共查询到17条相似文献,搜索用时 250 毫秒
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针对标准的差分进化算法只能处理连续空间的优化问题,提出了一种基于取整策略的差分进化算法。该方法只需要对优化变量进行四舍五入取整,就能够把标准差分进化算法用于稀疏阵列天线方向图优化。将取整策略的差分进化算法应用到六边形平面稀疏天线阵的布阵设计。为了计算六边形阵列天线的方向图,提出在口径中添加虚拟单元的计算模型,把六边形阵列转化为可以实现二维快速傅里叶变换的矩形阵列。以改善阵列峰值副瓣电平为目的进行仿真试验,结果表明,优化后的稀疏天线阵峰值旁瓣电平与采用遗传算法相比改善了4.5~5.1 dB,且具有计算速度快、稳定性好的优点。 相似文献
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设计并实现了一种V频段圆柱龙伯透镜天线。在平行平板波导间,根据龙伯透镜原理与介电常数等效原理,推导出了圆柱龙伯透镜天线的理论设计公式,并结合商业仿真软件高频结构仿真器(HFSS)仿真分析和优化,完成天线设计。仿真结果表明,该V频段圆柱龙伯透镜天线增益为21.4 dBi,波束宽度为1.56°,副瓣电平为-14.7 dB。根据设计结果,加工和测试验证V频段圆柱龙伯透镜天线的可实现性,实测结果表明,该天线增益为20.1 dBi,波束宽度为1.60°,副瓣电平为-11.1 dB,天线效率为45.7%,说明该天线具有一定的工程应用价值。 相似文献
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针对毫米波平板裂缝阵天线加工难度大的特点,采用优化总体设计、精确提取耦合缝阻抗数据和详细的公差分析等措施精确设计天线参数,对关键尺寸进行严格控制的同时尽量放宽其它加工公差,降低加工难度.提出的和差器缝隙匹配技术,大大减少了加工量、减小了加工难度和改善了折叠魔T工作带宽.首次加工的样机电性能优良,测试结果与理论吻合良好,和路驻波小于2的带宽达2.3 GHz,天线的方位副瓣电平达到-23 dB,俯仰副瓣电平达到-25 dB. 相似文献
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针对小孔径超视距目标探测时阵列孔径减小空域滤波性能下降的问题,提出了一种正交频分非线性调频(OFD-NLFM)的发射波形设计方法。首先以正切调频函数为频率函数对发射信号进行建模,详细说明了影响脉压性能的正切函数时间副瓣电平控制因子的选择方法,重点提出一种基于凸优化的脉压信号峰值旁瓣抑制算法,建立了脉压输出噪声功率最小的优化模型并进行求解。仿真表明,提出的正交频分非线性调频信号具有较好的正交性,采用凸优化加权算法后脉压主瓣宽度比传统线性调频信号降低约1/3,峰值旁瓣为-31.22 dB,旁瓣电平平均值小于-100 dB,具备更低的抗噪声和干扰性能,从波形设计和脉压处理角度改善了空域滤波性能的不足。 相似文献
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GPS卫星接收机的自适应抗干扰设计 总被引:1,自引:0,他引:1
提出了一种加强GPS卫星接收机抗干扰能力的技术实现方案,采用自适应调零技术以及天线阵的具体实现方式来消除干扰。文中还对自适应天线阵所采用的功率倒置的算法做了详细说明,并进行了计算机仿真。 相似文献
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Y. Maghsoodi 《Mathematical Finance》2007,17(2):249-265
Exact explicit solution of the log-normal stochastic volatility (SV) option model has remained an open problem for two decades. In this paper, I consider the case where the risk-neutral measure induces a martingale volatility process, and derive an exact explicit solution to this unsolved problem which is also free from any inverse transforms. A representation of the asset price shows that its distribution depends on that of two random variables, the terminal SV as well as the time average of future stochastic variances. Probabilistic methods, using the author's previous results on stochastic time changes, and a Laplace–Girsanov Transform technique are applied to produce exact explicit probability distributions and option price formula. The formulae reveal interesting interplay of forces between the two random variables through the correlation coefficient. When the correlation is set to zero, the first random variable is eliminated and the option formula gives the exact formula for the limit of the Taylor series in Hull and White's (1987) approximation. The SV futures option model, comparative statics, price comparisons, the Greeks and practical and empirical implementation and evaluation results are also presented. A PC application was developed to fit the SV models to current market prices, and calculate other option prices, and their Greeks and implied volatilities (IVs) based on the results of this paper. This paper also provides a solution to the option implied volatility problem, as the empirical studies show that, the SV model can reproduce market prices, better than Black–Scholes and Black-76 by up to 2918%, and its IV curve can reproduce that of market prices very closely, by up to within its 0.37%. 相似文献
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In markets where dealers play a central role, bid-ask spreads inhibit asset valuation as defined by the formation cost of a replicating portfolio. We introduce a nonlinear valuation formula similar to the usual expectation with respect to the risk-adjusted probability measure. This formula expresses the asset's selling and buying prices set by dealers as the Choquet integrals of their random payoffs We investigate several price puzzles: the violation of the put-call parity and the fact that the components of a security can sell at a premium to the underlying security (primes and scores). 相似文献
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In this paper, we propose a new explicit series expansion formula for the price of an arithmetic Asian option under the Black–Scholes model and Merton's jump-diffusion model. The method is based on an equivalence in law relation together with the diffusion operator integral method proposed by Heath and Platen. The method yields explicit series expansion formula for the Asian options' prices. The theoretical convergence of the expansion to the true value is established. We also consider the American Asian option (i.e., Amerasian option) and derive the corresponding expansion formula through the early exercise premium representation. Numerical results illustrate the accuracy and efficiency of the method as compared with benchmarks in the literature. 相似文献
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In this paper, we build a bridge between different reduced‐form approaches to pricing defaultable claims. In particular, we show how the well‐known formulas by Duffie, Schroder, and Skiadas and by Elliott, Jeanblanc, and Yor are related. Moreover, in the spirit of Collin Dufresne, Hugonnier, and Goldstein, we propose a simple pricing formula under an equivalent change of measure. Two processes will play a central role: the hazard process and the martingale hazard process attached to a default time. The crucial step is to understand the difference between them, which has been an open question in the literature so far. We show that pseudo‐stopping times appear as the most general class of random times for which these two processes are equal. We also show that these two processes always differ when τ is an honest time, providing an explicit expression for the difference. Eventually we provide a solution to another open problem: we show that if τ is an arbitrary random (default) time such that its Azéma's supermartingale is continuous, then τ avoids stopping times. 相似文献