We explain the large scale correlations in radio polarization in terms of the correlations of galaxy cluster/supercluster magnetic field .
Assuming that the polarization correlations closely follow the spatial correlations of the background magnetic field we recover the magnetic field spectral index as -2.74 \pm 0.04 .
This remarkably agrees with cluster magnetic field spectral index obtained in cosmological magneto-hydrodynamic simulations .
We discuss possible physical scenarios in which the observed polarization alignment is plausible .