Two identical wires $\text{A}$ and $\text{B}$, each of length ' $l$ ', carry the same current $I$ . Wire $\text{A}$ is bent into a circle of radius $\mathit{\text{R}}$ and wire $\text{B}$ is bent to form a square of side '$\mathit{\text{a}}$'. If $B_{\mathrm{A}}$ and $B_{\mathrm{B}}$ are the values of magnetic field at the centres of the circle and square respectively, then the ratio $\frac{B_{\mathrm{A}}}{B_{\mathrm{B}}}$ is