共查询到19条相似文献,搜索用时 593 毫秒
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文章讨论了脉冲频率啁啾对用自相关法测量产生的误差,就脉冲的线性啁啾、二次啁
啾对测量结果的影响进行了理论分析和仿真计算。还提出了修正二次啁啾影响的简单方案,并结合实验测量结果进行了验证。 相似文献
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提出了一种双层电磁带隙(Electromagnetic Band Gap,EBG)结构,构建其电感电容(Inductance Capacitance,LC)等效电路并推算出双层EBG的谐振表达式,通过仿真软件对双层EBG结构上下两层的参数进行调节,分析各参数对电磁特性的影响规律,结果表明双层EBG可以产生两个零位相频率点,下层结构对应的零位相频率主要与下层的介质厚度及贴片大小有关,几乎不受上层的影响,而上层结构的谐振频率不仅与其自身参数有关也要考虑下层对其的影响,仿真结果与理论分析一致.该结构为EBG的具体设计和应用提供了指导依据. 相似文献
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机载短波通信是CNI(通信/导航/识别)体系内不可或缺的组成部分。运用短波通信理论分析了机载短波通信通信频率与通信距离之间的关系,鉴于通信距离在实战中的的重要性,提出了一种预测短波通信频率的方法。方法主要为以下2点:一、特定时间和路程下的最高可用频率;二、每一频率在每一时段的信噪比及可用性百分比。方法主要经由理论分析、软件辅助计算,并结合电磁环境的监测结果和实际地面互联互通经验对预测结果进行修正,给出每一时刻的最佳通信频率。最后,通过真实飞行试验对该方法的可行性进行了工程验证。 相似文献
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建筑物墙体对信号的衰减对于通信信号在城市环境中的传播影响很大,透射信号的衰减是影响通信质量的重要方面。文中采用自由空间法建立测试系统,在300M~3GHz的频率范围之间对不同建筑物墙体进行信号穿过墙体透射衰减的实地测量,通过加权的算法得到建筑物的等效介电常数。同时,通过在固定频率下透射波和空旷地接受信号场强的比较计算得到透射系数,利用上述的固定频率下透射系数和等效介电常数结合菲涅尔公式反演其该频率下的等效电导率,得出建筑物墙体等障碍物在不同频率下的等效电导率。利用基于时域有限差分差分法的XFDTD软件进行仿真计算,结果验证仿真结果和实际测量结果比较吻合。 相似文献
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在H面电感膜片波导带通滤波器的设计中,考虑到加工产生倒角及其产生的频率偏移,总结出带倒角膜片滤波器的精确设计方法,并给出了修正公式。为了验证本文提出的设计方法,利用HFSS对具有不同的中心频率、不同的3 dB带宽(BW)和不同的倒角半径下对这种滤波器进行了仿真,其中心频率分别为18 GHz,26 GHz,34 GHz和42 GHz,对应的带宽对应为2.265%,2.5%,10%,15%和20%,仿真结果表现出了规律性偏移趋势。通过对中心频率和带宽分别为26 GHz、2.5%和34 GHz、2.265%的2种H面波导滤波器进行实测,测试结果与利用修正公式的仿真结果一致。 相似文献
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Kuwabara N. Tajima K. Kobayashi R. Amemiya F. 《Electromagnetic Compatibility, IEEE Transactions on》1992,34(4):391-396
The sensitivity of an electromagnetic field sensor which uses a LiNbO3 electrooptical crystal and an optical-fiber link is improved by using a Mach-Zehnder interferometer, whose half-wave voltage is about 4 V at 1.3-μm wavelength, and a YAG laser pumped by a laser diode whose output power is 25 mW. The resulting frequency response is about flat from 100 Hz to 300 MHz, and the minimum detectable electric field strengths are 0.22 mV/m at 50 MHz and 0.079 mV/m at 750 MHz. The variation of the sensitivity with the frequency and element length are analyzed using the moment method, and the calculated results agree with the measured results. The measurement of the cross-polarization of the sensor indicates that this property is similar to that of a dipole antenna. The improved sensor can measure an electromagnetic impulse whose peak value is larger than 10 V/m and whose width is wider than 5 ns 相似文献
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利用渐近波形估计(AWE)技术分析了线面连接混合结构宽频带电磁特性。为了保证线面连接处电流的连续性,采用线-三角形模型,导体部分和导线部分与线面连接处分别采用不同的基函数;推导出线面连接混合结构的阻抗矩阵及其高阶导数,通过矩量法(MoM)求解线面积分方程得到给定频率点电流分布,然后应用AWE 技术快速有效地实现了导体和线结构在宽频带内的电流分布,得到整个线-面连接混合结构的输入阻抗和辐射方向
图,通过与MoM 结果相比,验证了该方法在分析线面混合结构宽带问题方面的高效性。 相似文献
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一种二维金属电磁带隙结构的电磁传输特性 总被引:2,自引:0,他引:2
采用时域有限差分法与Floquet定理相结合,对由正方形金属柱构成的二维电磁带隙结构的传输特性进行了分析和计算,得到了不同频率的平面电磁波在不同角度入射时,该结构的传输参数及电磁特性。通过改变金属方柱的边长和间距,得到了电磁带隙结构的阻带中心频率的变化规律,进而得到了拟合公式,该公式计算结果与仿真结果间最大误差不超过2%,具有较好的可靠性和较高精度,可用于EBG结构的应用研究。 相似文献
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This paper presents a new micro electromagnetic energy harvester that can convert transverse vibration energy to electrical power.It mainly consists of folded beams,a permanent magnet and copper planar coils.The calculated value of the natural frequency is 274 Hz and electromagnetic simulation shows that the magnetic flux density will decrease sharply with increasing space between the magnet and coils.A prototype has been fabricated using MEMS micromachining technology.The testing results show that at the resonant frequency of 242 Hz,the prototype can generate 0.55μW of maximal output power with peak-peak voltage of 28 m V for 0.5g(g = 9.8 m/s~2) external acceleration. 相似文献
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提出了一种三维实体重建技术与柱坐标抛物方程结合的城市环境电波传播预测方法。从数字地图
