of decimated signal has four components. The first component is a frequency-stretched version of the input shown in fig he second, third and fourth components are shifted versions of first component, right shifted by 2π, 4π, and 6π respectively as shown in fig 10, 11 and 12.
It can be observed that the bandwidth π input spectrum is stretched to 4π (πx 4 = 4π) for decimation by 4 in each component of the spectrum decimated signal. Therefore, the frequency range of first component is stretched to -2π to +2π. Also, the magnitude of each component is scaled to 1/4 for decimation by 4.