  A multiple-input single-output (MISO) wiretap channel model is considered,
that includes a multi-antenna transmitter, a single-antenna legitimate receiver
and a single-antenna eavesdropper. For the scenario in which spherical
uncertainty for both the legitimate and the eavesdropper channels is included,
the problem of finding the optimal input covariance that maximizes the
worst-case secrecy rate subject to a power constraint, is considered, and an
explicit expression for the maximum worst-case secrecy rate is provided.
