Research On Radio Frequency Stealth Technology In Airborne Radar Networks

With the developments of networks and information technology,networked combat systems will be the basic form of the warfare in the future.The developing direction of the warfare in the future is from “sensor-centric warfare” to “network-centric warfare”.Single radar or the simple combination of multiple radars cannot meet the needs of joint operation.Airborne radar network can provide real-time and transparent space perception for commanders through information fusion,which is based on the networked sensor system and is the developing direction of the radar in the future.However,hostile passive intercept system threatens the survivability and penetration ability of the airborne radar network in the battlefield.Under this background,this dissertation mainly discuss how to adaptively design the working parameters of the radar transmitter according to the target information,in order to achieve better radio frequency(RF)stealth performance for airborne radar network under the constraints of target detection and tracking performance.With the fully understanding of relevant research both at home and abroad,this thesis conducts an in-depth research on the transmit power allocation,resource management,and waveform design and optimization.In addition,the problem of transmitter subset selection in airborne radar network based on illuminators of opportunity is explored.In summary,the main contents of this thesis are listed as follows:1.The RF stealth based power allocation algorithm for target tracking in airborne radar network system is investigated.Firstly,due to the lack of analytical closed-form expressions for probability of detection and probability of false alarm,three information-theoretic criteria,namely,Bhattacharyya distance,Kullback-Leibler(KL)divergence,and J divergence are calculated and employed as the metrics for target detection performance in tracking process.Then,the problem of RF stealth based power allocation for target tracking in airborne radar network is formulated.The objective is to minimize the maximum transmit power of the radar by optimizing the power allocation among netted radars in the network to guarantee a predefined target tracking performance,which is based on the target motion.Finally,the nonlinear programming genetic algorithm(NPGA)is utilized to solve the resulting nonconvex,nonlinear,and constrained optimization problem.Numerical simulations demonstrate the superior RF stealth performance of the proposed algorithm over traditional monostatic phased array radar and unoptimized radar network system.2.The RF stealth based resource management algorithm for target tracking in airborne radar network system is investigated,where the radar network is composed of one dedicated radar transmitter and multiple receivers.Firstly,the intercept probability of radar network is derived and exploited as the optimization criterion for the RF stealth algorithm.Based on which,the problem of RF stealth based resource management for target tracking in airborne radar network is formulated.The resulting RF stealth optimization problem is to minimize the intercept probability by optimizing the revisit interval,dwell time,and transmitted power for a predetermined target tracking accuracy.Numerical simulations demonstrate that the RF stealth performance of the proposed algorithm outperforms existing algorithms.3.The problem of RF stealth based radar waveform design in airborne radar network system is investigated.Firstly,the extended target signal model for radar network is provided.Then,a signal-to-interference-plus-noise ratio(SINR)based radar waveform design algorithm is proposed to minimize the total transmit energy with a given SINR threshold for target detection performance,and a mutual information(MI)based radar waveform design algorithm is proposed to minimize the total transmit energy with a given MI threshold for target characterization performance.The Karush-Kuhn-Tucker(KKT)conditions are derived to solve the resulting problems.Recognizing that the precise knowledge of target spectra is impossible to capture in practice,it is assumed that the target spectra lie in uncertainty sets bounded by known upper and lower bounds.Based on this band model,the robust radar waveform design approaches for airborne radar network are developed based on SINR and MI criteria,respectively.Numerical simulations demonstrate that the proposed algorithms can efficiently improve the RF stealth performance for radar network system.It is also shown that the robust waveforms bound the worst-case RF stealth performance of the radar network at an acceptable limit.4.The problem of RF stealth based orthogonal frequency division multiplexing(OFDM)radar waveform design for spectrum sharing is investigated.Given the knowledge of the communication signals,the target spectra,and the propagation losses of corresponding channels,three different RF stealth based criteria for optimal radar waveform design are proposed to minimize the total transmit power of the radar system by optimizing the multicarrier radar waveform with a predefined MI constraint and a minimum required capacity for the communication system.These criteria differ in the way the scattering off the target due to the communication signals is considered as useful energy,as interference or ignored altogether at the radar receiver.The resulting problems are convex and solved analytically,where the KKT conditions are derived to solve these problems.However,the precise characteristics of target spectra are impossible to capture in practice,it is assumed that the target spectra lie in uncertainty sets bounded by known upper and lower bounds.Based on this model,the robust counterparts of the problems are proposed.Numerical simulations demonstrate that the RF stealth performance can be efficiently improved by exploiting the communication signals scattered off the target at the radar receiver.In addition,it is also shown that the robust waveforms bound the worst-case RF stealth performance of the radar at an acceptable limit.5.The problem of transmitter subset selection in airborne passive radar network based on frequency modulation(FM)is investigated.Firstly,the operating principle and feasibility of the FM based airborne passive radar network are analyzed,and the system model is formulated.Then,the Cramér–Rao lower bounds(CRLBs)on the Cartesian coordinates of Rician target position and velocity are computed.Simulation results are provided to show that the joint CRLB is not only a function of the relative geometry between the target and the radar network system but also a function of the transmitted waveform parameters.Finally,two transmitter subset selection schemes are proposed for FM based passive radar network.In the first,the subset size of selected transmitters employed in the estimation process is minimized by effectively selecting a subset of transmitters,such that the required target parameter estimation mean-square error(MSE)threshold is attained.In the second,an optimal subset of transmitters of a predefined size is selected,such that the estimation MSE is minimized.Both transmitter subset selection schemes are tackled with heuristic greedy selection algorithms.Numerical simulations demonstrate that better target parameter estimation accuracy can be obtained by utilizing only a fraction of transmitters of opportunity.Furthermore,it is shown that the proposed algorithms lead to reductions in both signal processing costs and computational load.