Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays

The maximum power conversion efficiencies of the top-emitting,oxide-confined,two-dimensional integrated 2×2 and4×4 vertical-cavity surface-emitting laser（VCSEL） arrays with the oxide-apertures of 6 μm,16 μm,19 μm,26 μm,29 μm,36 μm,39 μm,and 46 urn are fabricated and characterized,respectively.The maximum power conversion efficiencies increase rapidly with the augment of oxide-aperture at the beginning and then decrease slowly.A maximum value of27.91%at an oxide-aperture of 18.6 μm is achieved by simulation.The experimental data are well consistent with the simulation results,which are analyzed by utilizing an empirical model.

Distributed genetic algorithm for optimal planar arrays of aperture synthesis telescope

Sparse arrays of telescopes have a limited (u, v)-plane coverage. In this paper, an optimization method for designing planar arrays of an aperture synthesis telescope is proposed that is based on distributed genetic algorithm. This distributed genetic algorithm is implemented on a network of workstations using community communication model. Such an aperture synthesis system performs with imperfection of (u, v) components caused by deviations and(or) some missing baselines. With the maximum (u, v)-plane coverage of this rotation-optimized array, the image of the source reconstructed by inverse Fourier transform is satisfactory.

Encoding methods matching the 16×16 pixel CZT detector of a coded aperture gamma camera

With the advancements in nuclear energy,methods that can accurately obtain the spatial information of radioactive sources have become essential for nuclear energy safety.Coded aperture imaging technology is widely used because it provides two-dimensional distribution information of radioactive sources.The coded array is a major component of a coded aperture gamma camera,and it affects the key performance parameters of the camera.Currently,commonly used coded arrays such as uniformly redundant arrays(URAs)and modified uniformly redundant arrays(MURAs)have prime numbers of rows or columns and may lead to wastage of detector pixels.A 16×16 coded array was designed on the basis of an existing 16×16 multi-pixel position-sensitive cadmium zinc telluride detector.The digital signal-to-noise(SNR)ratio of the point spread function at the center of the array is 25.67.Furthermore,Monte Carlo camera models and experimental devices based on rank-13 MURA and rank-16 URA have been constructed.With the same angular resolution,the field size of view under rank-16 URA is 1.53 times that of under rank-13 MURA.Simulations(Am-241,Co-57,Ir-192,Cs-137)and experiments(Co-57)are conducted to compare the imaging performance between rank-16 URA and rank-13 MURA.The contrast-to-noise ratio of the reconstructed image of the rank-16 array is great and only slightly lower than that of rank-13 MURA.However,as the photon energy increases,the gap becomes almost negligible.

Improving Airgun Signal Detection with Small-Aperture Seismic Array in Yunnan

Repeating airgun sources are eco-friendly sources for monitoring the changes in the physical properties of subsurface mediums,but their signals decay quickly and are buried in the noises soon after traveling short distances.Stacking waveforms from different airgun shots recorded by a single seismic station(shot stacking)is the most popular technique to detect weak signals from noisy backgrounds,and has been widely used to process the data of Fixed Airgun Signal Transmission Stations(FASTS)in China.However,shot stacking sacrifices the time resolution in monitoring to recover a qualified airgun signal by stacking many shots at distance stations,and also suffers from persistent local noises.In this paper,we carried out several small-aperture seismic array experiments around the Binchuan FAST Station(BCFASTS)in Yunnan Province,China,and applied the array technique to improve airgun signal detection.The results show that seismic array processing combining with shot stacking can suppress seismic noises more efficiently,and provide better signal-to-noise ratio(SNR)and coherent airgun signals with less airgun shots.This work suggests that the array technique is a feasible and promising tool in FAST to increase the time resolution and reduce noise interference on routine monitoring.

A New Dual Polarized Aperture-Coupled Printed Array for SAR Applications

This paper presents a new design of dual polarized aperture coupled printed antenna array. The finite difference time domain (FDTD) analysis of an aperture coupled microstrip element is performed, and the effects of antenna parameters on its characteristics are obtained to guide the design of the printed array. Then an 8×2 dual polarized array design in X band is introduced with configuration plots. In order to improve its isolation and cross polarization, an outphase displacement feeding technique is adopted in the feed network. Also, the round bends are used instead of conventional right angle bends so as to achieve better VSWR performance. Experimental results are presented, indicating the validity of the design. This dual polarized array can be applied as a sub array of spaceborne SAR systems.

