Research On Multipath Effect Suppression And Key Technologies In Low-Angle Measurement Of Meter Wave Radar

The meter wave radar has attracted much attention due to its anti-stealth performance and its superior performance against anti-radiation missiles.Due to the long wavelength of the meter wave band,the size of the meter wave radar antenna is limited.Hence,the bandwidth of the meter wave radar antenna in pitching dimension is wide.When the low elevation angle target is detected,the direct wave and reflected wave are usually within a beam width.It is difficult for the meter wave radar to distinguish the direct wave from the ground reflected wave in the spatial,time and frequency domains.The multipath effect seriously affects the performance of the meter wave radar in the low elevation area.The poor accuracy of low angle estimation for meter wave radar is still a challenge problem.Therefore,based on the meter wave radar,this paper studies the strategy of suppressing the multipath effect of the ground environment and the methods of improving the accuracy of the angle measurement in the low elevation angle of the meter wave radar.The main contents are summarized as follows:1.The mechanism of the influence of the half-space environment on the radiation of the meter wave antenna is studied.Then the strategy of suppressing the influence of the multipath effect is studied and analyzed from the antenna half-space radiation model.The far field of the meter wave antenna in the low elevation angle region in the half-space is mainly composed of two parts: the direct wave component and the reflected wave component.And the ground reflected wave component is the main reason for the splitting of the wave antenna of the meter wave antenna,upturned,and covering discontinuities.The influence of multipath on the ground can be eliminated by increasing the antenna aperture in pitching dimension,but it is difficult to achieve in the meter wave band due to the limitation of antenna size.The height diversity,frequency diversity and paving the ground can suppress ground multipath effect to some extent,but it cannot fundamentally eliminate the multipath effect.2.The low elevation angle measurement model of the meter wave radar is studied,and the Cramér–Rao Bound of the low elevation angle estimation under the multipath model with different prior information is derived.The priori information of the multipath model also affects the angular accuracy of the low elevation algorithm.We derive the Cramér–Rao Bound(CRB)of the low elevation angle under the different priori information multipath models.The simulation results show that the more prior information of the multipath model,the lower the CRB value,that is,the higher the angular accuracy of the corresponding low elevation angle measurement algorithm.In addition,under the same physical caliber,since MIMO radar utilizes spatial diversity,it has a lower CRB with lower elevation angle estimation than phased array radar.3.The enhanced polarization smoothing low elevation estimation algorithms are studied.Since the difference between the vertical polarization and the horizontal polarization reflection coefficient is small in the low-angle region,the decoherence performance of the polarization smoothing algorithm is poor,resulting in poor accuracy of low-angle estimation.We implement the quadratic technique into the polarization smoothing algorithm,and propose a Quadratic Polarization Smoothing algorithm(Q-PS),and a Quadratic Polarization Smoothing Forward/Backward Space Smoothing algorithm(Q-PS-FB).In comparison with the polarization smoothing algorithm,Q-PS and Q-PS-FB algorithm can effectively improve the condition number of the polarization smoothing algorithm in the low elevation angle region,which can improve the low-angle estimation performance.In addition,since the Q-PS-FB algorithm utilizes both polarization smoothing and spatial smoothing,its de-coherent performance is better in low elevation angle regions.Therefore,the proposed algorithm improves the angular measurement performance of low elevation angle regions to some extent.4.The generalized MUSIC algorithm based on the dual polarization array is studied.In order to solve the problem of poor performance of the single-polarization generalized MUSIC algorithm when the phase of multipath attenuation coefficient is ?180?,the generalized MUSIC algorithm based on the dual polarization phased array and MIMO radar is proposed,respectively.Unlike the polarization smoothing algorithm,its low elevation angle measurement performance depends on the decoherence performance in the low-angle region.The PS-GMUSIC algorithm uses a composite steering vector,so it does not need to perform decoherence operation,and also because of the difference between the vertical polarization and horizontal polarization multipath attenuation coefficient,the PS-GMUSIC algorithm can effectively improve the low-angle estimation performance of the single-polarized generalized MUSIC algorithm when the the phase of the multipath attenuation coefficient is ?180?.5.According to the half-space radiation theory of the meter wave antenna,the phase stationary conception is proposed.It can prove that the reciprocity condition of applying TR technology in the low elevation environment is approximately established.Then an adaptive time-reversed focusing technique is proposed.Although the phase of the far field over the half-space varies greatly,its multipath response function remains relatively stable.Therefore,we propose the concept of the far field phase stationary zone based on the multipath response function.The phase change of the multipath channel response function does not exceed 2 degrees in the phase stationary zone,so the reciprocity condition holds for the TR technique.Based on the concept of phase stationary zone,we propose Adaptive Time Reversal(ATR),which adaptively adjusts the antenna feed phase according to the target elevation angle over half-space,to focus in the target direction and eliminate the influence of the multipath component.6.The low-angle measurement algorithm based on adaptive time reversal focusing is studied.Based on the concept of the phase stationary zone in the low-angle area,an adaptive time reversal MUSIC(ATR MUSIC)low elevation angle measurement algorithm is proposed based on phased array and MIMO radar,respectively.The ATR MUSIC algorithm matches the multipath response function through an adaptive time reversal matrix,which doesn't need the decoherence processing.And the Beam Space(BS)technique is used to reduce the computational complexity of the proposed algorithm.At the same time,the angular resolution of the proposed algorithm can be improved.Unlike the ATR MUSIC algorithm which based on the phased array,the ATR MUSIC algorithm based on MIMO radar requires the adaptive time-reversed matching matrix to simultaneously match the transceiving multipath channel response function.Moreover,the effect of mismatching problem for ATR strategy can be eliminated by the constraints.Since the ATR strategy can eliminate the influence of the multipath component totally,the ATR MUSIC algorithm has much superior low elevation angle measurement performance.