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利用甚低频(VLF)传播相位的观测结果,证明了VLF传播C层效应的存在.基于C层效应产生原因,导出了包含C层效应的VLF传播相速时变函数和相位预测模型,并利用回归分析揭示了C层效应的日、季变化规律. 相似文献
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电离层电波传播相位污染校正 总被引:13,自引:7,他引:13
电离层电波传播相位污染使天波超视距雷达(OTHR)接收的回波信号谱扩展。采用合成孔径雷达(SAR)成像中的相位梯度算法(PGA)来校正相位污染,PGA算法要求所处理的各个分辨单元(这里包括方位和距离单元)具有相同的相位误差,但当对于电离怪空间变化剧烈,或OTHR距离和方位分辨率比较粗时,相邻单元的相位污染不完全相同,这里PGA方法不适用。针对这种情况,考虑相位变化不可能非常剧烈。可用低次多项式表示时,采用最小熵搜索方法,分别校正各单元的电离层相位污染。最后采用我国录取的OTHR实测数据验证,表明这两方法的校正效果良好。 相似文献
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于2010年7月13日至16日正午前后在挪威Troms地区(69.6°N)使用224MHz甚高频非相干散射雷达对极区夏季中层回波(PMSE)进行了观测.雷达几乎每天都捕捉到了PMSE现象,且其时常具有双层结构.为专门研究PMSE方向敏感性,采用了转动雷达发射波束指向的观测模式.对于13日的高PMSE层,回波功率随波束天顶角的增大而衰减,回波半宽角为8.9°.然而,对于13日的低PMSE层和14—15日的PMSE层,回波功率与波束指向基本无关,这与国际上早期使用约50MHz甚高频雷达观测的结果不一致. 相似文献
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甚低频对潜通信信号场强预测 总被引:1,自引:0,他引:1
甚低频(VLF)电波传播过程中因环境因素影响会使信号产生衰减与扰动,导致潜艇收信可靠性下降.文中基于传播媒质环境地-电离层参数的统计预测,运用波导模式理论对甚低频电波的信号场强进行预测,为甚低频对潜通信系统在运行中调整其可变参数或在特定参数条件下避开传播衰减与扰动提供传播环境服务,使通信系统工作性能与信道特性达到良好匹配,从而实现提高对潜通信效能的目的. 相似文献
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This paper describes a novel low-power wideband low-phase noise divide-by-two frequency divider.Hereby,a new D-latch topology is introduced.By means of conventional dynamic source-coupled logic techniques,the divider demonstrates a wideband with low phase noise by adding a switch transistor between the clock port and the couple node of the input NMOS pair in the D latch.The chip was fabricated in the 90-nm CMOS process of IBM.The measurement results show that the frequency divider has an input frequency range from 0.05 to 10 GHz and the phase noise is-159.8 dBc/Hz at 1 MHz offset from the carrier.Working at 10 GHz,the frequency divider dissipates a total power of 9.12 mW from a 1.2 V supply while occupying only 0.008 mm2 of the core die area. 相似文献
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通过对各种2分频器结构的研究,提出一种新结构的D触发器。由此触发器组成的2分频器具有宽带低相位噪声的特点。与传统的动态SCL结构的D触发器相比,通过在D触发器的输入对管的耦合端口和时钟端口之间加一个开关管,扩展了工作带宽并同时保持了低的相位噪声。此芯片采用IBM 的90nm CMOS工艺。测试结果表明,此2分频器工作的频率范围为:0.05-10GHz。工作频率为10GHz时,输出信号的相位噪声在频偏1MHz处为-159.8 dBc/Hz 。工作电压为1.2V,功耗为9.12mW。核心芯片面积仅为0.008mm2。 相似文献
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Yesim Hekim Niyazi Odabasioglu Osman N. Ucan 《International Journal of Communication Systems》2007,20(4):397-410
In this paper, in order to improve bit error performance, bandwidth efficiency and reduction of complexity compared to related schemes such as turbo codes, we combine low density parity check (LDPC) codes and continuous phase frequency shift keying (CPFSK) modulation and introduce a new scheme, called ‘low density parity check coded‐continuous phase frequency shift keying (LDPCC‐CPFSK)’. Since LDPC codes have very large Euclidean distance and use iterative decoding algorithms, they have high error correcting capacity and have very close performances to Shannon limit. In all communication systems, phase discontinuities of modulated signals result extra bandwidth requirements. Continuous phase modulation (CPM) is a powerful solution for this problem. Beside CPM provides good bandwidth efficiency; it also improves bit error performance with its memory unit. In our proposed scheme, LDPC and CPFSK, which is a special type of CPM, are considered together to improve both error performance and bandwidth efficiencies. We also obtain error performance curves of LDPCC‐CPFSK via computer simulations for both regular and irregular LDPC code. Simulation results are drawn for 4‐ary CPFSK, 8‐ary CPFSK and 16‐ary CPFSK over AWGN, Rician and Rayleigh fading channels for maximum 100 iterations, while the frame size is chosen as 504. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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针对电网广域测量信息含噪量较大、电网互联区域振荡阻尼难以控制的问题,以提升电网供电质量为目的,提出应用广域测量信息的低频低压解列装置自动化控制技术。以广域测量系统(WAMS)为基础,获取电网运行时的广域测量信息,利用小波分解去噪方法去除电网广域测量信息所含噪声后,通过基于Prony的电网低频振荡识别方法识别电网振荡区域与振荡数值;然后以电网振荡区域与振荡数值为基础,计算振荡中心电压和定位系数,并将其作为输入,设计低频低压解列装置自动化控制流程,实现低频低压解列装置自动化控制。实验结果表明,该方法可有效去除电网广域测量信息内所含噪声,电网互联区域振荡阻尼数值最大误差值仅为0.01,且可有效地控制低频低压解列装置。 相似文献
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Besides the electrode-pair antenna,the magnetic antenna is also used for the extremely low frequency (ELF) submarine communication.To receive the weak ELF signals,the structure of a small sized magnetic antenna determines its specific electrical characteristics.The ELF magnetic antenna shows high internal resistance, alternating-current impedance,and a resonance frequency near the operating bandwidth.In accordance with the electrical characteristics of ELF magnetic antenna,a low noise preamplifier and frequency compensation circuit were designed and realized.The preamplifier is a three-stage negative feedback circuit,which is composed of parallel JFET,common-emitter amplifier with a Darlington structure and a common-collector amplifier in push-pull connection.And a frequency compensation circuit is cascaded to compensate the characteristic in low frequency range.In the operating bandwidth f = 30-200 Hz,the circuit has a gain of 39.4 dB.The equivalent input noise is 1.97 nV/Hz1/2 and the frequency response keeps flat in operating bandwidth.The proposed preamplifier of the ELF magnetic antenna performs well in receiving ELF signals. 相似文献
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简要介绍毫米波频率合成器的重要性,分析两种毫米波频率合成器实现方案的优劣,综合其优点,并采用直接数字频率合成(DDS)技术,提出毫米波频率合成器的设计方案。进行方案系统实验,结果表明,相位噪声为-85dBc/Hz@10kHz,提升了整个毫米波通信系统的性能。 相似文献
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