CN117805854B - Laser SAL wide-field imaging device and method based on MIMO - Google Patents
Laser SAL wide-field imaging device and method based on MIMO Download PDFInfo
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Abstract
本发明提供一种基于MIMO的激光SAL宽视场成像装置及方法,属于合成孔径激光雷达宽视场成像领域,借鉴微波多输入多输出合成孔径雷达SAR技术,解决激光宽视场和远距离探测问题,提出多输入多输出阵列合成孔径激光雷达,构建光学微透镜阵列,实现方位向和距离向大视场,在此基础上,通过阵列发射实现视场内的光场能量叠加,利用不同收、发通道组合形成不同位置等效相位中心信号,实现高分辨率宽测绘带合成孔径激光雷达成像。本发明采用MIMO的阵列合成孔径激光雷达技术,多个通道同时发射和接收相互可分离的发射波形,完成合成孔径激光雷达成像。
The present invention provides a MIMO-based laser SAL wide-field imaging device and method, which belongs to the field of synthetic aperture laser radar wide-field imaging, draws on microwave multi-input multi-output synthetic aperture radar SAR technology, solves the laser wide field of view and long-distance detection problems, proposes a multi-input multi-output array synthetic aperture laser radar, constructs an optical microlens array, and realizes a large field of view in azimuth and distance. On this basis, the light field energy superposition in the field of view is realized through array transmission, and different receiving and transmitting channel combinations are used to form equivalent phase center signals at different positions, so as to realize high-resolution wide-surveying-band synthetic aperture laser radar imaging. The present invention adopts MIMO array synthetic aperture laser radar technology, and multiple channels simultaneously transmit and receive mutually separable transmission waveforms to complete synthetic aperture laser radar imaging.
Description
技术领域Technical Field
本发明属于合成孔径激光雷达(Synthetic Aperture Ladar, SAL)宽视场成像领域,具体涉及一种基于多输入多输出(Multiple-Input-Multiple-output,MIMO)的激光SAL宽视场成像装置及方法。The present invention belongs to the field of synthetic aperture laser radar (Synthetic Aperture Ladar, SAL) wide field of view imaging, and specifically relates to a laser SAL wide field of view imaging device and method based on multiple-input multiple-output (Multiple-Input-Multiple-output, MIMO).
背景技术Background technique
2000年以来,随着激光技术和合成孔径技术的成熟,国内外掀起对合成孔径激光雷达成像研究的热潮。目前对激光SAL的研究主要是单发单收SAL体制,作为远距离高分辨率观测的一种理想方式,激光SAL技术朝着更高分辨率、更远作用距离、更大测绘幅宽方向发展。Since 2000, with the maturity of laser technology and synthetic aperture technology, there has been a boom in synthetic aperture lidar imaging research at home and abroad. At present, the research on laser SAL is mainly based on the single-transmitter single-receiver SAL system. As an ideal way to observe long-distance high resolution, laser SAL technology is developing towards higher resolution, longer range, and larger mapping width.
在传统的单发单收SAL体制中,远距离探测时常用的激光发散角较小,且距离向测绘带宽和方位向分辨率之间的矛盾是无法避免的,限制了激光SAL技术的应用。造成距离向测绘带窄的原因主要有两个:In the traditional single-transmitter single-receiver SAL system, the laser divergence angle commonly used for long-distance detection is small, and the contradiction between the range mapping bandwidth and the azimuth resolution is inevitable, which limits the application of laser SAL technology. There are two main reasons for the narrow range mapping bandwidth:
第一、激光波长短,波束窄,激光SAL的距离向测绘带宽受到系统距离向波束宽度的影响,增大波束宽度会增加测绘带宽度,同时也会降低探测距离,即存在发散角与探测距离之间的矛盾,难以实现远距离宽测绘带;First, the laser wavelength is short and the beam is narrow. The distance mapping bandwidth of the laser SAL is affected by the distance beam width of the system. Increasing the beam width will increase the mapping swath width, but will also reduce the detection distance. That is, there is a contradiction between the divergence angle and the detection distance, making it difficult to achieve a long-distance wide mapping swath.
第二、距离向测绘带宽与方位向分辨率之间的矛盾,这种矛盾来源于它们对系统脉冲重复频率(pulse repeat frequency, PRF)的不同要求。单发单收激光SAL体制在方位向高分辨率观测时,其距离向测绘带宽会被限制到一定范围内。Second, there is a contradiction between the range mapping bandwidth and the azimuth resolution, which is caused by their different requirements for the system pulse repeat frequency (PRF). When the single-transmitter and single-receiver laser SAL system performs high-resolution observations in azimuth, its range mapping bandwidth will be limited to a certain range.
