Approximation techniques for the mutual admittance of slot antennas on metallic cones

The effect of scattering from a sharp tip on mutual admittance is investigated for pairs of circumferential and radial slots on a semi-infinite metallic cone. Mutual coupling measurements as a function frequency and angular separation are presented and compared with numerical calculations. The base of the conical model used in the experimental study was terminated in a spherical cap to minimize scattering from the finite length of the apparatus. The circumferential slot results illustrate interference effects between the direct coupling from slot-to-slot via the geodesic path over the conical surface and the tip back scattering. For the radial slot configuration, the results exhibit negligible tip scattering effects. The analysis utilizes a computer calculation of mutual coupling between circumferential and axial slots on an equivalent cylinder to predict the direct coupling contribution and utilizes the tip diffraction coefficient for calculating the component scattered by the apex. The tip diffraction coefficient is derived from an asymptotic expression for the tip-scattered component of the surface magnetic field excited on a semi-infinite conical surface.     

Transient and time-harmonic dyadic Green's functions for a perfectly conducting cone

New representations for the time-dependent dyadic Green's functions for a perfectly conducting semi-infinite cone are presented. For the special case of small cone angles and an on-axis source, simplified expressions are given for both the time-dependent and time-harmonic regimes.     

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     

Natural and mutual conductances of ring groove in a finite cone

There are researched dependences of real and imaging parts of natural and mutual conductance of ring grooves on their position of finite and semi-infinite ideally conductive cones. It is shown that influence of cone edge on these dependences can be essential and it must be taken into account during calculation of scattering properties of finite conic structures with ring grooves.     

Cone tip scattering: Endfire region

Significant scattering from the tip of a finite cone viewed at rear aspect angles has previously been reported. The observed return from the far end of the target is largest for horizontal polarization at near grazing angles of incidence. The contribution to the tip return arising from direct diffraction is obtained by consideration of scattering from a slender semi-infinite cone. Comparison of these results with experiment then provides information on the effect of traveling-wave contributions to the tip return.     

Radiation from a monopole excited cone

This paper considers radiation from a finite, right circular, perfectly conducting cone which is excited by a quarter-wave monopole protruding from the center of its base. The cone is assumed to be of a size which places it above the resonance region, making a solution by the geometrical theory of diffraction possible. A formula which allows determination of the tip radiated ray from a semi-infinite cone excited by a uniform, in-phase, magnetic ring current is first derived. This is then used in conjunction with certain other known canonical solutions to obtain a complete solution for the proposed excitation. Radiation patterns, computed on a digital machine from the formulas derived, are compared with measured results and good agreement demonstrated.     

Symmetric electromagnetic field of a circular loop antenna over the conductive cone of finite length

The diffraction properties of the field of circular loop antenna over the conic surface of finite length have been investigated. The relationships of the radiated power as a function of the antenna position on the symmetry axis of the cone were established. The directional patterns and field distribution in the near-field zone were obtained for different geometrical parameters of the diffraction system. The results obtained were compared with similar relationships for semi-infinite cones.     

窄缝耦合共振特性分析

应用时域有限差分法模拟了正弦波和电磁脉冲对窄缝的耦合过程，计算了直缝和扭曲缝的耦合穿透功率和能量，通过分析窄缝的耦合传输系数变化曲线，得出窄缝发生耦合共振的条件和规律。并通过直缝与扭曲缝耦合情况的比较，表明了扭曲缝具有较好的电磁防护能力。     

Scattering from finite by infinite arrays of slots in a thinconducting wedge

The radar scattering from a finite by infinite array of slots cut into a thin conducting wedge is considered. The wedge is formed by taking a thin ground plane and applying a bend to create a sharp edge which is parallel to the columns of slots in the infinite axis. Results are derived for thin linear slots whose major axes are either parallel or perpendicular to the edge. A hybrid moment method and geometrical theory of diffraction approach is used, with magnetic current expansion functions defined using Floquet's theorem on single columns of slots. Predictions generally agree with scattering measurements of finite by finite array physical models with monostatic patterns taken in a plane orthogonal to the sharp edge     

The physical optics radar cross section of an elliptic cone

The physical optics approximation is used to evaluate the backseattering radar cross section of a semi-infinite metallic elliptic cone. The resulting formula can be directly interpreted as a generalization Of the well-known formula for the baekscattering cross section of a circular cone. In addition the bistatic radar cross section of the elliptic cone is calculated.     

Numerical evaluation of dyadic diffraction coefficients andbistatic radar cross sections for a perfectly conducting semi-infiniteelliptic cone

In this paper, the scattering of electromagnetic waves by a perfectly conducting semi-infinite elliptic cone is treated. The exact solution of this boundary value problem in problem-adapted spheroconal coordinates in the form of a spherical multipole expansion is of poor convergence if both the source point and the field point are far away from the cone's tip. Therefore, an appropriate sequence transformation of these series expansions (we apply the Shanks transformation) is necessary to numerically determine the dyadic diffraction coefficients and bistatic radar cross sections (RCS) for an arbitrary elliptic cone. Our far-field data for an elliptic cone, a circular cone, and a plane angular sector are compared with some other results obtained with the aid of quite different methods     

