Analysis of frequency selective surfaces using two-parametergeneralized rational Krylov model-order reduction

Generalized rational Krylov model-order reduction techniques are applied to the spectral Galerkin system describing frequency selective surfaces, resulting in surface reflection coefficient models that depend on both the frequency and the incident angle of the exciting wave. The procedure is composed of three steps: construction of the spectral Galerkin system, linearization of that system, and reduction of the linearized system. The linearization of the spectral Galerkin matrix is carried out using two-dimensional (2-D) polynomial interpolation and the generation of a “two-parameter” companion form of the polynomial system. The subsequent model-order reduction is based on the concept of generalized Krylov subspaces, which are defined in the text. It results in a small system with a frequency and incident angle dependent output that matches the two-parameter polynomial interpolant system transfer function and its derivatives at many points in the frequency/incident angle plane. The technique is applied to the characterization of several frequency selective surfaces, and numerical results that demonstrate the accuracy of the techniques over a broad band of frequencies and range of incident angles are presented     

Analysis of frequency selective surfaces through the blazing onsetusing rational Krylov model-order reduction and Woodbury singularityextraction

Rational Krylov model-order reduction techniques are used to accelerate the characterization of frequency selective surfaces (FSSs) over broad spectral ranges, including frequencies at which a higher order Floquet mode stops evanescing and begins to propagate. The procedure comprises three main stages: (1) construction of the spectral Galerkin system at a small set of frequencies, (2) linearization of that system, and (3) reduction of the linearized system using the rational Krylov technique. The inclusion of blazing frequencies in the band of interest complicates the second and third of these steps because of the branch point singularity in the periodic Green's function. This difficulty is avoided by removing the blazing modes contributions to the spectral Galerkin matrix using the Woodbury formula for low-rank updates. The algorithm results in a set of small linear systems producing outputs that are combined to approximate the reflection and transmission coefficients of all propagating modes. The technique is applied to three different frequency selective surfaces and is shown to be accurate and efficient in all cases     

Frequency-selective surfaces to enhance performance of broad-band reconfigurable arrays

We present a novel frequency-selective surface (FSS) design aimed at enhancing the performance of broad-band reconfigurable antenna apertures. In particular, reconfigurable printed dipole arrays are examined in the presence of a multilayer FSS. Of particular interest is the design of FSS structures whose reflection coefficient has prespecified phase response over a broad set of frequencies. Previous FSSs primarily considered designs on the basis of the reflection coefficient amplitude and were intended for radome applications rather than substrates. Designing FSSs subject to phase requirements is seen to require some compromise in the magnitude. Broad-band requirements also present us with a need for noncommensurate FSS designs.     

多层频率选择表面的分析

本文利用矩量法和广义散射矩阵理论分析了多层频率选择表面的散射特性。通过引入广义波导概念,可以统一分析单元形状为任意的多层频率选择表面。作为示例,计算了几种不同结构频率选择表面的散射特性,结果与文献中给出的数据相符。     

宽带快速线性扫频激光光源的研制

报道了一种基于光栅多面镜调谐滤波器的宽带快速线性扫频激光光源。调谐滤波器由光栅和旋转多面镜组成,采用了非望远镜型利特罗布局,以简化滤波光学系统。在激光谐振腔中采用了自发辐射光谱范围互为拓展的双半导体光放大器,并将二者并联使用以确保宽光谱范围。研制的扫频激光光源的中心波长为1312 nm,扫频光谱范围为170 nm,半峰全宽为116 nm,对应于多面镜695 r/s的转速,扫频速度达到50 kHz,相应的激光输出平均功率为2 mW。该宽带快速线性扫频激光光源,尤其适用于高分辨扫频光学相干层析成像系统,轴向分辨率能达到6.5μm。     

基于节点编码的区域分解算法及其在二维散射中的应用

研究了一种高效率的基于节点编码的区域分解算法.将原始的求解区域分割为若干个相对独立的子区域,使原问题转化为若干个相对独立的子问题,通过求解公共边界上的场值,可以快速获得整个求解区域上的场值,极大地减少了存储量和计算量.此外,这种区域分解算法不仅能够快速、高效、并行地计算电大尺寸柱体的电磁散射,还特别适合于求解具有几何重复性特征的结构,如天线阵列、有限周期频率选择表面、PBG/EBG等的电磁仿真问题.数值算例验证了该方法的准确性和有效性.     

