Directional Modulation Based on Pattern-Diversity Holographic Metasurfaces

This paper proposes a novel physical-layer secure communication method using holographic metasurfaces (HM). By exciting different feeding ports, the HM can generate either a directional beam or a conical beam. The directional beam is used to transmit information, while the conical beam is employed to emit artificial noise (AN). Consequently, only legitimate users in the desired direction can correctly decode the information, whereas eavesdroppers in other directions are prevented from intercepting the information due to the AN interference effects. To validate the proposed secure communication method, two HMs, i.e., a scalar holographic metasurface (SHM) and a tensor holographic metasurface (THM) are designed. Two HM prototypes are fabricated and measured. The gain of the directional beams achieves 16.9 dBi, and the gain difference between directional beams and conical beams exceeds 21 dB at the intended broadside direction. Communication experiments demonstrate that the transmitted constellation points remain stable at 0o direction, while becoming noise-disrupted in other directions, effectively ensuring communication security.