A FAST SEARCH METHOD OF STEERED RESPONSE POWER WITH SMALL-APERTURE MICROPHONE ARRAY FOR SOUND SOURCE LOCALIZATION

The Steered Response Power(SRP)method works well for sound source localization in noisy and reverberant environment.However,the large computation complexity limits its practical application.In this paper,a fast SRP search method is proposed to reduce the computational complexity using small-aperture microphone array.The proposed method inspired by the SRP spatial spectrum includes two steps:first,the proposed method estimates the azimuth of the sound source roughly and determines whether the sound source is in far field or near field;then,different fine searching operations are performed according to the sound source being in far field or near field.Experiments both in simulation environments and real environments have been performed to compare the localization accuracy and computation complexity of the proposed method with those of the conventional SRP-PHAT algorithm.The results show that,the proposed method has a comparative accuracy with the conventional SRP algorithm,and achieves a reduction of 93.62%in computation complexity compared to the conventional SRP algorithm.

PERFORMANCE ANALYSIS OF PULSE COMPRESSION USING PHASE-CODED SIGNALS FOR SPARSE-ARRAY SYNTHETIC IMPULSE AND APERTURE RADAR

Sparse-array Synthetic Impulse and Aperture Radar (SIAR) can isotropically radiate by employing multiple frequencies (synthetic pulse) and multiple antennas (synthetic antenna). According to Ambiguity Function(AF), its range resolution depends only on bandwidth of transmitted signals, however, the distance grating lobes emerge when increasing the time-bandwidth product of transmitted signals. The performance of pulse compression is analyzed with the transmitted signals modulated by phase-coded sequences. It is seen that greater ratio of pulse compression and suppression of range sidelobe in SIAR can be obtained, and its effective range and range resolution is increased as well.

CROSS-TRACK THREE APERTURES MILLIMETER WAVE SAR SIDE-LOOKING THREE-DIMENSIONAL IMAGING

The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-track direction, and three virtual phase centers will be obtained through one-input and three-output. These three virtual phase centers form a sparse array which can be used to obtain the cross-track resolution. Because the cross-track array is short, the cross-track resolution is low. When the system works in side-looking mode, the cross-track resolution and height resolution will be coupling, and the low cross-track resolution will partly be transformed into the height uncertainty. The beam pattern of the real aperture is used as a weight to improve the Peak to SideLobe Ratio (PSLR) and Integrated SideLobe Ratio (ISLR) of the cross-track sparse array. In order to suppress the high cross-track sidelobes, a weighting preprocessing method is proposed. The 3D images of a point target and a simulation scene are achieved to verify the feasibility of the proposed method. And the imaging result of the real data obtained by the cross-track three-baseline MMW InSAR prototype is presented as a beneficial attempt.

Aperture Efficiency Study of Square Reflect Array Antennas

This paper presents a detailed study of square reflect array (RA) antenna aperture efficiency (ηa). Effects of quantization-phase and limited phase-range errors on radiation pattern, half-power beam width (HPBW) and ηa for different feed locations are investigated. Results show an in-crease in side-lobe levels (SLLs) and a slightly reduction in ηa with quantization-phase augmentation or element phase-range reduction, however, the effects on HPBW are negligible. Nevertheless, the degradation in ηa is negligible when the quantization-phase is lower than 30° or phase-range is more than 300°. Parametric studies have been carried out to provide design guidelines to maximize ηa. It is perceived that the offset-angle plays an important role to determine ηa, especially for feed with narrow beam width.

基于遗传算法的双频共孔径稀疏天线阵列

针对卫星通信和数据传输等应用,提出了一款基于遗传算法的双频(Ku/S)共孔径稀疏阵列天线。该阵列天线具有剖面低、集成度高、副瓣低等优点。双频天线阵列在单一圆孔径中集成了稀疏排布的高频段(Ku:17 GHz)阵列与低频段(S:2.25 GHz)阵列,其中高频阵列排布方式基于遗传算法优化得到,具有低副瓣,高增益的特点,并为低频阵列的嵌入提供物理空间;低频阵列以三圈圆环阵列形式嵌入高频阵列中,可进一步优化高频阵列以保持高低频阵列均处于最优状态。所提出的双频天线阵列在60°扫描范围内获得高低频增益分别为26 dBi和15 dBi,均具有≥20 dB的副瓣抑制,且相对于全阵列天线,优化后阵面尺寸仅为原尺寸的60%。

一种分布式孔径阵列中的同步和校正方法

分布式孔径阵列实现了传统大孔径雷达的效能,规避了传统大孔径雷达的弊端,但因其体制特点带来新的问题。不同孔径单元之间有同步误差,以及接收机通道间的幅相不一致性,这些误差会造成相控阵天线接收波束的指向发生变化、副瓣增高、天线增益下降等一系列问题,导致分布式孔径阵列性能下降。为了实现分布式系统的全相参工作,需要各单元雷达之间时间、空间和相位的同步。本文采用单元间同步和内校正的方法实现了分布式孔径阵列的同步,并在工程应用中取得了较好的效果。

