分别用矩形窗、汉宁窗、海明窗、三角窗和Blackman窗设计一 的线性相位带通滤波器，观察它们的3dB和20dB带宽，并比较五种窗的特点。-Respectively rectangular window, Hanning, Hamming window, triangular window and Blackman window design a linear phase bandpass filter, observe their 3dB and 20dB bandwidth and comp