为了解决上述第一个问题,在发射接收天线中采用多发光纤阵列作为光源,增加距离向的阵元个数,如西安电子科技大学唐禹课题组采用距离向多发多收期望实现距离向宽测绘带。对于第二种原因,唐禹课题组采用方位向多发多收来增大方位向发散角,实现合成孔径激光雷达高方位分辨率成像,以上两种方案在理论上解决了方位向高分辨率和距离向幅宽的问题,但考虑常用光源的出光纤芯直径为10μm,包层直径为127μm,光纤阵列最小间隔为127μm,阵元间填充因子为10/127,填充因子定义为阵元直径与阵元间距的比值,对于上述距离向多发SAL,阵列光源在远场成像为多个分离的成像区域,难以实现测绘带的连续扩展。对于上述方位向多发多收合成孔径激光雷达,方位向阵列光源在远场成像为多个分离的成像区域,难以连续增加方位向波束宽度。In order to solve the first problem mentioned above, a multi-fiber array is used as the light source in the transmitting and receiving antenna to increase the number of array elements in the range direction. For example, Tang Yu's research group at Xidian University uses multi-transmit and multi-receive in the range direction to achieve a wide range mapping zone. For the second reason, Tang Yu's research group uses multi-transmit and multi-receive in azimuth to increase the divergence angle in azimuth and achieve high azimuth resolution imaging of synthetic aperture lidar. The above two solutions theoretically solve the problems of high resolution in azimuth and width in range. However, considering that the core diameter of the optical fiber of the commonly used light source is 10μm, the cladding diameter is 127μm, the minimum spacing of the optical fiber array is 127μm, and the filling factor between array elements is 10/127. The filling factor is defined as the ratio of the diameter of the array element to the spacing between the array elements. For the above multi-transmit SAL in the range direction, the array light source is imaged as multiple separated imaging areas in the far field, making it difficult to achieve continuous expansion of the mapping zone. For the above multi-transmit and multi-receive synthetic aperture lidar in azimuth, the azimuth array light source is imaged as multiple separated imaging areas in the far field, making it difficult to continuously increase the azimuth beam width.
发明内容Summary of the invention
针对以上问题,考虑现实中成像不连续的技术难题,本发明提供一种基于MIMO的激光SAL宽视场成像装置及方法,借鉴微波MIMO SAR技术,解决发散角和探测距离的矛盾,提出多发多收阵列激光SAL,构建光学小口径微透镜阵列,通过小口径实现宽视场,在宽视场的基础上,采用微透镜阵列增加视场内光场能量,提高探测距离,利用不同收、发通道组合形成不同位置等效相位中心信号,满足高分辨率宽测绘带的激光SAL成像应用需求。In view of the above problems and considering the technical difficulties of discontinuous imaging in reality, the present invention provides a MIMO-based laser SAL wide-field imaging device and method, draws on microwave MIMO SAR technology to solve the contradiction between divergence angle and detection distance, proposes a multi-transmitter and multi-receiver array laser SAL, constructs an optical small-aperture microlens array, and realizes a wide field of view through a small aperture. On the basis of the wide field of view, a microlens array is used to increase the light field energy in the field of view and improve the detection distance. Different combinations of transmit and receive channels are used to form equivalent phase center signals at different positions, thereby meeting the application requirements of laser SAL imaging with high resolution and wide mapping band.
为达到上述目的,本发明采用如下技术方案:In order to achieve the above object, the present invention adopts the following technical scheme:
一种基于MIMO的激光SAL宽视场成像装置,包括方位向4列、距离向4行的16个阵列收发装置,阵列收发装置间形成MIMO模式,阵列收发装置包括发射系统和接收系统;所述发射系统包含激光源、调制模块、光放大模块、发射光纤阵列和微透镜阵列;所述接收系统包括阵列探测单元和阵列采集成像处理单元;发射光纤阵列和微透镜阵列组成发射阵列,阵列探测单元构成接收阵列;每个发射光纤阵列用于发射激光束,发射的激光束通过微透镜阵列准直照射到远场,以获得更大的测绘带宽;回波信号进入阵列探测单元,然后进入阵列采集成像处理单元进行阵列采集成像处理。A MIMO-based laser SAL wide-field imaging device comprises 16 array transceiver devices with 4 columns in azimuth and 4 rows in distance, wherein a MIMO mode is formed between the array transceiver devices, and the array transceiver device comprises a transmitting system and a receiving system; the transmitting system comprises a laser source, a modulation module, an optical amplification module, a transmitting optical fiber array and a microlens array; the receiving system comprises an array detection unit and an array acquisition imaging processing unit; the transmitting optical fiber array and the microlens array constitute a transmitting array, and the array detection unit constitutes a receiving array; each transmitting optical fiber array is used for emitting a laser beam, and the emitted laser beam is collimated and irradiated to a far field through a microlens array to obtain a larger surveying and mapping bandwidth; an echo signal enters the array detection unit, and then enters the array acquisition imaging processing unit for array acquisition imaging processing.
