  While traditional electromagnetic stealth materials/metasurfaces can render a
target virtually invisible to some extent, they lack flexibility and
adaptability, and can only operate within a limited frequency and
angle/direction range, making it challenging to ensure the expected stealth
performance. In view of this, we propose in this paper a new intelligent
reflecting surface (IRS)-aided electromagnetic stealth system mounted on
targets to evade radar detection, by utilizing the tunable passive reflecting
elements of IRS to achieve flexible and adaptive electromagnetic stealth in a
cost-effective manner. Specifically, we optimize the IRS's reflection at the
target to minimize the sum received signal power of all adversary radars. We
first address the IRS's reflection optimization problem using the Lagrange
multiplier method and derive a semi-closed-form optimal solution for the
single-radar setup, which is then generalized to the multi-radar case. To meet
real-time processing requirements, we further propose low-complexity
closed-form solutions based on the reverse alignment/cancellation and minimum
mean-square error (MMSE) criteria for the single-radar and multi-radar cases,
respectively. Additionally, we propose practical low-complexity estimation
schemes at the target to acquire angle-of-arrival (AoA) and/or path gain
information via a small number of receive sensing devices. Simulation results
validate the performance advantages of our proposed IRS-aided electromagnetic
stealth system with the proposed IRS reflection designs.
