The properties of Bell number in proper order are studied with the use of elementary method, some identities involving the sum of product of Bell number in proper order are obtained.
利用初等方法研究了有序贝尔数的性质，给出了关于有序贝尔数的一组恒等式。
To product the sum and subtraction signals of the radar in a small volume, this paper introduces the method to realize the structure of a wideband planar magic-T.
为在小体积范围内产生雷达和信号、差信号，介绍了一种宽带平面型魔t结构的实现方法。
To product the sum and subtraction signals of the radar in a small volume, this paper introduces the method to realize the structure of a wideband planar magic-T.
为在小体积范围内产生雷达和信号、差信号，介绍了一种宽带平面型魔t结构的实现方法。
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