Orthogonally polarised dual-channel directional modulation based on crossed-dipole arrays

Directional modulation (DM) as a physical layer security technique has been studied based on traditional antenna arrays; however, in most of the designs, only one signal is transmitted at one carrier frequency. In this paper, signal polarisation information is exploited, and a new DM scheme is designed which can transmit a pair of orthogonal polarised signals to the same direction at the same frequency simultaneously, resulting in doubled channel capacity. These two signals can also be considered as one composite signal using a four dimensional (4-D) modulation scheme across the two polarisation diversity channels. Moreover, compressive sensing (CS) based formulations for designing sparse crossed-dipole arrays in this context are proposed to exploit the degrees of freedom in the spatial domain for further improved performance, as demonstrated by various design examples.