Complex sentence: The spectral response of the matched filter has a magnitude which is the mirror image of that of the expanded pulse, when a chirp spectrum has symmetry about its centre frequency, so the Fresnell ripples on the spectrum are augmented by the compression process.
Split into simpler sentences: The spectral response of the matched filter has a magnitude which is the mirror image of that of the expanded pulse. This is because a chirp spectrum has symmetry about its centre frequency, so the Fresnell ripples on the spectrum are augmented by the compression process.