Diffraction of a plane electromagnetic wave by a two-layer finite array of small bodies of revolution

A three-dimensional vector problem of plane-wave diffraction by a two-layer finite array of perfectly conducting bodies of revolution is considered. The problem is solved under the assumption that the sizes of the elements of the array are small as compared to the wavelength. The approach proposed was tested by comparing the far-field patterns of an array with a small number of elements, calculated by two different methods. Angular dependences of the far-field patterns of arrays of elements in the form of spheres, oblate spheroids, and superellipsoids of revolution are constructed. Dependences of the plane-wave reflection and transmission coefficients on the angle of incidence for single-row finite and infinite arrays are presented.     

Passive Localization of Mixed Near-Field and Far-Field Sources Using Two-stage MUSIC Algorithm

Passive source localization is one of the issues in array signal processing fields. In some practical applications, the signals received by an array are the mixture of near-field and far-field sources, such as speaker localization using microphone arrays and guidance (homing) systems. To localize mixed near-field and far-field sources, this paper develops a two-stage MUSIC algorithm using cumulant. The key points of this paper are: (i) in the first stage, this paper derives one special cumulant matrix, in which the virtual ?steering vector? is the function of the common electric angle in both near-field and far-field signal models so that source direction-of-arrival (DOA) (near-field or far-field one) can be obtained from this electric angle using the conventional high-resolution MUSIC algorithm; (ii) in the second stage, this paper derives another particular cumulant matrix, in which the virtual ?steering matrix? has full column rank no matter whether the received signals are multiple near-field sources or multiple far-field ones or their mixture. What is more important, the virtual ?steering vector? can be separated into two parts, in which the first one is the function of the common electric angle in both signal models, whereas the second part is the function of the electric angle that exists only in near-field signal model. Furthermore, by substituting the common electric angle estimated in the first stage into one special Hermitian matrix formed from another MUSIC spectral function, the range of near-field sources can be obtained from the eigenvector of the Hermitian matrix. The resultant algorithm avoids two- dimensional search and pairing parameters; in addition, it avoids the estimation failure problem and alleviates aperture loss. Simulation results are presented to validate the performance of the proposed method.     

Evaluation of adaptive phased array antenna, far-field nullingperformance in the near-field region

A theory for analyzing the behavior of adaptive phased array antennas illuminated by a near-field interference test source is presented. Conventional phased array near-field focusing is used to produce an equivalent far-field antenna pattern at a range distance of one to two aperture diameters from the adaptive antenna under test. The antenna is assumed to be a linear array of isotropic receive elements. The interferer is assumed to be a bandlimited noise source radiating from an isotropic antenna. The theory is developed for both partially and fully adaptive arrays. Results are presented for the fully adaptive array case with single and multiple interferers. The results indicate that near-field and far-field adaptive nulling can be equivalent. The adaptive nulling characteristics studied in detail are the array radiation patterns, adaptive cancellation, covariance matrix eigenvalues, and adaptive array weights     

Active antenna array lumped ring configuration

Coupled active antenna oscillator arrays are used for power-combining at microwave and millimeter-wave frequencies. It is known that the relative phase determined by the element separation distance ultimately determines the array operational mode and, hence, far-field radiation characteristics. Separately, it is known that coupled oscillator modal stability is achieved by coupling oscillators through lumped capacitive elements. In this paper, an arrangement whereby lumped capacitive elements (placed across the oscillator loads) and radiative coupling are employed concurrently is investigated. The arrangement takes the form of a ring of coupled oscillators used to excite a 2×2 antenna array. The effect that these couplings have on array behavior are evaluated using time-domain analysis and analytically derived equations. Experimental results for far-field radiation patterns are discussed in relation to coupled oscillator dynamical behavior. These suggest that the theoretical predictions are valid, offering a robust design tool for studies of larger power-combining arrays     

阵列光束的偏振方向对其相干合成远场光强分布的影响

理论推导了线偏振光纤激光器阵列相干合成远场光强分布的表达式,详细研究了激光器的偏振方向对相干合成远场图样分布、中心主瓣的角宽度以及相干合成远场条纹可见度的影响.阵列光束偏振方向的不一致会使相干合成远场光强的峰值功率下降,中心主瓣的宽度增加,远场光强分布有本底漂移,远场条纹可见度下降.     

Scattering by an Arbitrary Array of Parallel Wires

Equations are developed for the scattering pattern of an arbitrary array of parallel wires. The wires are assumed to be infinitely long, perfectly conducting, and very small in diameter in comparison with the wavelength. The incident wave is assumed to be TM with respect to the wire axis, but it may have normal or oblique incidence on the wires. The solution includes the interaction effects among all the wires. The far-field scattering patterns are presented graphically for plane arrays, circular arrays, semicircular arrays, square arrays, and other configurations. If a sufficiently great number of wires is present, it is shown that the scattering pattern approaches that of a solid conducting cylinder of the same cross-section shape as the wire-grid array.     

