Scanning of cosecant beams generated by a tilted planar array ofnonisotropic radiators

A method of scanning a one-dimensional shaped pattern generated by a tilted circular planar array of nonisotropic elements is presented. A method of synthesis of phase function for a desired cosecant pattern and specified amplitude distribution for excitation of the elements of the array is presented. The phase distribution required in the perpendicular direction for retaining the beam shape in the scanned plane is determined. Computed results on the phase distribution and radiation pattern are presented. The appropriate correction is applied to get a better agreement between the realized and desired patterns in this scanned position of the beam     

Generation of cosecant beams from circular arrays

The generation of shaped beams from circular aperture is reported by Chakraborty et al. However there is no data available on the shaped beams from circular arrays. As the circular arrays exist in practice, they are designed to produce shaped beams. A new amplitude distribution is proposed and the concept of energy relations and stationary phase are used to design the optimized phase distribution. Introducing the phase function so obtained the patterns are realized and compared with those of specified. The cosecant beams are generated from small and large circular arrays.     

椭圆对称奇异空心光束通过硬边光阑的传输特性

通过将圆孔光阑函数展开为有限复高斯函数和的方法,利用惠更斯-菲涅耳衍射积分推导出了椭圆对称奇异空心光束通过具有圆孔光阑的近轴ABCD光学系统的传输近似解析公式,并对椭圆对称奇异空心光束在自由空间中通过不同孔径下的硬边光阑的传输特性进行了数值模拟研究。结果表明:自由空间中的近轴光学系统无论在近场还是远场,椭圆对称奇异空心光束的衍射光强分布都与光阑大小有很大的关系。该研究方法对椭圆对称奇异空心光束通过具有圆孔光阑的传输和变换的研究非常有益。     

Diffraction by a circular aperture in a unidirectionally conducting screen

The diffraction of a normally incident plane electromagnetic wave with wave numberkby a circular aperture of radiusain a unidirectionally conducting plane screen of zero thickness and infinite extent is considered. In the limit of largeka, the ratio of the transmission cross section to the geometrical optics valuepi a^{2}, is found up to the order(ka)^{-3/2}.     

Excitation of a circular loop through a small aperture

The problem of determining the current excited on a circular loop which is placed opposite a small circular aperture in a conducting screen, on which an electromagnetic plane wave is incident, is considered. It is shown that this geometry is unusual in that the resulting integrodifferential equation can be reduced to an explicit expression for the current. The total rate of electromagnetic energy flow in the radiation zone is also calculated, as is the angular dependence of the energy flux. Sample results are presented which demonstrate the resonant behavior of the system when the wavelength of the incident wave is equal to the loop circumference.     

Gain-area product of circular aperture

Tables of the gain-area product of a circular aperture are given and explained. Particular attention is given to the realization of maximum gain over a given area with no constraints on aperture size, but with a simple in-phase aperture distribution; and with a given aperture size, using the same class of illumination function     

Generation of multiple simultaneous beams by aperture phase control

Radiation patterns containing multiple beams may be generated by manipulating merely the phase on an aperture, leaving the amplitude distribution undisturbed. The relative phases between the various beams may be adjusted for a best approximation.     

Radiation of an aperture antenna covered by a spherical-shellchiral radome and fed by a circular waveguide

This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TE₁₁ mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically     

Compact circular sector and annular sector dielectric resonatorantennas

We investigate circular sector and annular sector dielectric resonator antenna (DRA) geometries. The advantage these geometries offer, compared to conventional circular cylindrical DRAs are significant reductions in volume, making them potential candidates for use in compact applications such as mobile communication handsets. Approximate theory, simulation, and experimental results are provided to support the findings. In particular, a sector DRA is demonstrated to have 75% less volume than a conventional cylindrical DRA, with the same resonant frequency. The DRA volume minimization for compact antenna design is also discussed and a design is proposed and tested for a mobile telephone handset suitable for the DCS1800 system     

Theoretical and numerical treatment of diffraction through a circular aperture

The three-dimensional diffraction of a scalar plane wave through a circular aperture in an infinite plane screen is analyzed and numerically computed for the case of normal incidence. A modified Babinet's principle is formulated, and this is used to find the diffraction of sound by an acoustically soft circular disk. The spheroidal wave functions are described and applied to the diffraction theory. Numerical values of the rigorous diffraction functions are computed, and these are compared to the approximation obtained by the Huygen-Kirchhoff formulation.     

Surface currents and RCS of a spherical shell with a circular aperture

The electromagnetic scattering behavior of a perfectly conducting, infinitesimally thin, spherical shell with a circular aperture is studied. A time-harmonic plane wave is symmetrically incident upon the aperture. The problem is formulated in terms of theE-field integral equation. This produces two coupled integral equations for the tangential components of the currents on the scatterer surface. The equations are cast into matrix form by application of the method of moments, and expressions for the matrix elements are derived. Calculated values of the surface currents and radar cross sections, not previously available in the open literature, are presented and discussed for several cases of interest.     

