Research On Signal Processing Of Heterogeneous Sky-Wave Radar

Sky-wave over-the-horizon radar(OTHR)radiates electromagnetic waves to the atmospheric ionosphere,and then refracts the electromagnetic waves to reach farther ground and sea areas.Since it uses high-altitude ionospheric emission detection methods,OTH radar can detect targets that are blocked by the curved surface of the earth and the detection range has reached 800-3500 kilometers.OTH radar plays an important strategic role in the fields of surveillance,air defense and early warning.In the research on OTH radar,problems such as how to rationally arrange large-scale arrays under geographically restricted conditions to achieve beamforming and how to effectively detect slow and weak targets in a strong clutter background have always affected the efficient application of sky-wave radar.Array optimization arrangement and adaptive detection,as very important technical means in signal processing,can be used to solve some of the above problems.The main contributions and innovations of this dissertation can be summarized as follows:1.The traditional uniform rectangular two-dimensional OTH array occupies a large area and is easily limited by geographical factors.Aiming at this problem,an optimization algorithm for heterogeneous OTH array based on 0/1 constraints is proposed considering geographical constraints.By converting geographic constraints into 0/1 constraints,the OTH array is guaranteed to complete the sparse array optimization arrangement under the condition of satisfying the terrain constraints,and finally obtains the pattern that meets the performance requirements of the OTH radar.2.The function of the traditional two-dimensional OTH array is relatively single,and it cannot form multiple beams at the same time to achieve multiple functions.To solve this problem,two simultaneous multi-beam heterogeneous array optimization algorithms based on array element selection are proposed,and the "sub-array division" is completed in a step-by-step and synchronous manner,so that the OTH array can simultaneously form multiple beams in different directions and it is versatile.3.In practical applications,it may be necessary to synthesize a large-scale array from several sub-arrays of different shapes.Aiming at this problem,a joint optimization algorithm of heterogeneous array position and placement angle based on sub-array selection is proposed.Through the flexible placement of small-scale heterogeneous subarrays,the sub-arrays do not overlap each other and the finally optimized heterogeneous OTH array has the function of " electric scanning".4.Aiming at the problem of OTH radar detecting slow targets in the sea,it is modeled as a compound Gaussian distribution with gamma texture by fitting the amplitude distribution of sea clutter,and the MAPGLRT-PFP detector is derived according to the generalized likelihood ratio test(GLRT)criterion under the two-step maximum a posteriori(MAP).The AR-GLRTS detector is derived under the GLRT criterion by approximately fitting the autoregressive(AR)model to the sea clutter power spectrum.Compared with traditional detectors,the detection performance of the proposed detector is greatly improved under the condition of small samples,which makes it easier for radar to detect slow targets in the undulating sea clutter background.