Y-Junction semiconductor laser arrays: Part II--Experiments

Laser arrays employingY-junctions to coherently couple the emitters in-phase have been fabricated by metalorganic chemical vapor deposition. The far-field patterns are stable and centered normal to the facet. They are typically multilobed in accordance with the diffraction pattern of multiple emitters. By the use of flared waveguides near the facets the near-field fill factor can be increased to greater than 80 percent. This modification concentrates the radiation in the central diffraction lobe. Power outputs of 200 mW CW have been obtained from a ten element array of 1.5μm wide emitters.     

Analysis of injection-locked gain-guided diode laser arrays

A new model for injection-locked gain guided laser arrays is proposed. Diffraction-limited and single-lobe operation of injection-locked arrays is attributed to coherent summation of several transverse modes that are phase locked by injection. The model predicts far-field and near-field patterns, locking bandwidth, beam-steering properties, and locked output power. The effects of varying the master power, beam shape, position, and incidence angle on the slave array facet are also studied. Theoretical and experimental results are compared     

Patterns and polarizations of simultaneously excited planar arrays on a conformal surface

A conformal array on a surface of small curvature can be approximated by a number of planar arrays, several of which may be excited simultaneously so as to achieve a performance similar to that of a conformal array. Since the main beam of a planar array can be steered to any direction in the visible Space, several arrays, each oriented in a different direction, can be steered cooperatively to form a single beam in a desired direction. A general formulation of the radiation field of such an array of arrays is developed with the aid of vector recomposition formulas between two orthogonal co-ordinate systems. This formulation does not involve the integration of the current source but is solely dependent upon the knowledge of the far-field expressions of elementary radiators. Using this formulation, it can be shown that within each array, the conventional row and column phase setting can be used, although each array requires an additional phase shift to compensate for the phase difference caused by its position on the curved surface. As examples, the radiation patterns and polarizations of multiple arrays of short dipoles are studied using the present formulation. A comparison of the multiple planar arrays with the conventional conformal array is also presented.     

Synthesis of near-field patterns of arrays

A new technique of synthesis of near-field (NF) amplitude and phase patterns of linear, planar, of volume arrays of finite size or arrays located on a planar contour of finite size is presented. The array could consist of point dipoles or directive elements. The criterion for prescribing the NF (amplitude and phase) pattern information in the synthesis problem for unique determination of array excitation currents is also stated. The proposed near-field synthesis technique is based on the potential integral solution of source currents, Nyquist sampling of the near-field data and the technique of linear least square approximation (LLSA). The NF pattern synthesis technique is illustrated to synthesize a variety of NF patterns with a number of array configurations. Application of the proposed NF pattern synthesis technique to minimize distortion in far-field patterns of arrays mounted on a conducting platform and to realize array antennas with low sidelobes in the near and far field is also presented.     

Mode locking of individual array modes of a gain-guidedsingle-quantum-well laser array with an external mirror

Mode locking of individual spatial lateral array modes of gain-guided GaAs single-quantum-well laser array with an external mirror is observed. The single-lobe fundamental array mode and several higher order array modes were individually selected by adjusting the external mirror. The array modes were characterized by the far-field patterns of the laser array. The corresponding spectrum consists a number of narrow longitudinal modes indicating that a single array mode was selected. These array modes were mode locked using a combination of feedback from the external mirror and sinusoidal RF modulation. The far-field patterns remained spatially constant when the RF modulation was applied. Autocorrelation pulsewidth measurements showed that the pulses have a Gaussian shape. Pulses as short as 70 ps were obtained for the lowest order array mode, where all the laser emitters were in phase, and increase with increasing array mode order     

Paraxial-misalignment insensitive external-cavitysemiconductor-laser array emitting near-diffraction limited single-lobedbeam

We present a novel easy-to-align external cavity configuration for efficiently obtaining a near-diffraction limited single-lobed beam from gain-guided laser diode arrays. The external cavity has an external mirror (EM) in the image plane of the array. Two bulk-optics experimental setups are evaluated and a compact GRIN lens design is discussed. There are several advantages for the present geometry, including orders of magnitude lower misalignment-sensitivity and superior mode discrimination. Both experimental setups deliver near-diffraction limited single-lobed beams (of width ~0.8° at the rated output power of 100 mW of the array) in the entire current range. The light-current (L-I) characteristic is linear and kink-free and one of the setups shows higher efficiency than the free-running array. The broad-area laser (BAL) mode theory is discussed, introducing radiation losses to the analysis. Several aspects of amplification in laser arrays are theoretically explained, such as why the optimum angle of the far-field lobe is always greater than the tenth mode angle (for a uniform 10-stripe array). It is shown that the gain of the amplifying medium broadens the far-field profile. The width of the far-field lobe increases with gain and decreases with the lobe angle. An analytical expression for the broadened far-field profile of BAL modes is presented. The theory compares very well with the experiments     

