Propagation and radiation characteristics of low-permittivity dielectric cones

An approximate theory is proposed to explain the propagation and radiation characteristics of low-permittivity conical dielectric waveguides of narrow flare angle. Theoretical radiation patterns are predicted and compared with those obtained for corrugated conical horns. The considerable similarity which is predicted is supported by experimental results obtained at 9 GHz using cones made from expanded polystyrene.     

Crosspolarised radiation from waveguides and narrow-angle horns

Radiation from circular waveguides and narrow-angle cones is obtained numerically and their crosspolarised radiation is presented. It is found that the peak crosspolarised radiation is generally a sensitive function of wall thickness, aperture diameter and overall length of the waveguide.     

An experimental study of simulated plasma-covered slots on cylinders and cones

The effect of a plasma on the radiation characteristics of slot and gap apertures located on cylinders and cones has been studied by means of a plasma simulation technique. The relative index of refraction of less than unity between the plasma and free space was maintained for the model by an analog tank in which free space was represented by a high dielectric constant liquid and plasma by a lower dielectric material. The antenna pattern of an axial slot on a cylinder with a simulated plasma covering had good agreement with theory for radiation in the equatorial plane, as did the antenna pattern for a simulated plasma-covered, center-fed, cylindrical antenna. The experimental pattern of a cavity-fed circumferential slot on a cone-hemisphere covered with simulated plasma is also presented.     

Plane wave diffraction from a small half-sphere mounted on a large conducting body

Using image theory and the scattering solution for a sphere, the plane wave scattering by a small, perfectly conducting half-sphere on a conducting plane is obtained first. The scattered field can then be identified as that radiated from a combination of electric and magnetic dipoles on the plane. Equating these dipole fields to the corresponding radiation dipoles, we can solve for the induced scattering dipole moments. These moments can now be used to obtain the scattering of a small half-sphere mounted, for example, on large cones spheres, cylinders etc., provided the simpler problem of radiation dipoles on the large bodies has been solved first.     

一种应用于基站天线的新型球透镜

针对传统龙伯透镜结构复杂、制作工艺难度大、不易实现批量化生产等问题,提出了一种应用于基站天线的新型球透镜,采用同一种介质材料的一个介质基座和多个介质锥体,再将各介质锥体均匀分布连接于介质基座上,组成球透镜.仿真结果表明:采用所提出的球透镜的双极化基站天线,具有良好的辐射方向图和高增益性能.     

A UTD type analysis of the plane wave scattering by a fullyilluminated perfectly conducting cone

A uniform high-frequency asymptotic solution, based on the physical optics (PO) approximation, is obtained in the format of the uniform geometrical theory of diffraction (UTD) to describe the fields diffracted by the tip of a semi-infinite, perfectly conducting cone when it is fully illuminated by an electromagnetic plane wave. The solution is expressed in terms of an integral, over finite limits which can be integrated numerically without difficulty. The results computed from the uniform asymptotic PO solution compare well with previously published results given for narrow-angle semi-infinite cones. In addition, they compare well with measurement and with an independent moment method (MM) solution for the scattering by a finite flat-backed cone in which several higher order wave interactions are found to be significant; one such interaction is between the tip and the base of the cone. Expressions are provided which are useful for calculating this tip-base interaction and confirm its relative importance. These expressions also provide tip diffraction effects which are important within the forward paraxial zone for the radiation by antennas on cones     

Symmetric electromagnetic excitation of a finite conducting cone with azimuthal slot

Diffraction properties of finite conducting cone, excited by azimuthal slot, are investigated. Dependencies of radiated power on the slot position on the cone’s surface are obtained. Field radiation patterns for various geometric parameters of diffraction system and field distribution in the near region are presented. The results obtained for finite cones are compared to those of semi-finite ones.     

Biconical antennas with unequal cone angles

The problem of radiation and reception of electromagnetic waves associated with a spherically capped biconical antenna having unequal cone angles ψ₁ and ψ₂ is investigated. Both cones that comprise a bicone are excited symmetrically at the apices by a voltage source so that the only higher order modes are TM. A variational expression for the terminal admittance is derived. Under the wide-angle approximation, expressions for the radiated field, the effective height, and the terminal admittance are obtained. In addition, limiting values of these quantities are derived for electrically small and electrically large wide-angle bicones. The results for arbitrary cone angles are new and subsume results that appear in the existing literature as special cases such as where ψ₁=ψ₂ or ψ₂=π/2. Moreover, the approximations of this paper are more accurate than many in the literature. It is argued that the radiation pattern of an electrically small cone is proportional to sin &thetas;, which is similar to that of a short dipole; whereas the pattern behaves like 1/sin &thetas; for electrically large cones. The parameter &thetas; is the angle from the bicone's axis of symmetry to the observation direction. Consequently, the direction of maximum radiation changes with exciting frequency for a bicone of fixed length. Although most of the analyses are presented in the frequency-domain, time-domain responses of bicones are discussed for some special cases that are similar to situations considered by Harrison and Williams. In particular, the time-domain radiated field and the received voltage are shown to depend on the input's passband and on the match between the source and the bicone     