机载有源相控阵火控雷达技术发展

机载火控雷达是战斗机平台获取信息的主要传感器,经历了测距机、脉冲雷达、脉冲多普勒雷达、相控阵雷达的发展历程。文中通过对现有战斗机火控雷达现状分析,结合未来战斗机平台作战需求分析等多个角度分析对机载火控雷达的需求和技术牵引,结合射频一体化、分布式探测、智能蒙皮、隐身探测和芯片化等新兴技术,展望未来机载火控雷达发展趋势,为后续机载火控雷达设计与研究提供参考借鉴。

Ka频段卫通收发共口径多波束相控阵封装天线设计

为满足卫星通信中双频共口径、高集成、多波束等要求,提出了一种基于封装天线(Antenna in Package, AIP)架构的Ka频段收发共口径多波束相控阵天线。天线以双频堆叠微带单元的形式实现了收发共口径,并通过天线集成滤波器保证了收发通道的隔离度优于44 dB。在±60°范围内,64元接收阵增益优于17.4 dB,128元发射阵增益优于20.2 dB,具有良好的波束扫描性能。为获得收发多波束一片式集成,在收发(Transmitter/Receiver, T/R)组件中使用晶圆级三维系统集成封装(Three Dimensions System in Package, 3D-SIP)并结合微凸点的制备技术,保证了系统级芯片(System-on-Chip, SOC)的高密度二次集成。高低频混压技术同样被应用于阵面、收发网络、控制供电链路的多层板集成。所提多波束的相控阵天线新架构具有高密度集成TR组件、多波束一体化、高效散热等特点,在卫星通信和数据链等方面具有广阔的应用前景。

基于频率分集阵列小埋体检测三维形貌成像方法

频率分集阵列(Frequency Diverse Array,简称FDA)在埋体管线的探测识别与成像中具有很大优势,利用其灵活的波束控制和信号处理性能,能够摆脱传统阵列发射信号限制,灵活接收和处理复杂信号。通过发出窄带信号进而获得宽带信号探测参数,大大降低操作成本,实现高效率、高精度、高性价比三维立体成像。现如今埋体管线探测成为城市发展中不可避免的痛点,小埋藏体检测成像更是难点问题。文章提出一种基于多进多出技术(Multiple-Input Multiple-Output,简称MIMO)的频率分集阵列三维合成孔径雷达(3D-FDA-MAR)成像方法,并将MIMO阵列引入频率分集阵列实现三维成像,建立了MIMO-FDA三维形貌成像模型。该多进多出频率分集阵列在三维空间中能够随平台运动而运动,在沿航向处得到综合孔径,根据切航向阵列能够获得仿真频率分集阵列平面,从而得到目标物成像的三维立体效果,实现精准定位,全空间透视探测,智能3D成像,小埋藏体的精准检测诊断。

基于相控阵合成孔径的颅骨轮廓快速测量算法研究

作为一项新兴的神经调控技术,经颅聚焦超声技术目前广泛应用于脑深部的神经调控与治疗中。颅骨的异形和声参数的极大差异性是导致聚焦超声穿透颅骨后实际焦点的偏移和焦域散焦的主要原因。本研究以合成孔径技术为基础,由相控阵发射超声信号并接收于颅骨内外轮廓反射的回波信号,同时计算得到颅骨轮廓点坐标,实现对颅骨轮廓的快速测量。建立仿真模型,并利用颅骨仿体对算法进行仿真与实验验证。仿真结果表明,颅骨模型外轮廓中心区域的最大探测误差为0.15 mm,边缘区域为0.4 mm;内轮廓中心区域最大探测误差为0.3 mm,边缘区域为0.5 mm。实验结果表明:颅骨仿体外轮廓中心区域的最大探测误差为0.4 mm,边缘区域为0.8 mm;内轮廓中心区域最大探测误差为0.6 mm,边缘区域为0.9 mm。所设计的颅骨轮廓快速测量算法能够实现在2 min内完成颅骨内外轮廓的精确测量,并控制最大测量误差在1 mm以内。与核磁共振扫描(MRI)以及电子计算机断层成像(CT)相比,降低了治疗成本和治疗时间,同时为下一步调整相控阵阵元发射延时,实现在颅内的实时精确聚焦,提供了新的方法和思路。