Electrostatic potential through a circular aperture in a thickconducting plane

The Hankel transform is applied to express the scattered potential in the spectral domain and the boundary conditions are enforced to obtain simultaneous equations for the transmitted potential inside the thick conducting plane. The simultaneous equations are solved to represent the transmitted and scattered potentials in series forms. Numerical computations are performed to illustrate the behavior of polarizability in terms of the aperture size. The numerical comparisons to other available data show excellent agreement. The presented series solution is fast convergent so that it is very efficient for numerical computation     

Properties of electromagnetic beams generated by ultra-widebandwidth pulse-driven arrays

Analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array are derived and supported with numerical calculations. These bounds extend the meaning of near-field distances or diffraction lengths to the situation where the array driving functions can be broad-bandwidth signals. Particular attention is given to transmitting and receiving array systems which consist of elements that are not large in comparison to the shortest wavelength of significance contained in the signals driving them. Their output signals constitute higher-order beams whose coherence properties are degraded more slowly by diffraction than lower-order beams. It is shown that for certain measures of performance involving these beam characteristics, a localized wave pulse-driven array can outperform similar continuous-wave-driven arrays. An array with independent addressable elements is required to realize these localized wave effects. The enhanced localization effects are intimately coupled to the proper spatial distribution of broad-bandwidth signals driving the array     

圆孔衍射成像的光子学诠释

用量子力学中关于光的粒子性观点,采用概率波对圆孔衍射成像过程进行了讨论。所得到的结论与采用光的波动性观点的惠更斯一菲涅耳原理及Fourier变换方法相同。通过分析,使我们进一步加深了对光的粒子性层面的认识。     

Estimation of wave fields of incident beams in a transmission electron microscope by using a small selected-area aperture

The direction of an electron beam in a nanometer-sized area is measured directly by utilizing a selected-area aperture. By the measurements at several areas in a beam, the wavefront curvature and thus the defocus value of the beam are detected. From the defocus value, the wave field at the specimen plane is also reproduced in consideration of the influences of the condenser aperture and spherical aberration of the illumination lens. The result shows that phase deviation of 2π is caused only at about 10?nm apart from the beam center in a beam with a typical diameter for high-resolution transmission electron microscopy. Based on the defocus value, the convergence angle of the beam is also estimated to be about 6?mrad without being influenced by the partial coherence, that is, independently of the type of the electron gun. Measuring the defocus values for only two beam diameters enables us to determine geometrical parameters peculiar to the illumination system, based on which wave fields of any beam diameters by any condenser aperture sizes can be estimated. The technique proposed in this paper is effective in evaluating the influence of wavefront curvature of incident beams on various kinds of precise measurements conducted in transmission electron microscopes.     

Magnetostatic potential distribution through a circular aperture ina thick conducting plane

The magnetostatic potential distribution through a circular aperture in a thick conducting plane is studied. The Hankel transform and mode-matching technique are utilized to obtain simultaneous equations for the modal coefficients inside the thick conducting plane. The simultaneous equations are solved to illustrate the behavior of the susceptibility in terms of the aperture size. Our solution is numerically very efficient in that it is represented in a rapidly converging series form     

Optimal scale factors for Gaussian field expansions for a circular aperture

Gaussian field expansions for circular aperture antennas are reviewed, and a method for finding optimal scales in these expansions is given, paralleling the method for rectangular antennas presented in an earlier paper. This procedure is shown to lead to approximations structured in the sense that the number of lobes in the approximation corresponds to the number of terms retained in the expansion. An example is given of the development of a cosine distribution from the aperture, through the Fresnel region, to the far field.     

Coupling of power from a circular confocal laser with an output aperture

An iteration technique is used for a theoretical study of the field distributions and diffraction losses at the reflectors of an asymmetric confocal cylindrical resonator having an output hole in one mirror for the low-loss TEM00and TEM10modes with Fresnel numbers ofN = 0.8and 1.2. A digital computer is used to numerically iterate an initially launched uniform distribution as it reflects back and forth between the mirrors until a steady-state field distribution occurs. The edge and coupling hole diffraction losses and the power coupled from an output hole in one mirror are also computed. The presence of the coupling hole produces a perturbation of the field distribution with distortion of the field increasing for increasing Fresnel number and for low-order modes. The relationship between hole radius and power output is presented. An optimum-size coupling hole may be selected from this data, which will yield maximum power output in the mode of operation desired. It has been found that, with the use of a coupling hole, mode selection of the lowest order TEM00mode is possible for resonators having large Fresnel numbers (N > 1.0).     

超高斯光束经椭圆环光阑的衍射和光束质量评价

本文采用数值计算方法讨论了超高斯光束经椭圆环的的衍射现象。以桶中功率（PIB）、β参数和η参数为远场激光光束质量的评价参数,对超高斯光束经椭圆环光阑后的光束质量作了详细的研究,大量数值计算和物理分析表明,在椭圆环外径一定的条件下,超高斯光束经椭圆环衍射后的光束质量与椭圆环的遮拦比和超高斯光束的阶数有关。