Directional Modulation in Time-Modulated Array With a Novel Pseudorandom Ascending Phase Time Sequence

Directional Modulation With Artificial-Noise Injection Into Time-Modulated Arrays

“…Spectral aliasing only happens when the signal bandwidth (B) exceeds the time modulation frequency (f 0 ). This lack of frequency orthogonality allows for the transmission of direction-dependent signals in time-varying scenarios provided that the instrumental parameters of the TMA modulating periodic sequences (i.e., the time delay and/or the duration time in on-state) are optimized [1]- [3]. Therefore, in the existing TMA techniques, time-sensitive optimization algorithms are indispensable to ensure a two-fold objective: (1) to guarantee spatial orthogonality in the desired direction between the exploited harmonic pattern and those of the remaining harmonics, thus ensuring null or negligible sideband signal levels in the desired direction; and (2) to sufficiently distort (thanks to spectral aliasing) the information signal (IS) in all other directions but the desired one.…”

“…This lack of frequency orthogonality allows for the transmission of direction-dependent signals in time-varying scenarios provided that the instrumental parameters of the TMA modulating periodic sequences (i.e., the time delay and/or the duration time in on-state) are optimized [1]- [3]. Therefore, in the existing TMA techniques, time-sensitive optimization algorithms are indispensable to ensure a two-fold objective: (1) to guarantee spatial orthogonality in the desired direction between the exploited harmonic pattern and those of the remaining harmonics, thus ensuring null or negligible sideband signal levels in the desired direction; and (2) to sufficiently distort (thanks to spectral aliasing) the information signal (IS) in all other directions but the desired one. Optimization is necessary for multi-carrier TMAdirectional modulation (DM) and direct antenna phase-shift keying (PSK) modulation [4], [5], whereas advanced optimization algorithms are required in non-TMA-DM techniques based on the injection of artificial noise (AN) into all spatial directions except the IS transmission direction [6], [7].…”

Programming nonreciprocity and harmonic beam steering via a digitally space-time-coded metamaterial antenna

“…On the other hand, time modulation has also been applied to antenna arrays [28], in which a predetermined periodic sequence can achieve side lobe reduction for the fundamental frequency pattern [29]. Moreover, generated harmonic components can be leveraged to provide physical layer security in wireless communication as well as enable radar detection [30][31][32][33][34][35][36][37][38][39][40][41][42]. Nevertheless, for conventional time modulated antenna arrays, pin diodes are usually employed as RF switches that decrease the power efficiency due to power dissipation in their off state [43].…”