Electromagnetic scattering from finite circular and elliptic cones

A formulation based on the physical theory of diffraction (PTD) is presented for finite conical surfaces with circular and elliptic cross sections. The base-rim discontinuity is represented by equivalent currents, including second-order terms extended for elliptic boundaries. Tip-rim interactions are examined as a function of the tip-rim distance, cone angle, and illumination angle for circular cones; and their implication for elliptic cones is noted. The diffraction contribution from tip-rim interactions is shown to be dependent on the cone angle and the illumination angle but to be relatively insensitive to the tip-rim distance. The Fock Ansatz is used to enlarge the validity of the PTD formulation to cases where nonspecular effects arising from surface curvature and shadow boundaries are significant. The formulation is applied to cones with varying ellipticity for axial and oblique illumination. Correlation is made with published results for circular cones and with experimental data for an elliptic cone.     

Bistability in the radiation pressure on two-level atoms in a ringcavity

A simple model for the interaction of a beam of two-level atoms with a running radiation model in a ring cavity is formulated. The occurrence of optical bistability significantly affects the radiation pressure force on atoms. Hysteresis effects are predicted for the transverse component of atomic velocity which couples with the electric field     

光纤陀螺光学器件的空间辐射效应及防护技术

针对光纤陀螺用光学器件在空间辐射环境下受电离损伤和位移损伤影响性能下降的问题,分别分析了光纤、SLD光源、PIN-FET探测器的空间辐射效应。为保证光纤陀螺在空间的工作性能,从被动屏蔽和主动加固两方面讨论了光学器件的辐射防护技术。考虑到不同光学器件对不同类型辐射损伤的敏感性以及航天器载荷对重量的严格要求,从电离损伤屏蔽和位移损伤屏蔽两方面对屏蔽厚度进行了优化设计。通过对各光学器件辐射效应机理的分析,讨论了提高光学器件本身抗辐射能力的主动加固技术。     

基于Fluent的飞行器流场建模与红外辐射特性分析

以某型战斗机为研究对象,通过三维建模与网格划分过程建立飞机的流场计算模型,基于商用CFD软件ANSYS Fluent 16.0对飞机的外流场特性进行数值模拟。计算中利用太阳射线追踪算法综合考虑了太阳辐射对机身温度场的影响,采用离散坐标法（DO辐射模型）对辐射传输方程进行耦合迭代计算,利用不带化学反应的组分输运模型（Species Transport Model）模拟燃烧后高温尾焰喷射过程,获得了飞机外流场的温度、浓度及尾流组分分布数据。简要分析了太阳辐射对温度场变化的影响,飞行马赫数对流场红外辐射的影响以及尾焰流场分布情况。分析表明:太阳辐射对蒙皮加热较小,最高升温效果仅为5 K左右,随马赫数的增加飞行器机身背部与腹部红外辐射强度差异明显,最高时腹部辐射强度为机身最大辐射强度2倍左右,激波作用下尾焰后方会出现最高450 K和580 K两个间断的核心高温区域,尾焰红外辐射强度分布符合梨形特征分布趋势。     

扬声器新动态

介绍了近年来国外不用纸锥盆作声辐射零件的金属盆,铍、铝、镁、钛等几种轻金属特性。以及金属氧化后（陶瓷化）的材料特性。还介绍了轻金属合金及供锥盆使用的工程纤维特性。最后介绍一种无磁芯、无导磁夹板的钕铁硼新磁路,并进行了FEMM 1 in芯模拟,显示其B值可达1.3T。这是一种失真甚小的Hi—Fi用磁路,可供有条件的音响发烧友参考。     

Numerical calculation of the diffraction coefficients for anarbitrary shaped perfectly conducting cone

