A low profile dual band resonant cavity antenna

A low profile dual band resonant cavity antenna that incorporates double sided partially reflective surface (PRS) with complementary layers is presented here. The PRS is formed by printing periodic array of complementary metallic square loops on the opposite sides of the dielectric material. The PRS has been used as a superstrate, placed above the radiating microstrip patch. This PRS acts as a dual band matching section between the microstrip patch and free space, hence resulting in dual resonance. The proposed structure has been analyzed using equivalent circuit model. Parametric analysis of the sensitive structural parameters has also been discussed. To validate the design, the simulation analysis and experimental results obtained from a prototype operating at 8.9 and 9.4 GHz are presented. The measured gain at the two frequencies is 10.2 and 8.5 dBi, respectively. The overall size of the antenna is 1.78λ × 1.78λ × 0.09 λ with λ corresponding to 8.9 GHz.     

High performance resonant cavity antenna with non‐uniform metamaterial inspired superstrate

The resonant cavity antenna (RCA) is a class of widely used high gain antennas, but usually suffers from narrow impedance bandwidth owing to its strong resonant property, as well as relatively low aperture efficiency because of its non‐uniform electromagnetic (EM) field distribution on the aperture. This article explores enhancing the RCA's impedance bandwidth and aperture efficiency by designing a non‐uniform metamaterial inspired superstrate, on which the metal patches vary their sizes with respect to their distances to the superstrate's center. After optimized by the Genetic Algorithm, the proposed RCA is designed, fabricated and tested. Measured results agree well with simulated ones and show that in comparison with a RCA with a uniform metamaterial inspired superstrate, this work significantly improves the |S ₁₁| < ?10 dB impedance bandwidth from 2.1% to 6.1%, the gain at the working frequency 10 GHz from 19.07 dBi to 20.55 dBi, and correspondingly the aperture efficiency from 50.5% to 71%. A further analysis estimates that due to the non‐uniform metamaterial inspired superstrate, a more homogeneous distribution for both the amplitude and phase of the EM field is observed on the superstrate's aperture.     

Coaxial cavity waveguide antennas excited by stacked circular microstrip patches for use as prime‐focus reflector feeds

A coaxial cavity antenna excited by a stacked circular microstrip antenna is investigated as a feed for prime‐focus parabolic reflector antennas. The radiation pattern of the proposed cavity‐backed antenna is saddle shaped, which widens the ?10 dB beamwidths and increases the reflector efficiency especially for deep reflectors with small focal length‐to‐diameter ratios. With a single‐probe feed, the co‐polar radiation pattern is slightly asymmetric in the E‐plane, but is made symmetric by a differential feeding technique, using two probes. The impedance bandwidth of the proposed feed antenna is 20%. The antenna was fabricated and tested, and it exhibited good agreement between simulation and measurement results. The gain factor of the feed was also studied with a circular‐symmetric reflector and provided a gain factor of 79% at f/D = 0.375. This type of feed can be used as an alternative to conventional horn or waveguide feeds, where reduced size and light‐weight are desirable with added advantage of easy integration with electronics.     

水下航行体垂直发射尾部空泡形态与压力预示方法研究

水下航行体垂直发射尾部空泡形态与压力准确预示是航行体轴向速度设计的重要依据。该文基于对尾空泡形态发展演变的基本规律的认识,结合空泡独立膨胀原理和Rayleigh-Plesset方程,建立了尾空泡非定常发展数学模型,形成了尾空泡形态和压力的理论预示方法,并通过与试验数据的比对,验证了方法的合理性和可用性。此外,还研究了航行体出筒速度、阻力系数、尾空泡初始压力和燃气指数等影响要素对尾空泡压力和形态的影响。     

Ku波段多频高增益天线研究

针对传统平板天线频带单一,增益不高,方向性差等缺点,本文将电磁波的增强透射特性研究应用到天线的设计中,结合类f-p腔原理,设计了一款具有双频带、高增益的波导缝隙天线。天线在中心频率10.9 GHz和13.7 GHz的增益分别达到了10.8 dB和11.4 dB,并且相对于传统单缝波导天线,天线在中心频率点处E面的半波功率波束宽度分别减小了114°和90°。仿真结果和实测结果吻合度较高,尤其频带处于在Ku波段,在卫星雷达领域具有很大的应用价值。     