Analysis and synthesis of multiband dual polarized parallel metallic strips FSS with a ring using WCIP method

In this paper parallel metallic strips FSSs with a ring are introduced and analyzed by the WCIP method for their simple modeling characterized by independent resonant frequencies due to its non-coupled metallic elements. Two FSS structures are manufactured and measured. A FSSs synthesis approach is presented and the curves relating the desired resonant frequencies to the FSS metallic elements lengths responsible of theses frequencies are plotted. To test the synthesis, approach the two manufactured FSSs frequency responses are taken as the desired ones and the proposed synthesis approach is used to determine the metallic strips and the ring lengths for the FSSs unit cell. WCIP results are compared to measurements and a good agreement is observed. For complex pattern FSS the resonant frequencies sources are not always easy to be determined. Thus an equivalent FSS based on metallic strips and a ring can be used maintaining the same frequency response in the limit of the proposed approach. The synthesis approach is used to determine its equivalent FSS structure of a published complex FSS pattern. WCIP method and HFSS software results of the equivalent FSS are compared to published measurements and a good agreement is recorded.     

Efficient large-domain MoM solutions to electrically largepractical EM problems

A numerical method is presented for the analysis and design of a wide variety of electromagnetic (EM) structures consisting of dielectric and conducting parts of arbitrary shapes. The method is based on the integral-equation formulation in frequency domain, and represents a large domain (high-order expansion) Galerkin-type version of the method of moments (MoM). The method is formulated in two versions concerning the type of the equivalence (volume and surface) utilized in the treatment of the dielectric parts of the structure. The generality, versatility, accuracy, and practicality of the method and code are demonstrated on four very diverse, electrically large, and complex EM problems. The examples are: an X-band reflector antenna modeled after a bat's ear, which is about 11λ³ large at X-band; a broad-band (0.5-4.5 GHz) nested array of crossed loaded dipoles; an EM system consisting of a dipole antenna and a human body, and a broad-band (1-5 GHz) microstrip-fed Vivaldi antenna with a high-permittivity dielectric substrate. The central processing unit times with a modest personal computer are on the order of several minutes for a single-frequency application     

A 4-, 6-, 20-, and 30-GHz-Band Branching Network Using a Multilayer Dielectric Filter for a Satellite Communication Earth Station

This paper describes a four-frequency broad-band branching network for transferring microwave (4 and 6 GHz)- and millimeter-wave (20 and 30 GHz)-band signals between an antenna and transmitter-receivers in a satellite communication earth station. A filter for separating the microwave band from the millimeter-wave band employs a multilayer dielectric filter with matching layers and is included in the primary antenna feed system. The design method used for the multilayer dielectric filter and the construction and experimental results of the four-frequency broad-band branching network are described. Measurements show that its insertion loss, VSWR, and axial ratio are less than 1.2, 1.2, and 2.1 dB, respectively.     

Creating accurate multivariate rational interpolation models ofmicrowave circuits by using efficient adaptive sampling to minimize thenumber of computational electromagnetic analyses

A fast and efficient adaptive sampling algorithm for multivariate rational interpolation models based on convergents of Thiele-type branched continued fractions (BCFs) is presented in this paper. We propose a variation of the standard BCF that uses approximation to establish a nonrectangular grid of support points. Starting with a low-order interpolant, the technique systematically increases the order by optimally choosing new support points in the areas of highest error until the required accuracy is achieved. In this way, accurate surrogate models are established by a small number of support points without any a priori knowledge of the data. The technique is evaluated on several passive microwave structures     

