Waveform Designing Techniques On MIMO Radar For Clutter Rejection

Range ambiguity or range-clutter-folding,and Doppler ambiguity or Doppler-frequency-aliasing are important for radar in clutter rejection performance,which can not be available in publications on MIMO radar using orthogonal waveforms as detecting signal.Basing on the definition of the unambiguous region firstly introducedin the desertion,two basic types of coherent MIMO radar and non-coherent MIMO radarboth using orthogonal frequency waveforms are researched on the ambiguity properties,including the gridlobe and sidelobe level,the unambiguity delay,the unambiguity Doppler,and the unambiguity area in delay-Doppler plane.The phenomenon of reduction of the unambiguous area is discovered,and the waveform optimizing techniques are proposed to expand the unambiguity area to be 4(dimensionless).And a novel signal model of High Dimension of Frequency Separated Waveform Set(HDFSWS)isconstructed,the ambiguity properties of HDFSWS are derived,and the HDFSWS designing techniquesfor any size of unambiguity region areadvanced.The study is oriented from a theoretical research on the ambiguity function and waveform designing techniques,and is ended on a new approach for improving the MIMO radar on detecting targets performance in clutters,especially in the short-range clutters,and a closed loop from the theoretical research to the engineering techniques are obtained in the desertion.During the research three original results are achieved as follows:First,the reduction phenomenon of the MIMO unambiguous area is derived and obtained in the dissertation,and the waveform designing techniques for unambiguous area expansion are put forward.For the two types of coherent and noncoherent MIMO radar using N orthogonal waveforms each has the same baseband signal,the unambiguous area is proved in mathematical form to be 4/N and the less.The reduction of the unambiguous area will deteriorate the range-clutter-folding and Doppler-frequencyaliasing,and will lead the performance of detecting in cluttersto decline.And a novel waveform designing techniques to expand the unambiguous area to be 4 is proposed,through which the MIMO radar can match the SIMO radar on the range-folding and Doppler-frequency aliasing properties.Second:a novel waveform set optimization techinuqes for ambiguity gridlobe and sidelobe rejection is proposed,which can control the range clutters and Doppler clutters.For coherent MIMO radar,the delay gridelobes are cut off about20 dB,and the sidelobes are also cut down.And the Doppler sidelobes of coherent MIMO radar in the Doppler area |fd|?1/T are cut down to be near the level of that of the SIMO radar.Third,a novel waveform set model named HDFSWS modulated in space-time-frequency dimensions is constructed for MIMO radar,and the waveform designing techniques on HDFSWS are advanced.The novel waveform set HDFSWS can keep the frequencyorthogonality between any two waveforms inthe set,and can introducefrequencycodes on subpulses in each waveform.So HDFSWS is a type of frequency coding waveform in space-time-frequency dimensions.The ambiguity function of HDFSWS isderived in the desertion,and the sufficient condition on which the unambiguous size of the MIMO radar using HDFSWS equals the size of SIMO radar is deduced theoretically.Furthermore,the HDFSWSdesigning techniques forany size of the unambiguous region are brought forward.Four,a novel type of radar named Unambiguous MIMO Radar is put forward for shedding light on solving the problem of short-range clutter shielding on the targets.Basing on the HDFSWS with sufficient large size of the unambiguous region,the Unambiguous MIMO Radar can detect targets without ambiguity in range and Doppler,thus the range clutter should not be folded to alias with targets.The Unambiguous MIMO Radar promises appliance in AWACS,fighter plane,UAV and airship radars working in clutters.