The dipole moment of a circular loop carrying a current

The dipole moment of a circular loop carrying a current $\mathrm{I}$, is $\mathrm{m}$ and the magnetic field at the centre of the loop is $\mathrm{B}_{1}$. When the dipole moment is doubled by keeping the current constant, the magnetic field at the centre of the loop is $B_{2}$. The ratio $\frac{B_{1}}{B_{2}}$ is :