Antenna Array Design for Directional Modulation

Abstract

Directional modulation (DM) as a physical layer security technique to keep known constellation points in the desired directions, while making the points scrambled in other directions has been achieved. DM is normally applied on uniform linear arrays (ULAs) where the maximum spacing between adjacent antennas is a half wavelength of the frequency of interest in order to avoid spatial aliasing. In this thesis, to have a larger aperture and a higher spatial resolution given a fixed number of antennas, compressive sensing (CS) based sparse antenna array design for DM is formulated. Two practical scenarios are considered in the proposed design: robust design with model errors, and design with practical non-zero-sized antennas. To extend the frequency spectrum, multi-carrier based phased antenna array design for DM by using Inverse Discrete Fourier Transform (IDFT) is introduced. The modified Wideband Beampattern Formation via Iterative Techniques (modified WBFIT) method is proposed to reduce the peak to average power ratio (PAPR) to a given threshold for a given antenna array geometry. Moreover, polarisation states of signals are exploited on crossed-dipole array for DM to further increase the channel capacity. Based on a multi-path model, positional modulation design is proposed to make sure that only in desired locations the received signal can be recovered successfully, while in the positions around, the received modulation patterns are scrambled.