Scattering from finite extent frequency selective surfaces illuminated by arbitrary sources

A method is proposed for the computation of the field scattered from a dichroic plate placed in the near-field region of the feeds. The primary pattern of the feed and dichroic plate assembly has been computed.     

Reconfigurable MEMS-enabled frequency selective surfaces

A technique for designing reconfigurable frequency selective surfaces using microelectromechanical systems (MEMS) technology is presented. A method of moments simulation technique for analysing these periodic structures has been used to predict the tunability using this technique. Fabricated and measured results verify the concept of tunability.     

Inkjet printing of frequency selective surfaces

As a step towards low-cost manufacture of conducting arrays for frequency selective surfaces an inkjet procedure is under development. The plane wave transmission response of a printed array compares well with its conventionally etched counterpart and the predictions of modelling software.     

Loss-bandwidth product for frequency selective surfaces

Measurements of the transmission/frequency responses of slot arrays embedded centrally in dielectric layers of various thicknesses show an inverse relationship between the 6 dB width of the transmission band and passband loss. For epsilon /sub r/=4.6, tan delta =0.02 the losses exceed 1 dB for bandwidths below about 25%. A computer model identifies absorption in the dielectric as the main source of the loss.<>     

A spectral-iteration approach for analyzing scattering from frequency selective surfaces

A novel technique, called the spectral-iteration approach, for analyzing the problem of scattering from periodically perforated screens which find useful applications as radomes, optical filters, artificial dielectrics, and so on is applied. The formulation is carried out in the spectral domain where a set of algebraic equations is obtained directly for the spectral coefficients of the aperture field distribution (or the induced current density) rather than via an integral equation formulation. These equations are then solved simultaneously using an iterative procedure developed in this paper that circumvents the need for matrix inversion. Because the matrix solution is avoided in the spectral approach, it is capable of handling large aperture sizes in a computationally efficient manner. The efficiency of computation results from the use of the fast Fourier transform (FFT) algorithm which is employed in the derivation of the algebraic equations and in the iteration procedure. A unique feature of the spectral-iteration approach is that it has a built-in boundary-condition check which provides a reliable indication of the accuracy of the solution. It is also shown that the spectral domain technique can be applied to even a wider class of geometries, e.g., the step discontinuity in a waveguide.     

Frequency selective absorption using lumped element frequency selective surfaces

A three-layer frequency selective surface (FSS) filter is presented that over a narrow frequency band simultaneously attenuates the microwave signal transmitted through and reflected from the filter. This is achieved using a lumped element resistive FSS in between a conventional FSS and a lumped element capacitive FSS. The device is simulated and its functionality is experimentally confirmed using a waveguide setup. More than 30 dB attenuation is observed in both the reflected and transmitted power.     

New method for the efficient summation of double infinite series arising from the spectral domain analysis of frequency selective surfaces

When the method of moments (MoM) in the spectral domain is applied to the analysis of frequency selective surfaces, the entries of the MoM matrix are slowly convergent double infinite series. In this paper, a two-step acceleration technique is developed which makes it possible the fast and accurate computation of these double series in the particular case where subsectional rooftops are used as basis functions. The technique is based on a combination of the use of Kummer's transformation, the use of Poisson's transformation, and the determination of judicious Chebyshev polynomial interpolations of some of the spectral discrete functions involved in the infinite series. The results obtained show that when all the double series of the MoM matrix are to be computed with an accuracy of three significant figures, the new acceleration technique turns out to be about one thousand times faster than brute-force computation, and a few times faster than the acceleration technique based on fast Fourier transform.     

Rings as elements for frequency selective surfaces

Arrays of simple rings on close packed square or triangular lattices are useful frequency selective surfaces for reflector antennas. Reflection bandwidths of about 26 per cent and transmission/reflection band ratios of 3:1 are readily attainable for angles of incidence of up to 45° at least. Experimental transmission coefficients are compared with the results of modal computations.     

有限周期频率选择面的电磁特性分析

从工程测量技术出发提出了一种有限尺寸频率选择表面反射系数和透射系数的数值计算方式,同时使用矩量法及多层快速多极子方法进行了数值仿真.仿真结果表明这一计算方式是可行并可靠的.     

Arrays of concentric rings as frequency selective surfaces

Concentric rings can be used as array elements in frequency selective surfaces. The transmission curves are more complex than those for simple rings, but provide more closely spaced reflection and transmission bands. In an example discussed here, a band centre frequency ratio of 1/1.3 is given by an array of compound elements with two concentric rings.     

Spectral-domain analysis of circular patch frequency selective surfaces

A computationally efficient method is presented for analyzing the scattering from frequency selective surfaces (FSS) comprised of circular metal patches. The formulation is carried out in the spectral domain where the convolution form of the integral equation for the induced current reduces to an algebraic one and the spectral-Galerkin technique is used to solve the resulting equation. Entire-domain basis functions that satisfy the edge condition are introduced to expand the unknown induced current on the metal patches. Calculated results using this procedure show good agreement with data reported by other authors.     

