多层快速多极子算法中的两步插值技术

多层快速多极子算法(MLFMA)在快速多极子算法(FMM)的基础上按多层聚集、层间转移和多层扩散的思路以达到优化矩阵向量积的运算的目的,其中多层聚集和多层扩散过程,随着层数递增,角谱积分采样点数逐层递增,为了快速计算角谱积分,需要采用插值技术和反插值技术以提高计算效率.应用两步插值技术替代传统的单步插值技术,大幅提高了多层快速多极子层间插值反插值操作的计算效率,对于应用普通个人计算机求解特大电大尺寸问题,具有重要意义.     

天线方向系数的一类计算逼近方法

天线的方向系数是天线的核心性能指标之一,准确计算方向系数是高性能天线应用的核心要求.本文基于平面近场测试理论、实测数据和快速傅里叶变换算法,系统阐述基于近场测试来数值计算天线方向系数的原理,并进行深入的误差分析.本文选择一种方向图函数和方向系数已知的被测天线,来检验所讨论的误差评估方案.评估分两步实现,第一步,针对这一天线,采用标准的近场测试配置,仿真模拟出(相当于实际测量出)一套平面近场数据.第二步,基于这套近场数据,利用数值积分计算出天线方向系数.本文使用或提出了四种数值算法,分析了提出的后三种算法本身的误差来源,并开发出程序搜索方案,确定出后两种算法的最小误差界.随后,利用这四种数值算法分别得出天线的方向系数.结果表明,计算所得的近场方向系数都比真实方向系数大,但误差不超过0.6 d B.这一结果对实际应用中正确评估基于近场测试的天线方向系数准确性有重要参考价值.     

水面目标复合电磁散射的并行迭代快速计算

采用快速远场近似的降秩电磁流迭代法计算目标与粗糙水面的复合散射, 并进一步采用粗糙面分区的多进程并行迭代算法提高其计算速度, 分析了降秩电磁流迭代法对散射结果的影响, 表明该方法可用于近场复合散射问题的计算; 对平板目标与水面间的复合散射进行了计算, 计算结果与快速多极子方法(MLFMM)结果符合较好, 验证了该算法的有效性. 同时, 利用造波水池开展了目标与水面近场复合散射的模拟实测, 测试与计算结果趋势较为一致.     

具有高隔离度的双陷波超宽带多入多出天线

提出了一款具有高隔离度的双陷波超宽带多入多出(UWB MIMO)天线。该天线由两个相同的半切超宽带天线单元倒置构成。通过在天线底板刻蚀栅栏型缺陷地解耦结构,使该MIMO天线的隔离度提高至25 dB。此外,在天线半圆形辐射贴片上刻蚀两个方向相反的"L"型缝隙,实现了双陷波的功能,分别抑制了802.16无线城域网WiMAX(3.2~3.7 GHz)和WLAN(5.15~5.85 GHz)信号对天线系统的干扰。实验结果表明,该天线在3~11 GHz工作带宽内的隔离度大于25 dB,包络相关系数(ECC)小于0.004;第一个陷波频段为3.0~3.7 GHz,第二个陷波频段为5.1~5.85 GHz,有效抑制了WiMAX和WLAN的信号干扰。     

超越SNOM探针通光孔径尺寸的金属纳米间隙超分辨测量

采用电磁场有限元方法,数值模拟了孔径型扫描近场光学显微镜(aperture Scanning Near-field Optical Microscopy,a-SNOM)在照明模式下的工作过程.针对金偶极天线结构,改变天线长度和纳米间隙尺寸,计算了a-SNOM探针孔径的远场辐射速率随探针端面中心坐标变化的扫描曲线,实现了超越a-SNOM探针通光孔径尺寸的天线金属纳米间隙的超分辨测量,对于100nm通光孔径的探针,可分辨最小尺寸为10nm(0.016倍波长)的金属间隙.通过对比金属和介质偶极天线的a-SNOM探针远场辐射速率测量的计算结果,表明天线金属纳米间隙的超分辨测量的实现是由于金属间隙表面等离激元的激发.     

积分方程平面反射阵电磁建模技术北大核心CSCD

针对基于空间功率合成的空馈平面反射阵(FLAPS)型高功率微波辐射器的高效率电磁仿真需求,应用积分方程方法结合多尺度混合电磁建模技术MLFMA-MLACE进行问题的电磁建模及求解,主要过程包括:针对设计模型进行多尺度几何建模;在宏观层面采用多层快速多极子加速矩矢相乘;在微观层面采用多层笛卡尔展开加速求解。结合W波段的FLAPS初步模型,利用传统多层快速多极子技术(MLFMA)进行了精度验证,对于混合方法在仿真中的适用性、模型等效处理程度的影响以及计算成本等进行了分析。结果表明,该方法在内存及计算时间方面显著地提高了效率,论文还对后续改进方向进行了讨论。     

