镜像频率抑制度对射频前端噪声系数的影响分析
Influence of Image Frequency Rejection on RF Front-End Noise Figure
  
DOI:
中文关键词:  射频前端,二次变频,噪声系数,镜频抑制,镜频抑制滤波器
英文关键词:RF front-end, secondary frequency conversion, noise figure, image frequency rejection, image frequency rejection filter
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徐 辉,李 兵,李拴涛 中国空间技术研究院西安分院, 西安 710071 
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中文摘要:
      探讨了镜频抑制度对于射频前端噪声系数的影响,分析计算了一次变频系统中有镜频抑制滤波器和镜频抑制滤波器两种情况下射频前端输出的噪声功率值,分析表明镜频抑制滤波器在一次变频系统中能够改善系统噪声系数约3 dB;针对二次变频系统射频前端的输出噪声功率,分析计算表明当镜频抑制度达到20 dB 以上时,镜像频率对射频前端输出噪声的影响很小,近乎可以忽略。给出一种Ka频段二次变频射频前端的实例,测试结果与理论分析一致。
英文摘要:
      In this paper, the influence of the image frequency rejection on the noise figure of the RF front-end is analyzed. The noise powers in primary down conversion system with or without image frequency rejection are calculated. It is shown that the image frequency rejection can improve the noise figure of the system by about 3 dB in the primary frequency conversion system. For the output noise power of RF front-end, the calculation shows that when the image rejection reaches 20 dB or more, the output noise is very small, almost negligible. An example of Ka-band secondary frequency conversion RF front-end is presented. The test results are consistent with the theoretical analysis.
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