Security-Enhanced Directional Modulation Symbol Synthesis Using High Efficiency Time-Modulated Arrays.

Time-modulated arrays (TMAs) have been found useful to construct directional modulation (DM) transmitters, offering physical-layer security. Two issues, however, exist in conventional TMA DM, which are high power loss and generation of mirror harmonic frequency signals that may compromise wireless security. In this article, we propose to construct DM transmitters using a high efficiency TMA. By carefully designing the time sequences of the selected phase shifters, the DM symbols modulated upon multicarrier can be synthesized with suppressed mirror harmonic frequencies. It is shown that the proposed TMA DM transmitters here enjoy feeding network efficiency of 100%, and the transmit DM symbols can be synthesized at a pre-selected frequency only, significantly enhancing security performance. The effectiveness of the proposed scheme is validated via bit error rate (BER) simulations. Meanwhile, The TMA DM can also be used as a potential technique for the integrated sensing and communication (ISAC).