performance of a model antenna with a diameter of 0.6 m, is presented. Antenna gain of about 35 dBi and axial ratio of about 1 dB are realized at 12.2 GHz; the associated antenna efficiency of 57 percent is very high in comparison with that of the conventional microstrip antennas, in this range of gain.
TL;DR: In this article, a new method for radar target discrimination and identification based on the natural frequencies of the target is presented, which consists of synthesizing aspect-independent discriminant signals, called extinction-pulses (E-Pulses) and singlemode extraction signals which, when convolved numerically with the late-time transient response of an expected target, lead to zero or single-mode responses.
Abstract: A new method of radar target discrimination and identification is presented. This new method is based on the natural frequencies of the target. It consists of synthesizing aspect-independent discriminant signals, called extinction-pulses (E-pulses) and single-mode extraction signals which, when convolved numerically with the late-time transient response of an expected target, lead to zero or single-mode responses. When the synthesized, discriminant signals for an expected target are convolved with the radar return from a different target, the resulting signal will be significantly different from the expected zero or single-mode responses, thus, the differing targets can be discriminated. Theoretical synthesis of discriminant signals from known target natural frequencies and experimental synthesis of them for a complex target from its measured pulse response are presented. The scheme has been tested with measured responses of various targets in the laboratory.
TL;DR: An integral equation based on a plane wave representation of the fields in a simply connected and anisotropic medium has been derived in this article to handle the problem of two-dimensional scattering by a homogeneous anisoustric cylinder.
Abstract: An integral equation based on a plane wave representation of the fields in a simply connected and anisotropic medium has been derived in order to handle the problem of two-dimensional scattering by a homogeneous anisotropic cylinder Its simplicity: one-dimensional, finite range of integration, one unknown with no derivatives of it involved, and a nonsingular kernel, results in an efficient and straightforward numerical implementation Both polarizations are considered and computer results are presented, discussed, and used to check our scheme thoroughly
TL;DR: In this paper, the effect of estimating the spatial correlations while the array is moving is studied in terms of the decorrelation it produces, the change it causes in the eigenvalues of the correlation matrix, and the improvements obtained in the measured spectrum.
Abstract: Spatial spectrum estimation utilizing an array in motion is here investigated for dealing with coherent arrivals in a multiple signal environment. The effect of estimating the spatial correlations while the array is moving is studied in terms of the decorrelation it produces, the change it causes in the eigenvalues of the correlation matrix, and the improvements obtained in the measured spectrum. Cases of both fixed and varying angle of arrival are investigated, The former arises with distant sources and will, with a sufficiently long estimation interval, emulate uncorrelated sources and given correspondingly sharp spectra. The latter arises with nearby sources and will allow them to be distinguished but will be attended by spectral shift and broadening, and loss of resolution. It is shown that meaningful estimates of the arrival angles can nevertheless be made. Specific illustrations are worked out using a seven-element, sparse, nonuniformly spaced linear array utilizing the well-known superresolution spectral estimators-the maximum likelihood (ML) method, the method of linear prediction (LP), and the method of multiple signal classification (MUSIC).