Scattering of waves from periodic surfaces

The scattering of waves from periodic surfaces is studied. We give a general review of this problem and compare three analytical methods for a conducting sinusoidal surface in detail for both TE and TM polarized waves. The three methods are: 1) the method developed by Masel, Merrill, and Miller (MMM); 2) the Modified Physical Optics (MPO) method; and 3) Waterman's Plane Harmonics (WPH) approach. We find the MMM method to be the most efficient one in terms of the rate and range of convergence. For dielectric media with periodic rough surfaces, an improved method is developed for calculating the reflected and transmitted powers. The results are used to compare with experimental data obtained at optical frequencies. It is shown that good agreement is achieved when the complex permittivity of the metal for the grating at the corresponding frequency is used.     

Element dependency in dielectric tuning of frequency selective surfaces

The dependence on substrate thickness of the resonance frequencies of dipole, square loop and circular patch FSSs is examined. Circular patches contain less fine scale structure, requiring fewer high order Floquet field modes. The evanescent fields are less tightly bound and the air/dielectric boundary is significant at greater substrate thicknesses.<>     

Scattering from conducting rough surfaces: a general perturbativesolution

The general term of the perturbation series is presented in closed form to treat scattering of horizontally polarized plane incident waves from a perfectly conducting rough surface. The use of the complete perturbation series obtained is illustrated through several examples of deterministic profiles, including the case of gently undulating surfaces (Kirchhoff limit) and the case of periodic gratings. Also, it is shown how specularity of the mean scattered field from statistically homogeneous surfaces can be proved in the present context     

Scattering of electromagnetic waves from moving surfaces

Electromagnetic wave scattering from moving objects is considered. Use is made of the reformulated current method in which the object is replaced by a current distribution radiating into an unbounded media. Cylindrical and spherical profiles in nondeterministic motion are considered. Results are obtained for far-field and steady-state cases when the radii of curvature are large compared to the wavelength.     

Interwoven convoluted element frequency selective surfaces with wide bandwidths

The interweaving of adjacent convoluted elements of crossed dipoles is shown to give reductions in operating frequencies of almost 15 times for single layer surfaces. The frequency stability with oblique incidence is observed to be significantly better than for simple crossed dipoles. At normal incidence the fractional reflection bandwidth increases to more than 60% and the common bandwidth for oblique incidence up to 45/spl deg/ is 46%.     

双层频率选择表面电磁特性数值模拟研究

给出了一种分析有介质加载的不同栅格外形双层频率选择表面电磁特性的数值模拟方法.介质分离区内前向波和反向波分别关于相应的频率选择表面是周期的,确定了矢量传输及衰减模的表述形式.应用电磁场边界条件获得不同Floquet模系数的矩阵表达式,推导出一组耦合的积分方程,利用矩量法求解得到结构的电磁散射特性.模拟结果表明,由于层间介质内电磁场衰减模的耦合,双层FSS结构的电磁传输特性较单层有很大的改善.     

有源频率选择表面研究进展及应用前景

有源频率选择表面(AFSS)是在传统频率选择表面(FSS)单元图形间加载一系列阻抗元件而构成的新型FSS,它具有可调的电磁特性。在分析了AFSS电磁特性调控机理的基础上,综述了AFSS在可调电磁屏蔽室、可调空间电磁滤波器、可调雷达天线等领域的研究进展,并重点阐述了AFSS在智能吸波结构上的应用,最后归纳了AFSS分析方法。     

Scattering from irregular-edged planar and curved surfaces

An electric field integral equation (EFIE) formulation is used to describe the electromagnetic scattering from finite planar and curved perfect electrical conducting surfaces truncated by an irregular edge. The edge can have an arbitrary form if it satisfies certain differentiability requirements. Similarly, the generating curve describing the surface can be convex, concave, or a combination of both. An edge-dependent entire domain Galerkin expansion is used for the current variation along the surface in the direction of translation. A subdomain expansion is used along the orthogonal direction. The backscatter cross sections obtained from the method of moments are compared with experimental data     

Self-similar prefractal frequency selective surfaces for multiband and dual-polarized applications

Frequency-selective surfaces (FSS), that have been designed using fractal iterative techniques, have been fabricated and measured. Fractals contain many scaled copies of the starting geometry, each of which acts as a scaled version of the original. A multiband FSS can be designed that uses several iterations of the geometry to form a prefractal that resonates corresponding to each of the scales present in the geometry. Minkowski and Sierpinski carpet fractals have been utilized in the design of three surfaces which exhibit two or three stopbands depending on how many iterations are used to generate the geometry of the cell. These surfaces are dual polarized due to the symmetry of the geometry. Simulation capabilities have been developed to analyze these periodic structures, including periodic method of moments (MOM) and finite-difference time-domain (FDTD) techniques which show good correlation to the measured results.