激光通信地面测试终端间隔离度的仿真分析

受空间所限,激光通信地面测试平台与被测终端之间的距离远小于实际通信距离,导致测试平台光机等器件产生的后向散射杂光进入被测终端,从而严重影响被测终端的测试性能。从被测终端与测试平台间的光学干扰问题出发,本文研究了被测终端与测试平台间隔离度的关系,分别设计了卡塞格林和离轴三反光学天线,并根据杂散光传输模型,采用杂散光分析软件分析了光学天线结构形式及表面粗糙度两方面对隔离度的影响。分析结果表明,采用离轴三反光学天线时的隔离度明显高于卡塞格林光学天线,且隔离度随着光学表面粗糙度的减小而增大,当光学表面的粗糙度达到0.892 nm时,隔离度可达-86.22 dB。最后,推导了ABg模型与Harvey模型参数间的关系,并根据粗糙度与TIS计算公式,得出粗糙度分别为0.7 nm及0.5 nm的ABg模型参数,它们的终端间隔离度分别为-94.39 dB和-97.3 dB,实现了-90 dB的隔离度指标。     

随机相位微波功率的空间合成效率

 采用数值计算方法,将微波功率源输出信号的相位差视为等概率分布的随机事件,通过阵列天线平均增益定量计算了多微波源空间功率合成效率;分析了随机相位条件下,天线单元间耦合系数、极化方式和单元增益对合成效率的影响。计算结果表明：多微波源在随机相位条件下进行空间功率合成,阵列天线单元之间的相互耦合将造成合成效率严重下降;而天线类型、极化方式和天线单元增益对合成效率的影响较小。     

一种高功率微波空间滤波器的设计与初步实验研究

研究了一种新型高功率微波空间滤波器(双工器),该空间滤波器通过放置在天线近场的周期性金属圆柱阵列实现线极化波的反射和透射.通过对比研究低功率条件下放置该双工器前后的辐射方向图,发现该双工器对S波段微波的反射效率达到96%,对X波段微波的透射效率达到97%,隔离度分别达到25dB以上,交叉耦合度在-25dB以下.在S/X波段各自注入1.5GW的高功率微波,脉冲宽度为100ns的条件下,放置双工器后没有发现明显的微波脉冲缩短现象.     

聚焦条件下的高斯波束矩形口径天线近场分析

 采用口径场法对聚焦条件下具有高斯波束的矩形口径天线近场进行了分析,得到了聚焦条件下的近场场强分布与近场增益解析式,并对不同的聚焦位置进行了仿真。结果表明：在近场区,聚焦位置离轴向越近,其场强越强,且增益越大,聚焦位置沿轴向时其场强与增益皆为最大;反之,聚焦位置离轴向越远,其近场场强与近场增益越小。因此,通过聚焦可以显著提高天线口径面场的近场场强与增益指标,从而提高天线系统的有效作用距离。     

Multilevel fast multipole algorithm for acoustic wave scattering by truncated ground with trenches

The multilevel fast multipole algorithm (MLFMA) is extended to solve for acoustic wave scattering by very large objects with three-dimensional arbitrary shapes. Although the fast multipole method as the prototype of MLFMA was introduced to acoustics early, it has not been used to study acoustic problems with millions of unknowns. In this work, the MLFMA is applied to analyze the acoustic behavior for very large truncated ground with many trenches in order to investigate the approach for mitigating gun blast noise at proving grounds. The implementation of the MLFMA is based on the Nystrom method to create matrix equations for the acoustic boundary integral equation. As the Nystrom method has a simpler mechanism in the generation of far-interaction terms, which MLFMA acts on, the resulting scheme is more efficient than those based on the method of moments and the boundary element method (BEM). For near-interaction terms, the singular or near-singular integrals are evaluated using a robust technique, which differs from that in BEM. Due to the enhanced efficiency, the MLFMA can rapidly solve acoustic wave scattering problems with more than two million unknowns on workstations without involving parallel algorithms. Numerical examples are used to demonstrate the performance of the MLFMA with report of consumed CPU time and memory usage.     

A low frequency stable plane wave addition theorem

The multilevel fast multipole algorithm (MLFMA) is a well known and very successful method for accelerating the matrix-vector products required for the iterative solution of Helmholtz problems. The MLFMA has an important drawback, namely its inability to handle scattering problems with a lot of subwavelength detail due to the low frequency (LF) breakdown of the MLFMA. There is a need to extend the MLFMA to LF, since alternative methods are less efficient (multipole methods) or hard to implement (spectral methods). In this paper a new addition theorem will be developed that does not suffer from an LF breakdown. Instead it suffers from a high-frequency (HF) breakdown. The new method relies on a novel set of distributions, the so-called pseudospherical harmonics, closely related to the spherical harmonics. These allow the discretization points and translation operators to be calculated in closed form. Hence the method presented in this paper allows the easy implementation of a method that is stable at LF. Furthermore, a combination of the traditional MLFMA and the new method allows for the construction of a broadband MLFMA.     

快速计算地面上车辆目标的电磁散射特性

为快速计算地面上车辆目标的电磁散射特性,实现适用于半空间环境的多层快速多极子方法.对于近区项,利用严格的半空间并矢格林函数进行计算;对于远区项,首先将半空间格林函数分解为直射项和反射项,然后采用实镜像方法计算反射项.方法物理概念清晰,与目前常用的离散复镜像方法相比,具有良好的收敛性和稳定性,大大降低计算时间和内存需求.实例计算并分析地面上汽车模型的电磁散射特性.     