中提取城市建筑物高程矢量数据,建立立体光刻文件的拓扑数据结构,将其转化为抛物方程模型对应的扇形栅格数
据,实现城市建筑群的三维几何模型重构。同时结合聚类算法并利用城市影像信息对地表环境进行分类,对不同类
型的地表媒质赋予不同电磁参数,实现真实城市环境下同时包含建筑物信息和地表媒质参数的一体化电磁建模。
最后,采用分步傅里叶圆柱坐标系抛物方程法,对三维城市环境中电波的传播特性进行仿真分析。数值计算结果表
明,相较于传统经验模型,该方法能够考虑电波的反射、折射和衍射效应,可准确预测真实城市环境下的电波传播规
律,且具有较高计算效率。本模型可为无线网络规划、电磁频谱地图构建等提供指导。 相似文献
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J. Vales-Alonso F. J. González-Castaño J. P. Muñoz-Gea J. García-Haro L. Muñoz-Gutiérrez F. J. Gil-Castiñeira 《Wireless Personal Communications》2011,56(2):255-275
The effect of electromagnetic radiations from wireless cellular telephony systems on human health has been intensely discussed.
As a result, and despite the lack of evidence on any adverse effects, recent regulations make network planning even more difficult.
Base stations, even those covering urban areas, tend to be placed at suburban locations (in this paper we cite some examples
of related local regulations). In these cases, mobile stations inside urban locations must raise their power transmission
level to reach suburban antenna placements. Therefore, users may complain of a higher radio exposure. In this work we propose
a feasible solution to reduce electromagnetic activity from mobile communications equipment and to cope with restrictive placement
regulations. To accomplish this goal, a suburban base station is divided into an active part (transmitter) that is kept at the suburban location, and a passive part (receiver), which is moved inside the urban area. Thereby, the power received from the base station can be considered negligible inside
the urban area (since the active part is far away), and mobile terminal/stations transmit lower power levels (since passive
receivers are close to them). We justify the solution in the context of the globally available GSM networks, both analytically
and with empirical and simulation tests. The results in this paper reveal that our approach reduces electromagnetic levels
and improves uplink quality, which reaches typical levels of urban base stations. 相似文献
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An empirical propagation prediction model is described for mobile communications from high altitude platforms (HAPs) in different types of built-up areas. The model introduced here is defined as a function of the angle of elevation. The target frequencies are selected from the 2 to 6 GHz frequency band prospective for 3G and 4G mobile systems, namely at 2.0,3.5, and 5.5 GHz. This new HAP model recognizes two cases - line of sight (LOS) and non-line of sight (NLOS) between a HAP and a user at street level. The simulation of the urban environment is based on a statistical approach. Additional shadowing path loss is calculated using the uniform theory of diffraction for NLOS conditions. Normal distribution of the additional shadowing path loss was distinguishable from the simulation results. The shadowing path loss is defined as a function of the elevation angle. The results of the empirical model developed for idealized conditions are verified by measurements taken from a remote-controlled airship in different types of urban environment. Close correlation was achieved between the theoretical model and the experimental data. The HAP elevation dependent shadowing model is easy to implement and can be used for realistic planning and simulations of mobile networks provided via HAPs in built-up areas. 相似文献
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家用微波炉内磁控管的频率会有波动,且难以测定。为考查微波频率波动对样品温度分布的影响, 获得更加精确的仿真结果,研究假设家用微波炉的频率以2. 45 GHz 为中心波动,并对不同波动范围的频率(2.44~2.46 GHz,2.43~2.47 GHz,2.41~2.49 GHz)与单个频率(2.45 GHz)的基于有限元模型的仿真结果与实验结果进行了比较分析。实验对象是放置于微波炉内加热60 s 的土豆泥。对于不同的频率范围分布,每隔0. 005 GHz 计算一次电磁功率密度,并根据余弦分布对它们进行加权平均,最后将电磁功率作为热源加热土豆泥。模拟结果分别与用热成像仪和光纤热电偶测定的土豆泥表面温度分布和各部位瞬时温度的实验值进行比较。结果显示频率波动范围在2.44~2.46 GHz 预测的温度场与实验值有较好的一致性;而在2.41~2.49 GHz 范围内,温度分布的均匀性最好。该模型也可为指导微波食品的开发提供理论依据。 相似文献