  We prove that two n-by-n matrices A and B have their rank-k numerical ranges
$\Lambda_k(A)$ and $\Lambda_k(B)$ equal to each other for all k, $1\le k\le
\lfloor n/2\rfloor+1$, if and only if their Kippenhahn polynomials
$p_A(x,y,z)\equiv\det(x Re A+y Im A+zI_n)$ and $p_B(x,y,z)\equiv\det(x Re B+y
Im B+zI_n)$ coincide. The main tools for the proof are the Li-Sze
characterization of higher-rank numerical ranges, Weyl's perturbation theorem
for eigenvalues of Hermitian matrices and Bezout's theorem for the number of
common zeros for two homogeneous polynomials.
