  We provide a recurrent construction of entanglement witnesses for a bipartite
systems living in a Hilbert space corresponding to $2N$ qubits ($N$ qubits in
each subsystem). Our construction provides a new method of generalization of
the Robertson map that naturally meshes with $2N$ qubit systems, i.e., its
structure respects the $2^{2N}$ growth of the state space. We prove that for
$N>1$ these witnesses are indecomposable and optimal. As a byproduct we provide
a new family of PPT (Positive Partial Transpose) entangled states.