A method for numerical calculation of the diffraction coefficients for electromagnetic diffraction by arbitrarily shaped perfectly conducting cones is proposed. The approach makes an extensive use of the analytic formulas of Smyshlyaev [1993] in combination with further developments, including a use of the potential theory adapted to the Laplace-Beltrami operator on a subdomain of unit sphere. This reduces the problem to a Fredholm integral equation on the closed curve of the unit sphere (defining the cone's geometry) which can be solved numerically. This strategy permits us to implement a numerical code for calculation of the diffraction coefficients for cones of rather general cross sections. Results of sample calculations for the circular and elliptic cones are given     

Electromagnetic Excitation of PEC Slotted Cones by Elementary Radial Dipoles—A Semi-Inversion Analysis

A novel method is presented that is based on the use of the Kontorovich–Lebedev integral transform and the semi-inversion technique, developed for building the efficient and accurate numerical solutions to the boundary-value problems of electromagnetic wave scattering by the 3D coaxial slotted cones. A generic structure under consideration consists of two semi-infinite coaxial circular perfectly electrical conducting and zero-thickness cones with periodic longitudinal slots excited by a radial dipole. The considered problem is reduced to an infinite set of linear algebraic equations of the Fredholm second kind that is truncated and solved numerically. A detail analysis of the accuracy and convergence of the method is presented. The basic electromagnetic characteristics such as the field behavior near the structure singularities, field patterns in the wave zone, and field polarization for various problem parameters are investigated for the cones excited by on-axis elementary dipoles. The slotted cones allow obtaining more directional patterns in wider band than the solid ones.      

The properties of antennas in plasmas

The last five years have witnessed remarkable progress in the theory and measurement of both the radiation and impedance properties of antennas in plasmas. Increased motivation for research in this area has been provided by the Space Shuttle program and by the prospect of nuclear fusion. The focus of attention has been on resonance cones in linear, anisotropic plasmas, including radiation patterns, wave interference, pulse propagation, reflections from boundaries and inhomogeneous media effects. Under nonlinear conditions, the focussed field of a resonance cone can significantly depress the plasma density. Under both linear and nonlinear conditions, the input impedance of dipole and loop antennas has been studied extensively, for both anisotropic and isotropic plasmas. A continuing challenge has been the as-yet-not-fully-explained experimental observation of linear, non-collisional enhanced resistivity of the sheath region around an antenna. Numerical impedance calculations employing simplified velocity distributions have shown particular promise. Ion and electron wave radiation patterns for various antenna shapes have been calculated and checked experimentally. The response of both single antennas and pairs of antennas to plasma fluctuations has been studied and found to have applications to plasma diagnostics.     

集成天线的多通道瓦片式T/R组件测试

雷达T/R组件的集成度越来越高,已出现了将天线也集成在组件上的多通道瓦片式收发T/R组件。由于天线的集成,传统的传导测试方法无法对这种新结构T/R组件的电路性能进行直接测量。针对该问题,提出一种辐射对比测试方法,采用辐射法先对T/R组件天线单元进行测试,然后对集成天线的T/R组件进行测试,最后将天线对T/R组件电路性能的影响扣除,得到T/R组件电路的各项性能参数。在分析测试原理的基础上,对一种集成天线的多通道X波段的瓦片式T/R组件发射峰值功率、通道间相位一致性和接收增益等指标进行了试验测试,测试结果与电路直接测试对比,幅度误差<0.69 dB,相位误差<10.5°,满足工程应用需求。     

Harmonic and Intermodulation Performance of the Semiconductor Bolometer

A mathematical model for the temperature dependence of the bolometer semiconductor resistance is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the harmonic and intermodulation performance of the acquired interferogram voltage with large-amplitude multisinusoidal variations in the incident radiation. The special case of two-tone equal-amplitude incident radiation is considered in detail. The results show that the intermodulation components are always higher than the harmonic components of the same order. The results also show that the second-order intermodulation is always dominant and is higher than the second-harmonic component by about 6 dB. Moreover, the results show that for relatively small incident amplitudes of the incident radiation the ratio between the second- and third-harmonic components is almost equal to the ratio between the second-harmonic component and the fundamental. The results also show that the ratio between the amplitudes of the second- and third-order intermodulation components is almost equal to the ratio between the amplitudes of the second-order intermodulation component and the fundamental.     

Honeycomb wire antenna

A honeycomb wire antenna is numerically analysed. The radiation in the direction normal to the antenna plane is linearly polarised with a low cross-polarisation component of <-30 dB. The gain is dependent on the interior angles of the radiation cell. The maximum gain for a honey comb antenna of two cells by 17 cells with interior angles of 70° is ~20.5 dB, and the gain drop over a 4% frequency bandwidth is ~2.56 dB