周期信号是定义在区间内，按一定时间间隔（周期）不断重复的信号。设有周期信号，周期为，角频率，且满足狄里赫利条件，则该周期信号可以展开成傅立叶级数，即可表示为一系列不同频率的正弦或复指数信号之和。傅立叶级数有三角形式和指数形式两种

-Periodic signal is defined in the interval, by a certain time interval (cycle) repeated signal. With periodic signal, cycle, angular frequency, and satisfy the Dirichlet conditions, the periodic signal can be launched into a Fourier series can be expressed as a series of different frequencies of sinusoidal or complex exponential signal and. Fourier series has the triangular form and the form of two index