本发明还提供一种基于MIMO的激光SAL宽视场成像方法,包括如下步骤:The present invention also provides a MIMO-based laser SAL wide-field imaging method, comprising the following steps:
步骤1) 根据激光SAL应用中分辨率和幅宽的要求,设计发射光束方位和距离向发散角;Step 1) Design the azimuth and range divergence angle of the emitted beam according to the resolution and width requirements in the laser SAL application;
步骤2)根据探测距离需求,基于雷达方程,确定方位向和距离向的多发多收阵列的个数,设计与发射光纤阵列对应的微透镜阵列,构成多发多收阵列;Step 2) According to the detection distance requirement and based on the radar equation, determine the number of multiple-transmit and multiple-receive arrays in azimuth and range directions, design a microlens array corresponding to the transmitting optical fiber array, and form a multiple-transmit and multiple-receive array;
步骤3)假设带有微透镜阵列的多发多收阵列为二维阵列,其中发射系统的每一个发射光纤和对应的微透镜为一个发射阵元,经过微透镜阵列合成得到近场光束振幅;Step 3) Assume that the multi-transmitter multi-receiver array with a microlens array is a two-dimensional array, in which each transmitting optical fiber and the corresponding microlens of the transmitting system are a transmitting array element, and the near-field beam amplitude is obtained by synthesizing the microlens array;
步骤4)将远场光强分布看作微透镜阵列的输出光场的傅里叶变换,从而获得多发多收阵列的出射光在远场形成的场分布;Step 4) The far-field light intensity distribution is regarded as the Fourier transform of the output light field of the microlens array, thereby obtaining the field distribution formed by the output light of the multi-transmitter and multi-receiver array in the far field;
步骤5)计算不同排布方式时,根据多发多收阵列的出射光在远场形成的场分布以及远场光斑能量分布,得到多发多收阵列的发射位置和接收位置的最佳排布方式。Step 5) When calculating different arrangements, the optimal arrangement of the transmitting position and receiving position of the multi-transmitter multi-receiver array is obtained according to the field distribution formed by the output light of the multi-transmitter multi-receiver array in the far field and the energy distribution of the far-field light spot.
有益效果:Beneficial effects:
(1)本发明利用方位和距离向阵列小口径分布方式,实现大成像视场。(1) The present invention utilizes the small aperture distribution of the azimuth and distance arrays to achieve a large imaging field of view.
(2)在小口径镜头基础上,利用阵列发射单元合束的方式,提高视场内能量分布,实现远距离宽幅探测。(2) Based on a small-aperture lens, the array transmitting unit is combined to improve the energy distribution in the field of view and achieve long-distance and wide-band detection.
(3)本发明利用多个阵列发射和接收相互可分离的波形,根据现有微透镜阵列的排布技术,模拟和设计阵列发射系统,产生具有高主瓣能量的成像发射和接收装置。(3) The present invention utilizes multiple arrays to transmit and receive separable waveforms, simulates and designs an array transmission system based on the existing microlens array arrangement technology, and generates an imaging transmission and receiving device with high main lobe energy.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1是本发明实施例的基于MIMO的激光SAL宽视场成像装置示意图;FIG1 is a schematic diagram of a MIMO-based laser SAL wide-field imaging device according to an embodiment of the present invention;
图2为发射光纤和对应微透镜排布示意图;FIG2 is a schematic diagram of the arrangement of the transmitting optical fiber and the corresponding microlenses;
图3为激光SAL二维4×4发射阵列及远场光斑分布图;Figure 3 is a 2D 4×4 laser SAL emission array and far-field spot distribution diagram;
图4a为等间距多发多收阵列远场光束分布图;FIG4a is a far-field beam distribution diagram of an equally spaced multiple-transmitter and multiple-receiver array;
图4b为等间距多发多收阵列远场光束的光强分布图;FIG4b is a diagram showing the intensity distribution of the far-field beam of an equally spaced multi-transmitter and multi-receiver array;
图5a为优化后的多发多收MIMO稀疏阵列远场光斑分布图;FIG5a is a far-field spot distribution diagram of the optimized multi-transmit multi-receive MIMO sparse array;
图5b为优化后的多发多收MIMO稀疏阵列远场光斑的光强分布图。FIG5b is a diagram showing the intensity distribution of the far-field spot of the optimized multi-transmit multi-receive MIMO sparse array.
