7.2. 1 Windows function method o Let Ha(ejo denote the desired frequency response function o Since Ha(ejd)is a periodic function of o with a period 2n, it can be expressed as a Fourier serles, H(e)=∑h[l n=-007.2.1 Windows function method  Let Hd(ejω) denote the desired frequency response function.  Since Hd(ejω) is a periodic function of ω with a period 2π, it can be expressed as a Fourier series, ( )   j j d d n H e h n e    − =− = 