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1、信号表达式信号表达式幅频幅频相频相频1-31-3单边指数信号单边指数信号Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd. f(t)t0004.4非周期信号的频谱非周期信号的频谱Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.1-4 1-4
2、阶跃信号阶跃信号u u（t t）可表示）可表示 阶跃信号在跳变点阶跃信号在跳变点t=0t=0处，函数值未定义，或在处，函数值未定义，或在t=0t=0处定处定 。 幅值幅值A=1A=1的阶跃信号称为单位阶跃信号，表示为的阶跃信号称为单位阶跃信号，表示为u(t)10单位阶跃信号单位阶跃信号tEvaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd. 由于单位阶跃信号不满足绝对由于单位阶跃信号不满足绝对可积条件，不能直接由定义给出其
3、频谱，可积条件，不能直接由定义给出其频谱，可把它看成当可把它看成当 时的指数信号时的指数信号 在时域上的极限，其频谱为在时域上的极限，其频谱为 的频的频谱在谱在 时的极限。时的极限。 单边指数信号在时域上可表示为单边指数信号在时域上可表示为Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.其傅立叶变换为：其傅立叶变换为：其幅度谱、相位谱分别为其幅度谱、相位谱分别为 单边指数信号与频谱单边指数信号与频谱x（t）t0t00
4、Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.阶跃信号的频谱为阶跃信号的频谱为Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.符号函数Evaluation only.Created with Aspose.Slides for .NET
5、3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd. f1(t)10tSgn(t)+1-14.4非周期信号的频谱非周期信号的频谱Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.求被矩形窗函数截断的余弦函数 的频谱，并作频谱图。 Evaluation only.Created with Aspose.Slides for .NET 3.5 Clie
6、nt Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.方法一：按傅立叶变换的性质截断的余弦函数可以看成为：余弦函数与矩形窗 的点积，即： Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.根据卷积定理，其傅里叶变换为：Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.
7、0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.方法二：按傅立叶变换的定义Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Crea
8、ted with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.方法3Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.