A Plane-Wave Beam-Steering Lens Design Using Microstrip Switched-Line Phase Shifters

A compact beam-steering lens design appropriate for millimeter-wave and submillimeter-wave applications is experimentally verified with an X-band test model. The lens achieves coupling to plane-wave beams through arrays of patch antennas placed on its two outer surfaces. The isolation between input and output antennas is accomplished by inserting a metal ground plane in the middle of the lens. The two closest patch antennas on the front and the backside are connected together with microstrip circuits that include switched-line phased shifters and interconnecting vias through the lens substrate. Three different X-band 100-element plane-wave microstrip lenses that use passive delay lines instead of actual phase-shifters were fabricated to successfully demonstrate the beam-steering angles of 20 and 40 degrees. From a separate waveguide measurement on the unit-cell element only, the insertion loss of the lens was estimated to be approximately 3.5 dB with bandwidth of 2% at 10 GHz.     

Decoupling technique of patch antenna arrays with shared substrate by suppressing near-field magnetic coupling using magnetic metamaterials

In this paper,we propose the decoupling technique of patch antenna array by suppressing near-field magnetic coupling(NFMC) using magnetic metamaterials.To this end,a highly-integrated magnetic metamaterials,the substrate-integrated split-ring resonator(SI-SRR),is firstly proposed to achieve negative permeability at the antenna operating frequency.By integrating SI-SRR in between two closely spaced antennas,magnetic fields are blocked in the shared substrate due to negative permeability of SI-SRR,reducing NFMC between the two antennas.To verify the technique,a prototype was fabricated and measured.The measured results demonstrated that the isolation can be enhanced by more than 17 dB even when the gap between the two patch antennas is only about 0.067 A.Due to high integration,this technique provides an effective alternative to high-isolation antenna array.     

Integration of microbolometers with infrared microstrip antennas

We report on various integration schemes of infrared microbolometers with microstrip antennas. The first integration design consists of two gold (Au) rectangular microstrip patches coupled along the radiating edges by a narrow niobium (Nb) strip. Devices using silicon oxide are compared to devices using amorphous silicon as antenna substrate. An extension of the twin-patch detector design is the microstrip dipole antenna-coupled microbolometer. Two ways of connecting the device to the contact pads via narrow dc leads are presented and compared. The contribution of the dc leads to the detector response is eliminated by directly connecting the dipole to the contact pads. The thermal isolation of the microbolometer from the silicon wafer is improved by incorporating air into the antenna dielectric substrate. This leads to higher detector responsivity and shifts the resonance towards longer antennas. The implementation of a bridge microstrip dipole antenna structure is also discussed.     

Millimeter wave monolithic schottky diode imaging arrays

Planar Schottky diodes are integrated with bow-tie antennas to form a one-dimensional array. The energy is focused onto the antennas through a silicon lens placed on the back of the gallium-arsenide substrate. A polystyrene cap on the silicon lens reduces the reflection loss. A self-aligning process with proton isolation has been developed to make the planar Schottky diodes with a 1.1-THz zero-bias cutoff frequency. The antenna coupling efficiency and imaging properties of the system are studied by video detection measurements at 94 GHz. As a heterodyne receiver, a double-sideband mixer conversion loss of 11.2 dB and noise temperature of 3770°K have been achieved at a local oscillator frequency of 91 GHz. Of this loss, 6.2 dB is attributed to the optical system and the antenna.     

MLFMA用于三维电大复杂腔体电磁散射特性的快速计算

基于迭代物理光学法的多层快速多极子算法可高效、快速求解电大腔体的散射特性,给出混合算法的迭代公式.对工程上常见的弯曲较缓慢的S弯腔体,通过合适的分段结构化分组,避免两组之间存在的部分面元遮挡的情况,应用广义互易积分处理带有复杂终端的腔体.数值计算结果表明,所用方法准确并能极大地提高计算速度.     

Performance analysis and comparison of MWCNT loaded ITO and TIO based optically transparent patch antennas for terahertz communications

Multiwalled carbon nanotube (MWCNT) loaded transparent conducting oxide materials (TCOMs) based optically transparent antennas are designed to resonate at 750 GHz. TCOMs such as indium-doped tin oxide (ITO) and titanium-doped tin oxide (TIO) are used for designing the transparent terahertz patch antennas. Shorting pin technique is used to improve the impedance performances of the transparent antennas. The MWCNT is used for shorting the microstrip line with the ground plane of the antenna. By varying the position of short with respect to the antenna patch, the resonant frequency of the antennas are optimized to resonate at 750 GHz. The impedance and radiation performances of the MWCNT loaded transparent antennas are compared. A broad impedance bandwidth (−10 dB) is achieved for both the proposed antennas. The MWCNT shorting pin effect on radiation performances of the transparent antennas are discussed in detail. The antennas are simulated using finite element method (FEM) based electromagnetic solver, Ansys-HFSS.