用于InGaAs单光子探测器的微透镜阵列及表征

微透镜与探测器芯片的集成应用可以提高探测器的光能利用效率,从而提高探测器的灵敏度。针对两种InP基InGaAs单光子红外探测器,分别设计了材料为磷化镓和硅的两种方形孔径微透镜阵列。介绍了微透镜阵列结构参数的设计流程并分析了每个步骤的设计要点,利用光线追迹软件对设计的微透镜阵列结构参数进行仿真校核,确定了两种微透镜阵列符合设计要求。使用台阶仪和共聚焦显微镜对制作完成的两种微透镜阵列进行了形貌检测,计算得出两种微透镜阵列的曲率偏差分别为1.38%和3.44%。实验测试了1.064μm波长下两种微透镜阵列在空气中的焦距,与模拟结果对比,得到焦距偏差为5.69%和2.76%。通过分析微透镜的制作工艺,两种偏差符合应用需求。

基于浮空器照射源的双基弧形阵列SAR辅助降落模式成像算法

较之传统的单基线性阵列SAR,以浮空器为照射源平台的双基弧形阵列合成孔径雷达(Synthetic Aperture Radar,SAR)是一种全新高效、高分辨率的雷达成像系统;该成像模式继承了弧形阵列天线和浮空器的优点,在直升机辅助降落、应急救灾等领域具有重要的应用前景。在该成像模式中,由于浮空器平台平向移动、直升机平台向下运动以及弧形阵列天线特殊的圆弧型构造的影响,目标的回波信号很难直接处理,给成像带来了困难。针对这些问题,根据浮空器照射源双基弧形阵列SAR模式的成像几何模型以及回波特征,本文提出了一种基于两步运动补偿和Keystone变换的方法。其中第一步利用Taylor级数展开对双平台复杂斜距方程进行近似处理,对该成像模式下的距离分辨率和方位分辨率进行了简单分析,第二步根据浮空器平向运动产生的斜距误差,构造相应的运动补偿因子对浮空器平移引起的距离徙动项进行相位补偿;第三步根据直升机平台向下运动产生的斜距误差,构造相应的补偿因子对直升机下降引起的距离徙动项进行补偿;之后为了校正距离向与方位向之间耦合,根据Keystone变换思想引入新的角度变量对方位角进行变换从而补偿掉距离频率及方位向角度的耦合,接着在方位频域内进行方位向脉冲压缩。最后通过对不同点阵目标成像补偿前后的仿真结果对比分析、点阵目标成像性能指标分析以及场景分布目标的模拟验证了成像结果的准确性以及成像方法的有效性。

基于时间调制阵列的共孔径干扰辅助短包隐蔽通信

该文首次研究了基于时间调制阵列(TMA)的共孔径干扰辅助短包隐蔽通信。首先提出并设计了共口径干扰的TMA架构,提出一种优化方法,能够在最大化目标方向信号增益的同时对非目标方向形成干扰。基于上述模型,推导出隐蔽性约束和隐蔽吞吐量的闭合表达式。在此基础上,该文进一步对发送功率和数据包长进行联合优化,以最大化隐蔽吞吐量。仿真结果表明,存在一个使隐蔽吞吐量最大化的最优包长,所提方案相比基准方案实现了更好的隐蔽通信性能。

基于相控阵与合成孔径聚焦方法的CMUT阵列虚拟声源成像技术

对电容式微机械超声换能器(CMUT)阵列成像中的相控阵(PA)和合成孔径聚焦技术(SAFT)的综合方法进行研究,使用CMUT子阵列形成虚拟声源,并利用虚拟声源的辐射能量进行超声成像。通过对比不同孔径的超声波声束发散程度,得到CMUT阵列最佳子孔径阵元数量为9,CMUT阵列实验通过将子孔径阵元数量从1到15依次增加,观察水中两个不同深度的钉子成像清晰度来验证最佳子孔径阵元数量。与传统全矩阵捕捉(FMC)成像技术相比,多阵元SAFT合成的虚拟声源辐射能力更强,所以有更好的探测深度,同时由于利用子阵列进行超声数据采集,因此减少了CMUT超声成像系统的硬件采集通道数。

用于高功率微波系统的全介质透镜阵列天线

为了实现透镜阵列天线所需的移相范围,设计了两种不同的单元结构,通过优化参数,在保证良好的传输幅值的基础上实现相移范围的互补。为了探索在高功率微波系统应用,对两种单元的功率容量也开展了详细研究。在无限周期情况下,随着单元尺寸变化,单元功率容量范围为1.08~19.37 MW;通过研制口径为315 mm×315 mm的透镜天线来构建有限周期条件,并仿真计算得到该天线最大功率容量为226.553 MW,功率密度可以达到2283.23 W/mm^(2),并且该天线在中心频点10 GHz处峰值增益可达到29.37 dBi,口径效率为62.43%,副瓣电平约为-21.54 dBi。结果表明所提出单元的有效性与正确性,也说明设计的透镜阵列天线不仅具有良好的辐射特性,同时具有MW量级的功率容量。