  In this letter, we investigate the robust and secure beamforming (RSBF) in an
intelligent reflecting surface (IRS) aided millimeter wave (mmWave) multiple
input single output (MISO) system, where multiple single antenna eavesdroppers
(Eves) are arbitrarily distributed nearby the legitimate receiver. Considering
the channel state information (CSI) of Eves' channels is imperfectly known at
the legitimate transmitter, the RSBF design problems to maximize the worst case
of achievable secrecy rate (ASR) are formulated under the total transmission
power and unit-modulus constraints. Since the problems are difficult to solve
optimally due to their nonconvexity and coupled variables, we substitute the
wiretap channels by a weighted combination of discrete samples and propose a
RSBF scheme based on alternating optimization and semidefinite relaxation (SDR)
techniques, for both colluding and noncolluding eavesdropping scenarios.
Simulation results show that the proposed RSBF scheme can effectively improve
the ASR and also outperforms other benchmark schemes.
