Research On Waveform Design And Parameter Estimation For LPI Radar

With the development of anti-radar technology, radar needs to improve its hidden performance, which makes itself not to be intercepted or difficult to be intercepted by the enemy, thus reducing the probability of being reconnaissance and jamming. With the performance of a certain low probability of intercept(LPI) has become the inevitable trend of radar against various electronic reconnaissance and interference measures.Aiming at the new development of the detection of low intercept signal, parameter estimation and beam scanning technology in the modern electronic battlefield,in this dissertation, and considering the optimal design of the transmission signal pattern and the inherent advantages of modern new system radar technology such as wideband radar technology, MIMO radar technology and frequency diversity array(FDA) radar technology, many methods on waveform optimization and parameter estimation for LPI radar are proposed. The main works and contributions of this dissertation are as following:(1) Waveform design with LPI performance for wideband MIMO radarCombined with the low interception characteristics of wideband signal and the waveform diversity of MIMO radar which is easy and flexible to design of transmission signal pattern, wideband MIMO radar becomes one of the important directions in the study of LPI performance radar. In this thesis, based on wideband MIMO radar signals, two approaches are proposed to synthesize the power spectral density matrix(PSDM) to approximate given beampatterns. The whole wide band signal is divided into a plurality of narrow band, and for each narrow band, the optimization problem with the desired sidelobe level and total transmit power constraint is established, thus power density matrix of the transmit signal vector is designed to make the pattern mainlobe to approximate a desired mainlobe response. The both proposed approaches are converted to the second-order cone programming(SOCP) problems by introducing new variables, and the minimum points of the new cost functions are solved by the convex optimization toolbox. Numerical simulation results show that the proposed approaches are effectiveness compared with the existing wideband beampattern design approach, as well as the designed beampatterns maintain a constant beamwidth across the entire frequency band. The effectiveness is verified by the numerical simulation results.(2) LPI performance and application research for frequency diversity array(FDA)As a novel array antenna model, FDA can realize the beam scanning in the space without phase shifter by introducing a small frequency increment between the array elements. It can provide a distance, angle and time dependent beampattern, and also it has unique advantages for radar to achieve its LPI performance. Focus on radar and electronic warfare, in this thesis, FDA and its frequency scanning characteristics is discussed. In essence shows some characteristics of a frequency diversity array as a time modulated array to decrease sidelobe levels and create multiple beams. The mathematical basis of FDA is established, and it shows that interelement frequency increment generates a range, time and angle-dependent pattern. At last, this thesis researches the applications of FDA and explores its potential LPI capabilities.(3) Joint range and angle estimation based on sub-array scheme for FDA RadarThe two-dimensional parameter localization of non-cooperative targets can not be obtained by the traditional linear phased array radar beam peak, and also it can’t estimate directly both the range and angle information of a target by uniform linear array FDA radar because of the coupling in range and angle responses. A sub-array scheme of range-angle joint estimation of a target for FDA radar is proposed in this thesis. The entire array is divided into two sub-arrays, which employs two different frequency offsets. For aperture extension, each sub-array adopts difference co-array structure to provide 2O(N) degrees of freedom by only N physical sensors when the second-order statistics of the received data is used. Therefore, the targets range and angle can be estimated directly with the subspace-based multiple signal classification algorithms. The estimation performance is examined by analyzing the Cramer-Rao lower bound(CRLB) versus signal-to-noise ratio(SNR). The effectiveness is verified by the numerical simulation results.(4) Beam optimization design of cognitive FDA-MIMO radar with LPI performanceThe essence of radar signal with LPI performance is expect to find targets in complex electromagnetic environments, at the same time, it is expected that emission signals not to be detected by the enemy as far as possible. In this thesis, we proposed a cognitive radar based on the FDA-MIMO radar to realize LPI performance, a scheme for waveform design with LPI performance is proposed, which is to minimize the energy in which the target is located and maximize the energy of the receiver. This is based on the range dependent characteristics of the frequency diversity array transmit beampattern. Then, the proposed energy distribution problem is conberted into a second-order non convex optimization problem(SONCP). By, the SONCP is solved by introducing a new variable. Two methods for solving the optimal solution are given in this thesis. Simulation results show that the proposed approach is effective.