  As the excellent tools for aiding communication,intelligent reflecting
surface (IRS) and unmanned aerial vehicle (UAV) can extend the coverage area,
remove blind area, and achieve a dramatic rate improvement. In this paper, we
improve the secrecy rate (SR) performance at directional modulation (DM)
networks using IRS and UAV in combination. To fully explore the benefits of IRS
and UAV, two efficient methods are proposed to enhance SR performance. The
first approach computes the confidential message (CM) beamforming vector by
maximizing the SR, and the signal-to-leakage-noise ratio (SLNR) method is used
to optimize the IRS phase shift matrix, which is called Max-SR-SLNR. Here, Eve
is maximally interfered by transmitting artificial noise (AN) along the direct
path and null-space projection (NSP) on the remaining two channels. To reduce
the computational complexity, the CM, AN beamforming and IRS phase shift design
are independently designed in the following methods. The CM beamforming vector
is constructed based on maximum ratio transmission (MRT) criteria along the
channel from Alice-to-IRS, and phase shift matrix of IRS is directly given by
phase alignment (PA) method. This method is called MRT-NSP-PA. Simulation
results show that the SR performance of the Max-SR-SLNR method outperforms the
MRT-NSP-PA method in the cases of small-scale and medium-scale IRSs, and the
latter approaches the former in performance as IRS tends to lager-scale.
