Waveform Design And High-resolution Range Profile Synthesis For Random Hopping Frequency Radars

In the process of missile terminal guidance,active radar guidance has gradually become the mainstream guidance mode of future missile weapon system.In the increasingly complex electromagnetic environment of the future battlefield,it is very necessary to effectively enhance the low interception and anti-jamming performance of active radar seeker signal for improving the survival and attack capability of missile.In view of this,this paper focuses on the key issues of the waveform design and high-resolution range profile(HRRP)synthesis of random frequency hopping(RFH)radar.The researches include the design of the low-sidelobe frequency pattern of transmitted waveform,the synthesis of HRRP,the Doppler sensitivity of range profile and the motion compensation.The main work and achievements are summarized as follows:Firstly,the signal model of the transmitted pulse-train waveform of RFH radar is constructed.The integral expression of range-velocity two-dimensional ambiguity function is deduced.The high resolution performance of radar waveform in range-velocity dimension is analyzed.Then,the baseband sampling echo signal of an ideal point target is introduced to provide the theoretical basis for subsequent analyses.The RFH radar has a thumbtack-type ambiguity function,which is capable of effectively overcoming the problem of range ambiguity and efficiently improving the ability to antagonize the inter-pulse repeater active interference.Secondly,aiming at the issue of the waveform design of RFH radar,a modulation frequency design method based on equal-area segmentation window function is proposed in this paper,to obtain the transmitting frequency hopping pattern with ultra-low range sidelobes.The range ambiguity function with ultra-low sidelobes is helpful to improve radar detection performance of weak target in the strong clutter environment.The randomness of modulation frequencies provide good flexibility for waveform design.The spectrum of transmitted signal is controlled by the distribution of modulation frequencies.When the distribution density shapes as a window function,the sidelobes of range ambiguity function can be effectively suppressed.The method is simple and easy to implement.In addition,the non-uniformity characteristics of modulation frequencies also weaken the gate-lobe constraint condition between radar pulse width and frequency hopping interval,and facilitate the optimal design of waveform parameters in radar system applications.Thirdly,aiming at the issue of radar HRRP synthesis during the coherent guidance process,the kernel function correlation method and the zero-padding IDFT method with low computational complexity are proposed in this paper.The HRRP could realize pulse compression of radar echoes,improve ranging accuracy,obtain more detailed information of the target,and also help to improve the output signal-to-noise ratio.Compared with the traditional matched filter method,the proposed methods possess lower sampling rate and computational complexity,but could bring about the same signal-to-noise ratio improvement.Therefore,the RFH radar adopting the proposed methods to synthesize the HRRP can be implemented in narrowband and reduce the cost.At last,the effectiveness of the proposed methods is verified by the simulated and out-field measured experiments.Finally,aiming at the defocusing problem of RFH adar during the process of HRRP synthesis of the moving targets,this paper presents an accurate velocity estimation method based on the cross-correlation of the adjacent range profiles and minimum waveform entropy,and based on the complementary code modulation to achieve the phase compensation for sampling echoes.The echo phases of moving target are disturbed by the radial velocity,which may result in that the HRRP energy of target can not be concentrated and entirely scattered in the random sidelobes.At first,the paper derives the velocity tolerance that does not de-focus the HRRP of moving target seriously.Then,the above two methods,which is capable of effectively satisfying the requirements of motion compensation accuracy,are introduced.The former method combines the advantages of the coarse velocity measurement by HRRP cross-correlation and high accuracy of waveform entropy.It has the characteristics of fast convergence and wide range of velocity measurement.While,the latter method achieves the separation of target range and velocity in the echo phases via designing the complementary modulation frequencies of adjacent transmitted waveforms.Thus,the target velocity can be coherently accumulated and measured.The method is characterized by high velocity measurement accuracy,low computational complexity and improved signal-to-noise ratio.