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1.
In the complex source point technique, an omnidirectional source diffraction solution becomes that for a directive beam when the coordinates of the source position are given appropriate complex values. This is applied to include feed directivity in reflector edge diffraction. Solutions and numerical examples for planar strip and parabolic cylinder reflectors are given, including an offset parabolic reflector. The main beams of parabolic reflectors are calculated by aperture integration and the edge diffracted fields by uniform diffraction theory. In both cases, a complex source point feed in the near or far field of the reflector may be used in the pattern calculation, with improvements in accuracy in the lateral and spillover pattern lobes 相似文献
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The far field of a two-dimensional beam resulting from an electric line source at a complex position is described, its half-power beamwidth determined, and its validity as an antenna beam indicated. Farfield diffraction by a half-plane is then determined from an exact uniform solution for an isotropic line source by making the source position complex. The same basic solution and technique are used for beam diffraction by a wide slit, with first-order interaction between the slit edges included. Numerical results for normal incidence illustrate the evolution of the diffraction patterns from those for an omnidirectional source to those for a highly directive beam. Results for plane wave incidence by a slit also come out of this solution. The remarkable simplicity and convenience of this method relative to alternative asymptotic procedures is discussed. 相似文献
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The diffraction of an arbitrary cylindrical wave due to a line source and incident on a half-plane is treated by the uniform asymptotic theory of edge diffraction. For large wavenumberk , an asymptotic solution for the total field up to and including terms of orderk^{-3/2} relative to the incident field is derived. This solution is uniformly valid for all observation points, including points near the edge and the shadow boundaries. In particualr, two special cases are considered: A) the line source is located on the half-plane, and radiates anE -polarized wave and B) the line source is located in the aperture complementary to the half-plane and radiates anH -polarized wave. A companion paper will show that our asymptotic solution for Case A) is in complete agreement with the asymptotic expansion of the exact solution. For the same diffraction problem, asymptotic solutions obtained by the method of slope diffraction coefficients and the method of equivalent currents are also discussed. It is found that the latter solutions agree with the exact one only when i) the observation point is away from the edge and the shadow boundaries, and/or ii) the terms of orderk^{-3/2} in the field solution are ignored. 相似文献
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为了研究空心光束通过硬边光阑透镜傍轴ABCD光学系统后的传输特性,利用柯林斯衍射积分公式,推导出了空心高斯光束通过受圆孔硬边光阑限制的傍轴ABCD光学系统的传输公式,所得公式可用来描述空心高斯光束通过任意傍轴ABCD光学系统的传输.研究了光阑、透镜以及光阑透镜系统对空心高斯光束传输特性的影响,并用数值例做了详细说明.结果表明,光阑和透镜均会使光束的光场分布向源平面前移,光阑会破坏空心高斯光束的空心性,而单纯的透镜只改变光场分布,不会破坏光束的空心性.这一结果对于空心光束的产生和应用有理论指导意义. 相似文献
5.
Gaussian beams are used as basis elements in field representations. To gain insight into how the choice of beam parameters affects the final representation, a systematic study for the simple test case of a one-dimensional linearly phased cosine-aperture distribution has been undertaken. By successively adding individual displaced and/or tilted beams with large, narrow, or matched waists, one can assess how the elements in various portions of the lattice contribute to the build-up of the actual field in the aperture, near zone, and far zone. Adding enough beams always guarantees homing in on the exact solution, as is verified here by independent comparison. Different beam choices imply different modeling of the radiation process. The understanding gained thereby is helpful for selecting beam parameters in subsequent applications where it is necessary to balance requirements of good convergence, ease of computation, and ability to track the beams through perturbing environments like a radome. Indications are that the narrow beams provide the most robust and versatile formulation to deal with these generalized conditions 相似文献
