Haihua Xie

Since its inception, the frequency diverse array (FDA) has attracted extensive attention and research because of its unique properties. However, most of the research primarily focuses on linear geometry FDA, with fewer studies on planar FDA. This letter proposes a design method based on planar rectangular FDA (PRFDA), which adjusts the frequency of each array element nonlinearly so that the beam direction of planar rectangular FDA can change linearly or nonlinearly with time, forming the desired transmit beampattern. Theoretical analysis and simulation results verify the effectiveness of the proposed method.

Due to the time‐varying phase in frequency diverse arrays (FDAs), traditional phase‐based secure communication (SC) methods cannot be utilized. In this reported work, the automatic scanning property of FDAs (time‐varying property) was rederived. This property allows for the presetting of the beam scanning time towards the desired receiver (Bob). Subsequently, this time‐carrying beam design was applied to Low Earth Orbit (LEO) satellites. A satellite‐to‐ground communication method is proposed based on time intervals, which effectively prevents the interception of information by an undesired receiver (Eve). Simulation results are presented to validate the effectiveness of the proposed method.

Unlike phased array, frequency diverse array (FDA) applies a tiny frequency offset across the antenna elements to generate a range-angle-dependent beampattern. However, due to the range-angle coupling property, the emitter position cannot be obtained directly from conventional FDA beamforming peaks. This paper proposes a novel passive localization approach based on direction modulation (DM) and Chan algorithm. By applying DM, the angle-range coupling can be wiped off well, which has a significant influence on the emitter localization. Simulation results are implemented to verify the validity and superiority of the proposed technique.

The conventional frequency diversity array (FDA) can generate arcsine form of continuous direction modulation (DM) waveforms which can automatically scan the entire space range. However, the single waveform and time varying phase of FDA cannot meet the requirements of practical security communication application scenarios. Thus, a new transmit diversity technique, called time frequency direction modulation (TFDM), is proposed to improve azimuth security. In this paper, unique time-frequency information at a given azimuth was formed by designing the beam steering term and the frequency term of each array element on the basis of the time varying characteristics of the FDA. In a transmit duration, DM can be divided into linear DM (LDM) and nonlinear DM (NDM) according to the beam shape. For LDM, for a specific observation direction, the frequency reaches the set value when the beam energy reaches the maximum value when the beam scans to this direction, but the uniqueness of time frequency information no longer exists in other directions. For NDM, the beam can pass through a given azimuth multiple times and form multiple pairs of time-frequency information, which provides a new idea for realizing multi-directional communication and solving communication rate problems. Finally, the uni-directional and multi-directional communication based on three different safe communication methods: time-direction modulation (TDM), frequency-direction modulation (FDM), and time-frequency-direction modulation (TFDM) are realized and the validity of the proposed method and the corresponding theory are verified by extensive numerical results.