共查询到10条相似文献,搜索用时 125 毫秒
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A modified sampling technique is applied to the reconstruction of the antenna far-field pattern from near-field measurements on a cylinder. It is shown that, if a proper phase factor is singled out from the tangential components of the measured electric field, the samples spacing along the axis of the measurement cylinder increases linearly with the cylinder radius. Thus, when this radius is substantially larger than the antenna's dimension, the sample's spacing can be much greater than the half-wavelength spacing commonly accepted as the maximum possible one, without losing the computational efficiency of the standard approach 相似文献
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K. Doverspike L. B. Rowland D. K. Gaskill J. A. Freitas 《Journal of Electronic Materials》1995,24(4):269-273
This paper presents a comparative study of the properties of GaN grown by organometallic vapor phase epitaxy, using both a
GaN and A1N buffer layer, as a function of sapphire orientation (c-plane vs a-plane). Results are presented for varying the
thickness of the buffer layer, varying the growth temperature of the GaN film, and also varying the ammonia/trimethylgallium
mass flow ratio. The electron Hall mobilities of GaN films grown on an A1N buffer layer were, in general, higher compared
to films grown using a GaN buffer layer. In addition, growth on a-plane sapphire resulted in higher quality films (over a
wider range of buffer thicknesses) than growth on c-plane sapphire. The room temperature electron mobilities were also found
to be dependent on, not only the growth temperature, but also the ammonia/trimethylgallium mass flow ratio. 相似文献
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提出了数字投影的填充因子对相位测量的误差分析。在结构光三维测量中,数字投影容易改变条纹周期和产生准确的相移,因而到了越来越广泛的应用。然而相比传统的机械模拟投影方式,数字投影采用了抽样方式,且由于其自身结构的限制,填充因子不能做到100%,必然对相位测量有影响。针对填充因子对相位测量的误差,还没有人进行充分研究。对填充因子引起误差原因进行分析,并给出其数学描述,从而建立了理论依据,还进一步提出了离焦减少误差的方法,并给出了其数学表达。最后通过模拟实验的方法,对理论进行了验证,实验结果证明了填充因子减少将增大测量误差,离焦法可以减少相位测量误差。 相似文献
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该文主要阐述了一种利用全相位FFT变换、快速浮点数除法、非均匀量化查表的方法。来完成三相电伏安相位测量算法的设计。全相位FFT的算法是先对数据进行全相位预处理,然后进行传统的确FFT运算。此算法具有初始相位不变和有效防止频谱泄露的特性,很好地解决非同步采样的频谱校正问题。 相似文献
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为了分析射频直接采样系统中的等效相位噪声模型,文中给出了射频直接采样接收机的简化构架,然后理论推导了射频直接采样接收机采样输出信噪比与采样时钟之间的关系表达式。最后,通过建立仿真实验平台对推导结论进行了实验验证,结果表明:射频直接采样系统对采样时钟的频谱纯度要求高,采样输出的信噪比和无杂散动态范围会在时钟信号频谱的基础上恶化。射频直接采样系统可视为射频本振混频和量化采样的过程,其等效相位噪声模型与常规超外差式接收机是一致的。 相似文献
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