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A previously developed Gabor-based quasi-ray narrow-waisted (NW) Gaussian beam (GB) algorithm for time-harmonic propagation of aperture-excited two-dimensional (2-D) electromagnetic fields through a planar dielectric layer is extended here to the time domain (TD) to deal with short-pulse excitation. The dielectric layer is assumed to be nondispersive; however, slight Ohmic losses can be accommodated. The frequency domain (FD) algorithm is based on a self-consistent discretization of the aperture field distribution in terms of basis NW-GBs in conjunction with an efficient quasireal ray tracing scheme for tracking the individual basis beams. The TD results are obtained by analytic Fourier inversion from the FD in terms of pulsed beam wavepackets, following a procedure similar to that utilized by Galdi et al. (see IEEE Trans. Antennas Propagat., vol.49, p.1322-32, Sept. 2001) in connection with free-space aperture radiation. The proposed algorithm is validated and calibrated against a rigorous numerical reference solution via an extensive series of numerical experiments. A priori accuracy assessments in terms of critical nondimensional estimators, and computational costs, are also given attention. 相似文献
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The corrugated horn has been established as an antenna with low sidelobes and backlobes, rotationally symmetric patterns (for square pyramidal and conical horn shapes), and broad-band performance [1]-[9]. These properties make this horn useful for many applications. Previous studies have used conventional aperture integration techniques to evaluate the patterns of the corrugated horn. In general, the near axisE -plane radiation pattern of a pyramidal corrugated horn may be adequately predicted from standard analysis established for theH -plane patterns of conventional horn geometries [3]. This method, however, fails to predict the far-out sidelobe and backlobe radiation levels. The work presented here uses a knowledge of the aperture fields to predict the pattern using aperture integration and diffraction theory. The assumptions made concerning the aperture fields were verified by probing the internal fields and aperture fields of anX band corrugated horn. The results of this field probing are contained in the Appendix. The method of solution used in this paper parallels that used in previous publications [10]-[12]. Specifically, the pattern in the main beam region is computed using conventional aperture integration procedures, the contribution of theH -plane edges is found using a slope diffraction analysis, and the contribution of theE -plane edges is found by use of duality. 相似文献
13.
Gimeno B. Diez A. Navasquillo J. Pomer F. 《Antennas and Propagation, IEEE Transactions on》1995,43(3):317-322
An hybrid angular spectrum method-Galerkin moment procedure has been developed to analyze the diffraction of an electromagnetic beam incident obliquely on an infinite planar periodic metal-strip grating. The integral expression obtained for the scattered field is expanded by means of an asymptotic method for determining the diffracted far-field. Some numerical examples show the decomposition of the incident beam in several beams corresponding to the propagating Floquet harmonics excited in the grating. The propagation directions of these beams show deviations with respect to the directions predicted by the Floquet theorem. The profile of the scattered far-field is analyzed as a function of the geometrical and electrical parameters 相似文献
14.
A comparison among 1-, 3-, and 7-horn feeds for a 37-beam MBA 总被引:2,自引:0,他引:2
A very common multiple beam antenna (MBA) configuration consists of a collimating device illuminated by an array of feeds. The collimating device is usually a reflector or a lens. The feeds are usually horn antennas with a circular aperture. The reflector is usually offset-fed to eliminate aperture blockage; the lens is center fed. The antenna's feeds are excited to produce a finite number of beams, so as to provide contiguous coverage of the field of view. The designer is forced to minimize the angular spacing between adjacent beams in order to maximize the minimum gain over the antenna's field of view. On the other hand, the feed horn's aperture gain is maximized when the feed horn spacing and its aperture diameter are equal. This results in antenna efficiency of the order of 30% when a single feed horn is excited to produce a beam. When a cluster of 3 or 7 adjacent feed horns are excited to produce a single beam, antenna efficiency can be increased to 50%. When it is tolerable, several identical antenna apertures can be used to replace a single aperture configuration. In this case, each of M apertures produces approximately N/M beams of an MBA that produces N beams. Horns producing adjacent beams do not illuminate the same aperture. This permits the use of a much larger horn aperture for a given beam spacing. This results in reduced spillover, higher gain of each beam, and increased antenna efficiency of each aperture. This paper investigates the maximization of gain for several lens antennas. It shows that antenna gain is increased as its focal length is decreased. That is, a focal length-to-diameter ratio (F/D) less than 1 is preferred 相似文献