Nonlinear analysis of Y-junction laser arrays

An analysis of Y-junction arrays above threshold is presented. The analysis incorporates nonlinear gain saturation and shows that the gain becomes nonuniform above threshold even if the array is otherwise ideal. The nonuniform, nonlinear gain saturation causes the near field and the radiation patterns to deteriorate with increasing output power. Although the far-field lobe width does not necessarily increase greatly above threshold, the Strehl ratio may decrease significantly depending on the device design. Empirically, it is found that, when the Strehl ratio decreases to approximately 0.7, the second-order array mode attains threshold and both the first and second array modes lase simultaneously. An improved design, whose far-field Strehl ratio remains 0.85 even well in excess of 1 W output power and in which the second-order array mode never attains threshold, is discussed     

A simplified computational procedure for the analysis of planar arrays

A simplified procedure for inverting the mutual impedance matrix of a uniform-spaced planar array of dipoles is presented. It relies on the special features of this matrix being symmetric block-Toeplitz and having a nilpotent off-diagonal part. Active radiation impedances and voltage standing-wave ratio (VSWR) values are then evaluated for various element positions and scan angles. The array-element patterns and far-field radiation patterns are then derived. Some specific examples are given to exhibit the significant reduction in computational effort. It is concluded that this method may be generalized to the analysis of higher order excitation modes and to nonuniform spaced arrays.     

Analysis of yagi-uda-type antennas

A method of analyzing Yagi-Uda-type antennas is presented. Since the Yagi-Uda array is a fairly well-known antenna, it is used as an example to demonstrate the application and accuracy of the method. However, the method of solution is not limited to a planar array, such as the Yagi, but can be applied to arrays of nonplanar linear elements. The approach taken in analyzing Yagi-Uda antennas is based on rigorous equations for the electric field radiated by the elements in the array. All interactions are taken into account. Calculated results are presented for the Yagi-Uda array that show excellent agreement with experimental results reported in the literature. In addition, the dependence of the far-field patterns on the phase velocity is shown. It is also demonstrated that the phase velocity is generally nonuniform along the array.     

The effect of a finite-distance signal source on a far-fieldsteering Applebaum array-two dimensional array case

Approximate expressions are obtained for the output signal-to-noise ratio (SNR) expressed in terms of the finite signal distance and signal direction for a finite-distance signal source's effect on the performance of a far-field steering two-dimensional Applebaum-type adaptive array. The expression is shown to be consistent with the actual simulated value. Using that expression, a simplified rule is obtained to determine the distance between the signal source and the array center at which the output SNR loss is given by a specific value. The SNR value so obtained varied with two-dimensional signal direction. The analysis for the case of an arbitrarily located array is presented, followed by the cases for rectangular, circular and elliptical arrays. It was found that this distance associated with the given SNR value is always less for a rectangular array than that of a linear array when the total number of array elements for both are equal and the performances of an elliptical array are similar to those of a circular array     

A theory of antenna array conformal to surfaces of revolution

For a conformal array of nonparallel radiators the classical array theory fails to offer a convenient way for calculating the array pattern and its cross-polarized counterpart. This study shows that under a wide range of conditions, these patterns can be simply obtained from the array space factor by partial differentiation. The scalar space factor of an array, therefore, can be considered as a generating function for the array patterns for both the principal and the cross-polarized fields in a vector form. To illustrate the theory, arc arrays of uniformly spaced dipoles and slots are treated. The analysis is extended to the case of conical arrays.     

Analysis of finite arrays of axially directed printed dipoles on electrically large circular cylinders

Various arrays consisting of finite number of printed dipoles on electrically large dielectric coated circular cylinders are investigated using a hybrid method of moments/Green's function technique in the spatial domain. This is basically an "element by element" approach in which the mutual coupling between dipoles through space as well as surface waves is incorporated. The efficiency of the method comes from the computation of the Green's function, where three types of spatial domain Green's function representations are used interchangeably, based on their computational efficiency and regions where they remain accurate. Numerical results are presented in the form of array current distributions, active reflection coefficient and far-field pattern to indicate the efficiency and accuracy of the method. Furthermore, these results are compared with similar results obtained from finite arrays of printed dipoles on grounded planar dielectric slabs. It is shown that planar approximations, except for small separations, can not be used due to the mutual coupling between the array elements. Consequently, basic performance metrics of printed dipole arrays on coated cylinders show significant discrepancies when compared to their planar counterparts.     

Aerial arrays with asymmetrical thinning

The use of asymmetrical element spacings in thinned aerial arrays is shown to give symmetrical radiation patterns. The use of asymmetrical element spacings gives lower sidelobe levels than symmetrical spacings. With an array of nine elements in a 19? array, the greatest sidelobe level is reduced from ?5.61 dB to ?6.87 dB by using an asymmetrical array instead of a symmetrical array.     

非对称单脊波导裂缝阵天线分析

将Ｅｌｌｉｏｔｔ关于矩形波导缝阵理论推广运用到非对称单脊波导裂缝阵天线上，在考虑了裂缝外部互耦影响的情况下，给出相应的两个设计方程，同时给出８单元谐振裂缝线阵的具体计算和设计方法。加工样品的近场和远场测试结果证明了本文理论和设计方法是正确有效的。