电磁脉冲与开孔腔内PCB板级MSL间的耦合研究

因PCB上微带线(MSL)与外界电磁能量耦合而生成感应电流(Current),会对敏感器件造成耦合伤害。而目前对此研究的关注度不够,故以带拐角MSL的PCB板内置于开孔屏蔽腔为研究对象,以Current计算为主要切入点,进行多参数耦合特性计算。先建立相应数值模型并验证建模方法有效性后,外置平面波激励源,利用有限元法考察不同计算位置、有无屏蔽腔、MSL夹角大小及拐角补偿等参数变化对电流的影响。结果表明：直MSL上不同计算位置对Current影响不大,其数值都要比MSL弯折时要大,两者差值随频率增加而逐渐减小;谐振点处腔体抑制效果会被弱化甚至完全失效;MSL与电场E平行放置时,迹线需布成短线,MSL与电场E垂直放置时,迹线可布成长线;MSL宽度增加,电流数值会增加但趋势减缓。拐角补偿方法对提高信号完整性(SI)有效,但对降低电磁耦合作用有限。不会影响谐振点出现位置是上述多参数研究的共性结果。     

基于箱体法材料电磁脉冲场屏蔽效能测试研究

为准确评价屏蔽材料在强电磁脉冲环境中的屏蔽效能,提出了一种基于屏蔽暗箱窗口法的材料电磁脉冲屏蔽效能时域测量方法。该方法将带有测试窗口的屏蔽箱体置于GTEM 室内,被测屏蔽材料安装在屏蔽箱的测试窗口上,利用置于腔体中心的单极子天线测量耦合进腔体的电磁脉冲电压波形,对测得的时域电压信号进行快速傅里叶变换( FFT) ,得到了被测材料频域屏蔽效能曲线。与频域测试结果进行了对比,结果基本一致。实验表明该测试系统可以有效减小局部增强效应对测量精度的影响,能够可靠评价强电磁脉冲作用下材料的屏蔽效能。     

Solution‐Processed Low Threshold Vertical Cavity Surface Emitting Lasers from All‐Inorganic Perovskite Nanocrystals

Recently, newly engineered all‐inorganic cesium lead halide perovskite nanocrystals (IPNCs) (CsPbX₃, X = Cl, Br, I) are discovered to possess superior optical gain properties appealing for solution‐processed cost‐effective lasers. Yet, the potential of such materials has not been exploited for practical laser devices, rendering the prospect as laser media elusive. Herein, the challenging but practically desirable vertical cavity surface emitting lasers (VCSELs) based on the CsPbX₃ IPNCs, featuring low threshold (9 µJ cm^?2), directional output (beam divergence of ≈3.6°), and favorable stability, are realized for the first time. Notably, the lasing wavelength can be tuned across the red, green, and blue region maintaining comparable thresholds, which is promising in developing single‐source‐pumped full‐color visible lasers. It is fully demonstrated that the characteristics of the VCSELs can be versatilely engineered by independent adjustment of the cavity and solution‐processable nanocrystals. The results unambiguously reveal the feasibility of the emerging CsPbX₃ IPNCs as practical laser media and represent a significant leap toward CsPbX₃ IPNC‐based laser devices.     

飞秒刻写光纤F P腔级联FBG传感特性研究

提出了一种飞秒刻写光纤法布里-珀罗(F-P)腔级联切趾布拉格光纤光栅(FBG)的微结构传感器并研究了该传感器的温度与应变传感特性。该微结构传感器光谱稳定性良好,监测时长2 h内FBG波长最大漂移量为0.009 nm,功率最大漂移量为0.015 d B,F-P腔波长最大漂移量为0.018 nm,功率最大漂移量为0.072 d B。当应变由0με增至450με再减回0με时,该微传感器FBG特征峰先右移再左移,波长变化0.530 4 nm,应变灵敏度约1.17 pm/με,线性度高于0.99;光纤F-P腔特征谷波长变化0.491 1 nm,应变灵敏度约1.10 pm/με,线性度高于0.90。当温度由50℃升至200℃再降回50℃时,FBG特征峰先右移再左移,波长变化约1.418 nm,应变灵敏度约10.09 pm/℃,线性度高于0.95;光纤F-P腔特征谷波长变化约1.578 nm,应变灵敏度约10.53 pm/℃,线性度高于0.98。所提出的微结构传感器是解决单根光纤双参数测量的有效手段,同时对复杂环境下的多参数耦合测量与解耦也具有重要的参考价值。     

基于Unwedge程序的地下洞室围岩力学参数敏感性分析

以某导流隧洞为工程背景,运用Unwedge程序以关键块体的重量为目标,对比优选出设计开挖隧洞的合理洞室走向和开挖断面型式,并以左边墙6号块体为研究对象,关键块体的安全系数作为评价指标,对拟定的6个影响块体围岩稳定的力学参数进行敏感性分析,得到黏聚力Sc的敏感度最高,其敏感度为0.922,对工程稳定性影响最大,内摩擦角Sf敏感度最低,敏感度为0.002,对工程稳定性影响最小。因此,通过围岩力学参数敏感性计算可为勘察设计人员合理确定参数值精度提供依据。