Yiqing Liu

A two-element direction-finding method based on time modulated array (TMA) without sampling synchronization which exploits new asymmetric time sequences is proposed. The necessity of synchronization between the radio frequency (RF) switches and analog-to-digital converter (ADC) for existing direction-finding methods based on TMA and the influences of synchronization errors on the phases of different harmonics are firstly analyzed and modeled. By considering asymmetric time sequences and the mathematical relationship between adjacent harmonics, the proposed method can estimate the direction of arrival (DOA) without synchronization. Compared to the existing methods, the proposed method avoids the synchronization between the ADC and RF switches while keeps the similar accuracy performance. Numerical simulations are provided to show the feasibility and effectiveness of the proposed method. A simple Sband two-element TMA is fabricated to show the synchronization problem and verify the direction-finding method.

A novel beam scanning method utilizing the carrier frequency component for time modulated array (TMA) is proposed and a significant algorithm based on the non-uniform period modulation is implemented to suppress the maximum sideband radiation (SR) level. The signal in each channel is modulated by a pair of high-speed radio- frequency (RF) switches and totally three or four delay lines with different phases. In each modulation period, three selected delay lines are connected successively with proper pulse durations to keep the switches in ”ON” states constantly and ensure the maximum efficiency in the feeding network. Additionally, in order to suppress the relatively higher SR generated by both switches and delay lines, each channel of the TMA system has a different modulation period, which will separate the harmonic components of different elements on the frequency axis. A desired relatively low maximum SR level without complicated optimization is obtained compared to uniform period modulation and optimization algorithms. Several numeric simulations are brought out to examine the performance of the proposed methods, and the results for comparison to existing methods are also provided. A group of experiments have been done to verify its effectiveness.

A novel multi-user communication system based on the time modulated circular array (TMCA) has been proposed in this paper. Different modes of electromagnetic vortex waves are generated through TMCA by the transmitter and each mode carries different user's signal. To realize this mode-division multiplexing method, users' messages are modulated to different intermediate frequencies beforehand. Users' signals are received also by TMCA. Because of the modulation of the TMCA, different user's signal is moved to different frequencies so they can be distinguished by bandpass filters. The proposed method implements the mode-division multiplexing with a single RF channel, which has advantages in the hardware complexity and cost. The process of transmitting and receiving is analyzed, and the drawbacks are discussed. Simulations are conducted to verify its effectiveness.