Novel waveguide filters with multiple attenuation poles using dual-behavior resonance of frequency-selective surfaces

This paper develops novel waveguide filters consisting of frequency-selective surfaces (FSSs) in order to realize both the drastic size reduction and multiple attenuation poles in stopbands at both sides of passband. The FSS provides not only a passband but also attenuation-pole frequencies in stopbands since the FSS has both the aperture-element and the patch-element behaviors. In the present design method, the shape of each FSS is designed by a genetic algorithm so that the resonant curve of FSS can be fitted to that obtained from an equivalent-circuit approach. By using such FSSs and quarter-wavelength waveguides, a bandpass filter with six attenuation poles like an elliptic-function filter has been constructed. Furthermore, a technique of the size reduction by controlling adequately the resonant response of each FSS is presented. In this filter, the FSSs are closely located at the interval of the length much shorter than a quarter wavelength. It is shown from the design example that the half longitudinal length of the former example can be obtained, keeping both the passband response and attenuation poles in stopbands. The effectiveness of the waveguide filters with FSSs is validated by good agreement between the calculated and the measured results.     

封闭式隐身桅杆的初步设计与效果评估

以一个典型的桅杆-天线系统为例,探讨了封闭式隐身桅杆的设计方法,形成了桅杆-天线系统隐身初步设计原则。为了保障电磁收发设备的正常工作,研究了封闭式桅杆上透波窗的设计方法和相应的频率选择表面(FSS:Frequency Selective Surface)技术。对封闭式隐身桅杆方案与普通桅杆的电磁散射性能进行了对比分析。结果表明:封闭式隐身桅杆能在宽广的角域范围内有效降低桅杆-天线系统的雷达散射截面(RCS:Radar Cross Section),大幅度提高桅杆-天线系统的隐身性能。     

SPICE equivalent circuits of frequency-domain responses

The paper proposes a method for the synthesis of SPICE-compatible broad-band electrical models of frequency-domain responses approximated by rational functions. First- and second-order equivalent circuits with controlled sources are used as building blocks to generate equivalent circuit representations-totally compatible with commercial circuit solvers - of the frequency-dependent responses. Fundamental properties of the method are discussed and details of its implementation are described. The proposed approach has demonstrated to be suitable for providing equivalent circuits of interconnects, power/ground plane structures and PCB discontinuities.     

"时间窗"对天线时域平面近场测试结果的影响

天线时域近场测试技术是一种新兴的、测试宽带场和工作在窄脉冲激励下天线辐射场的高效的测试技术.因为它可以利用"时间窗"技术进行信号处理,使其相对频域测试具有独特的优势.本文在已建立的天线时域近场测试系统的基础上,从实验的角度,对"时间窗"参数在天线时域平面近场测试中的影响进行验证分析.举例了三个波段标准天线方向图的测试分析结果,并得出初步结论.     

宽带平坦增益光纤喇曼放大器最新进展

在整个工作波段内具有较好的增益平坦度是对应用在波分复用光纤通信系统中的光纤喇曼放大器的一个基本要求.在光纤喇曼放大器的数学模型的基础上分析了实现其平坦增益的几种方法,然后对宽带平坦增益光纤喇曼放大器的最新进展进行了综合评述,最后对其发展进行了展望.     

基于SRR结构的多频带频率选择表面

为实现频率选择表面(FSS)的多频带特性,将开口谐振环(SRR)结构引入多频带FSS的设计中.基于等效电路和仿真模型分析了单个SRR的电磁谐振特性,及其作为FSS结构单元而产生的电磁耦合.最后,利用有限元仿真软件HFSS计算了理想状态下无穷大周期性结构的多频带FSS,并通过对FSS的传输和反射频谱研究,揭示这种FSS谐振频率与SRR结构基本几何参数的内部关系.     

