2. 2. 4 Frequency representation of periodic signals The Fourier series expression of the square wave sIgnal x(t)=-(siot+si300t+-sn5001+…) A 7a0 na Fig. 2. 12 Frequency spectrum of periodic square wave signalThe Fourier series expression of the square wave signal 2.2.4 Frequency representation of periodic signals sin 5 ) 5 1 sin 3 3 1 (sin 4 ( ) x t = 0 t + 0 t + 0 t +  Fig. 2.12 Frequency spectrum of periodic square wave signal