含有折线型缝隙金属平板散射分析

分析了有限大金属平板上包含折线形状缝隙时的散射场。缝隙和金属平板的散射分别采用矩量法和物理光学法得到。折线型缝隙由两种不同倾斜方向的直缝组成,然后叠加各段缝隙和金属板的散射场即可得到总场。     

有限元\\边界元混合算法分析波导裂缝阵列天线

研究了一种分析波导裂缝阵列天线的方法。将有限元-边界元混合算法（FE-BI）应用于波导裂缝阵列天线的计算中,建立理论分析模型,计算波导裂缝上的等效磁流,进而求解整个天线阵列的远场辐射特性。为了检验这种方法的正确性,将所得的数值计算结果与测试值进行了比较,结果表明：FE-BI法可以作为计算波导裂缝阵列天线的一种有效的方法。     

基于应力-位移混合有限元法的激光超声数值模拟

为了研究激光辐照各向同性半无限大铝材料内超声波的激发和传播特征,采用理想匹配层和应力-位移混合有限元方法建立了半无限大介质中激光激发超声波的有限元数值模型。模拟研究了各向同性半无限大铝材料内激发产生的瞬态波场图和垂直表面位移,并与相同几何模型下采用有限元方法得到的结果进行了对比分析。结果表明,应力-位移混合有限元方法能够有效地消除模型截断边界处的反射波,精确地模拟出无限大固体材料内激光激发超声波的产生和传播特性。数值模拟结果为进一步研究微纳米薄膜材料中皮秒或飞秒激光激发超声波提供了有效的方法。     

Creeping waves on a perfectly conducting cone

The rigorously formulated scalar and vector Green's functions for a perfectly conducting semi-infinite cone are approximated asymptotically to furnish the high-frequency creeping wave contributions when the source and observation points are both located on the cone surface. The results are expressed in the ray-optical format of the geometrical theory of diffraction and thus provide another canonical solution for verification of the postulates of that theory. The analytical procedure for isolating the creeping waves from other high-frequency phenomena such as tip diffraction is motivated by the methodology for the simpler circular cylinder problem, to which the present solution reduces when the cone-to-cylinder transition is performed. The results are of interest for calculation of source-induced surface currents, and of mutual coupling between slot array elements, on conical surfaces.     

2 X 2 etched slot array with corporate slotline feed network

Measured and simulated results for a planar 2times2 slot array corporately fed by a slotline feed network are presented. The antenna array has a coplanar-waveguide input port and the slots are etched on the finite ground plane of a single substrate. The coplanar-waveguide transmission line is transitioned into a four-way slotline feed network, which directly feeds the four half-wavelength slots from the narrow edges of the slots. An experimental array achieved an impedance bandwidth of more than 12%, stable bidirectional radiation patterns with low cross-polarisation, and a maximum gain of more than 8 dBi.     

Localizing the spatial and temporal electromagnetic fields on theaxis of a lossy cylinder

Given a specified form, both in time and space, for the electromagnetic fields on the axis of a lossy cylinder, the authors determine, analytically, the required azimuthally symmetric source distribution on the surface of the cylinder that generates such internal fields. They then show that this source is equivalent to an array with finite number of cylindrical slots in a metal encasing that are impulsed by specified voltages at a finite sequence of discrete times. A confirming forward calculation exhibits excellent agreement between the specified field form and that generated by the array of cylindrical slots. Potential applications are to hyperthermic cancer therapy, bioelectromagnetics and nondestructive testing     

Electromagnetic scattering by and transmission through athree-dimensional slot in a thick conducting plane

A hybrid numerical technique for a characterization of the scattering and transmission properties of a three-dimensional slot in a thick conducting plane is presented. The technique combines the finite element and boundary integral methods to formulate a system for the solution of the aperture fields and by virtue of the finite element method, it is applicable to inhomogeneously filled slots of arbitrary shape. The numerical implementation is described for the edge-based expansion functions associated with rectangular brick elements, and examples are presented demonstrating the validity, versatility, and capability of the technique. These also provide some understanding of the slots scattering and transmission properties as a function of its geometry and material filling     

The design of large waveguide arrays of shunt slots

It is shown that the method of moments (MM) solution can determine the active admittance of each slot in a finite array and that the infinite array model is quite accurate for the design of large waveguide arrays of shunt slots. Active admittances computed by an infinite array model agree favorably with that of slots in sufficiently large finite arrays. Measured results verify the MM solution, thereby validating the infinite array model accuracy     

New linear-programming-based filter design

It is well known that the filter-design problem with mask constraints can be formulated as a semi-infinite program. There are two approaches toward the solution of this semi-infinite program. The first griding approach relaxes the semi-infinite constraint by refining it in the finite griding domain so it does not always guarantee global optimal and feasible solution. The second semi-definite programming (SDP)-based approach does guarantee the global optimal solution and excellently handles positive real constraints. However, the magnitude constraints are still persistent and not yet handled by SDP tool in an efficient manner. In this brief, a new tight polyhedral approximation for semi-infinite constrained domain is proposed. Based on it, we present a new linear-programming-based solution method for filter design, which unlike the griding approach yields global solution and unlike SDP based approach is practical for even long-tap filters. Simulation results confirm the viability of the proposed method.