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带有螺旋相位分布的波束都具有轨道角动量(Orbital Angular Momentum,OAM),其螺旋相位取决于OAM态拓扑荷数。理论分析了叠加涡旋光束的相位及光场分布,然后将叠加态涡旋光束的相位分布图加载到空间光调制器上产生了多态涡旋光束,讨论了不同拓扑荷数叠加时光场衍射图的分布情况。实验结果表明,叠加态的涡旋光束光场衍射图随着叠加光束拓扑荷数的正负以及数值而呈一定规律性变化,即当叠加的两束光拓扑荷数为异号时,衍射产生的光斑数为两束光拓扑荷数绝对值之和;当叠加的两束光拓扑荷数为同号时,衍射产生的光斑数为两束光拓扑荷数之差的绝对值。通过此性质可以检验涡旋光束的拓扑荷数,为叠加涡旋光束在自由空间光复用通信系统的拓扑荷数检测提供了新的方法。 相似文献
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涡旋光场调控对涡旋光在激光通信、生物操控等领域的应用研究具有重要意义。为了揭示透镜球差对拉盖尔-高斯(Laguerre-Gaussian,LG)涡旋光束传输特性的影响,本文基于菲涅尔衍射理论,模拟研究了不同透镜球差系数下的LG光束聚焦场的强度、相位以及螺旋谱分布。结果表明:光学系统初级球差系数的增大恶化了LG光束聚焦场的强度分布和螺旋相位,弥散了轨道角动量(orbital angular momentum,OAM) 。由此,本文提出了一种光阑补偿方案,通过在透镜前添加大小合适的圆孔光阑,以消除透镜像差。光阑补偿后的LG光束聚焦场由星芒状空心分布恢复为空心圆环分布,OAM态保持单一稳定。本研究工作为改善透镜像差对涡旋光的传输影响提供了解决方案。 相似文献
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In this communication a note on the coupling efficiency between an antenna and a Gaussian beam is presented. The calculations of the coupling efficiency from both methods, a nomorlized inner product between the antenna radiation pattern and the Gaussian-beam pattern or alternatively, between the electric field at the antenna aperture and a two-dimensional field representation of a Gaussian beam, are compared for different aperture size in wavelength. How a correct solution can be gotten is stated. 相似文献
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Anomalous diffraction of light in liquid upon the ultrasonic coagulation of suspended microparticles
A. V. Gerus T. G. Gerus A. L. Filatov 《Journal of Communications Technology and Electronics》2012,57(8):853-856
Anomalous diffraction by the periodic filamentary structure that consists of coagulated heavy particles in water is experimentally studied under the conditions for the standing acoustic wave in cavity. The diffraction is sensitive to both the conventional photoelastic effect and the filamentary structure. The width of the narrow beams that are formed in the near-field diffraction zone is several times less than the aperture of the incident beam, and the narrow beams propagate in space with the same angular divergence as the incident broad beam does. 相似文献
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Shlivinski A. Heyman E. Boag A. Letrou C. 《Antennas and Propagation, IEEE Transactions on》2004,52(8):2042-2056
A new discrete phase space Gaussian beam (GB) summation representation for ultrawide-band (UWB) radiation from an aperture source distribution is presented. The formulation is based on the theory of the windowed Fourier transform (WFT) frames, wherein we introduce a novel relation between the frequency and the frame overcompleteness. With this procedure, the discrete lattice of beams that are emitted by the aperture satisfies the main requirement of being frequency independent, so that only a single set of beams needs to be traced through the medium for all the frequencies in the band. It is also shown that a properly tuned class of iso-diffracting (ID) Gaussian-windows provides the "snuggest" frame representation for all frequencies, thus generating stable and localized expansion coefficients. Furthermore, due to the ID property, the resulting GBs propagators are fully described by frequency independent matrices whose calculation in the ambient environment need to be done only once for all frequencies. Consequently, the theory may also be expressed directly in the time-domain as will be presented elsewhere. The localization implied by the new formulation is demonstrated numerically for an UWB focused aperture. It is shown that the algorithm extracts the local radiation properties of the aperture source and enhances only those beams that conform with these properties, i.e., those residing near the phase space Lagrange manifold. Further localization is due to the fact the algorithm accounts only for beams that pass within a few beamwidths vicinity of the observation point. It is thus shown that the total number of beams is much smaller than the Landau Pollak bound on the aperture's degrees of freedom. 相似文献
20.
Burkholder R.J. Pathak P.H. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1991,79(10):1401-1412
Gaussian beam (GB) representation methods are used to analyze the electromagnetic coupling into and the scattering by a large nonuniform cavity. The aperture field in the cavity is decomposed into beams using the Gabor expansion, and shooting techniques are then employed. The method is illustrated only for the two-dimensional (2-D) case. The GBs are tracked axially using the rules of beam optics which ignore any beam distortion upon reflection at the walls. The effects of beam distortion are not significant for relatively slowly varying waveguide cavities. The field scattered into the exterior by the termination within the cavity is found using a reciprocity integral formulation which requires a knowledge of the beam fields near the termination. Numerical results based on this GB approach are presented and compared with results based on an independent reference solution 相似文献