Performance improvement of a self-heterodyne detection BOTDR system employing broad-band laser

The self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR) system using broad-band laser is proposed to reduce coherent Rayleigh noise and improve the system performance. Compared with the system with narrow-band laser, the stimulated Brillouin scattering (SBS) threshold can be improved by about 3 dB. The experimental results of the narrow-band laser measurements for three times independently and the broad-band laser measurement for one time are compared. The root-mean-square (RMS) errors of Brillouin linewidth for two systems with narrow-band laser and broad-band laser are 6.9 MHz and 2.7 MHz, respectively, and the RMS errors of temperature for the heated fiber are about 1.3 °C and 0.7 °C. With the broad-band laser, signal-to-noise ratio (SNR) of the unheated fiber is approximately equivalent to that of the integrated three independent Brillouin signals for the narrowband laser, and the results are believed to be beneficial for performance improvement and measurement time reduction.     

Polygonal patch antennas for wireless communications

An effective design of polygonal patch antennas with multifrequency or broad-band operation modes for wireless communications is presented in this paper. It is shown how polygonal patches with suitable features may be obtained after a proper perturbation of conventional rectangular geometries, which inherently present poor bandwidth performances. These perturbed irregular geometries may support multiple resonances and, thus, may present a broad-band or multifrequency operation mode, even employing conventional patch antennas with a single dielectric substrate. These polygonal patches are efficiently analyzed through a numerical code based on the method of moments, with entire domain basis functions that accurately describe the radiation mechanism. After the presentation of the analysis and design techniques, some antenna layouts for modern wireless communication systems will be proposed. Such antennas are designed for both universal mobile telecommunication system and wireless local area network portable equipment with real-life finite ground planes.     

A New Technique for Design of Low-Profile, Second-Order, Bandpass Frequency Selective Surfaces

In this study, a new method for designing low profile frequency selective surfaces (FSS) with second-order bandpass responses is presented. The FSSs designed using this technique utilize non-resonant subwavelength constituting unit cells with unit cell dimensions and periodicities in the order of $0.15lambda _{0}$. It is demonstrated that using the proposed technique, second-order FSSs with an overall thickness of $lambda _{0}/30$ can be designed. This is considerably smaller than the thickness of second-order FSSs designed using traditional techniques and could be particularly useful at lower frequencies with long wavelengths. To facilitate the design of this structure, an equivalent circuit based synthesis method is also presented in this paper. Two bandpass FSS prototypes operating at X-band are designed, fabricated, and tested. A free space measurement setup is used to thoroughly characterize the frequency responses of these prototypes for both the TE and TM polarizations and various angles of incidence. The frequency responses of these structures are shown to have a relatively low sensitivity to the angle of incidence. Principles of operation, detailed design and synthesis procedure, and measurement results of two fabricated prototypes are presented and discussed in this paper.      

Design and Testing of Frequency-Selective Surfaces on Silicon Substrates for Submillimeter-Wave Applications

A new class of frequency-selective surfaces (FSSs), to be used as quasi-optical filters for harmonic suppression in submillimeter-wave frequency multipliers, is proposed and experimentally verified. The FSSs consist of two-dimensional aperture arrays and are made from microstructured aluminum on electrically thick, high-resistivity silicon substrates. This leads to a very good mechanical stability, reasonably low insertion loss, and permits manufacture of the structure by using standard processes available from the semiconductor industries. This paper presents the design, fabrication, and testing of two sets of prototypes, the former with a passband at 300 GHz and a stopband at 450 GHz and the latter with a passband at 600 GHz and a stopband at 750 GHz. For both frequency ranges, FSSs with rectangular slots and with dogbone-shaped holes have been designed by using the method of moments/boundary integral-resonant mode expansion method. The effect of ohmic and dielectric losses has been determined by using the commercial code HFSS. Several prototypes have been fabricated, and measured by terahertz time-domain spectroscopy and continuous wave measurements, showing high reproducibility of the machining process, insertion loss between 1.0 and 1.6 dB, and stopband attenuation larger than 30 dB. Finally, we demonstrate that the incidence angle can be used as a degree of freedom for fine tuning the stopband, without practically changing the frequency response in the passband.