Research On Directional Modulation Technology Of Frequency Diverse Array

Conventional phased arrays achieve beam steering by introducing linear phase progression between adjacent elements.Frequency diverse array(FDA)introduces an additional tiny frequency shift across the array elements resulting in a range-angle dependent and time-variant beampatterns.Therefore,the beam scanning ability of FDA is more flexible.Directional modulation utilizes the spatial modulation capability of multi-antenna transmitting array to synthesize the digital modulation signal with directional characteristics at the transmitter,which ensures the secure transmission of the desired direction signal,and at the same time distorts the signal in the unexpected direction.This thesis focuses on the research of directional modulation technology of frequency diverse array.The main work is summarized as follows:A wireless communication scheme based on frequency diverse array is proposed.The normal working state of the frequency diverse array is determined by constructing a uniform circular frequency diverse array at the transmitting terminal and performing time modulation and nonlinear processing on the frequency offset of the antenna element.Furthermore,the phases of the antenna elements are optimized by using an enhanced particle swarm algorithm(EPSO).On this basis,the quadrature phase shift keying signals are transmitted,and the legitimate user receives the signal by using the corresponding receiver to calculated the bit error rate.Considering that the performance of the array antenna is degraded due to various errors in the frequency diversity array antenna system,a mathematical model of channel errors is established of the FDA with amplitude errors,phase errors and frequency offset errors.The pattern of the frequency diverse array error model is deduced.The radiation characteristics of the pattern in the presence of channel errors in FDAs are analyzed theoretically.Finally,the simulation results verify the theoretical analysis results of the frequency diversity array radiation pattern when there exist amplitude errors,phase errors and frequency offset errors.The effect of channel errors of frequency diverse array on the performance of the directional modulation communication system is studied.Starting with a one-dimensional logarithmic FDA as the transmitter,the phases of the array elements are optimized.At the receiving terminal,the legal receiver performs demodulation to obtain a distortion-free transmission signal to realize secure transmission of the target area information.Furthermore,considering the non-idealities in engineering applications,the channel error of the FDA is introduced into the directional modulation direction system.Theoretically,the performance change of the communication system with channel errors is deduced and the theoretical analysis results are verified by numerical simulations.