具体实施方式Detailed ways
本发明采用二维阵列多发多收的方式实现激光SAL高分辨率宽视场成像,同时利用优化算法来设计多发多收的阵元排布,实现高的主瓣能量和低的旁瓣能量;各接收探测器同时接收回波数据,根据不同的发射波形,采取相应的波形分离方法(如发射同频正交波形时,利用匹配滤波方法),将不同发射波形的回波进行分离,得到不同收发组合的回波,然后将所有收发组合的回波进行相干成像处理。同时,本发明采用理论仿真模拟的方法进行验证,验证了本发明装置的有效性。The present invention uses a two-dimensional array multi-transmit and multi-receive method to achieve laser SAL high-resolution wide-field imaging, and uses an optimization algorithm to design the multi-transmit and multi-receive array element arrangement to achieve high main lobe energy and low side lobe energy; each receiving detector receives echo data at the same time, and adopts a corresponding waveform separation method according to different transmission waveforms (such as using a matched filtering method when transmitting orthogonal waveforms of the same frequency), separates the echoes of different transmission waveforms, obtains echoes of different transmission and reception combinations, and then performs coherent imaging processing on the echoes of all transmission and reception combinations. At the same time, the present invention uses a theoretical simulation method for verification, which verifies the effectiveness of the device of the present invention.
以下结合附图以及实施例,对本发明进行进一步详细说明。应当理解,此处所描述的具体实施案例仅用以解释本发明,并不限定本发明。The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation cases described herein are only used to explain the present invention, and do not limit the present invention.
根据本发明的实施例,如图1所示,提供了一种基于MIMO的激光SAL宽视场成像装置,包括发射系统和接收系统,其中发射系统包含激光源、调制模块、光放大模块、发射光纤阵列和微透镜阵列等。回波信号进入接收系统并与本征光耦合,接收系统包括阵列探测单元和阵列采集成像处理单元等。发射光纤阵列和微透镜阵列组成发射阵列,接收阵列包括阵列探测单元。发射光纤阵列经微透镜阵列准直照射到远场。其中每个发射光纤阵列用于发射激光束,发射的激光束通过微透镜阵列准直照射到远场,以获得大的测绘带宽;回波信号进入阵列探测单元,探测输出信号进行阵列采集成像处理。According to an embodiment of the present invention, as shown in FIG1 , a MIMO-based laser SAL wide-field imaging device is provided, including a transmitting system and a receiving system, wherein the transmitting system includes a laser source, a modulation module, an optical amplification module, a transmitting optical fiber array, and a microlens array, etc. The echo signal enters the receiving system and couples with the intrinsic light, and the receiving system includes an array detection unit and an array acquisition imaging processing unit, etc. The transmitting optical fiber array and the microlens array constitute a transmitting array, and the receiving array includes an array detection unit. The transmitting optical fiber array is collimated and irradiated to the far field through the microlens array. Each transmitting optical fiber array is used to emit a laser beam, and the emitted laser beam is collimated and irradiated to the far field through the microlens array to obtain a large mapping bandwidth; the echo signal enters the array detection unit, and the detection output signal is processed by array acquisition imaging.
根据激光SAL方位向高分辨率和幅宽的要求,设计发射阵列的方位和距离发散角,并确定方位向和距离向多发多收阵列个数。本发明的基于MIMO的激光SAL宽视场成像方法包括如下步骤:According to the requirements of high resolution and width in azimuth of laser SAL, the azimuth and distance divergence angles of the transmitting array are designed, and the number of multi-transmitting and multi-receiving arrays in azimuth and distance is determined. The MIMO-based laser SAL wide-field imaging method of the present invention comprises the following steps:
步骤1)基于目前激光SAL对幅宽的要求,设定3km时幅宽为56.7m,计算得到系统发射的发散角为0.0189rad,根据常用激光器的光纤参数,选择单个输出光源的纤芯直径10μm,光纤数值孔径NA=0.12,采用发射光纤阵列输出激光束形成多发多收的MIMO发射阵列。Step 1) Based on the current requirements of laser SAL for bandwidth, the bandwidth is set to 56.7m at 3km, and the divergence angle of the system emission is calculated to be 0.0189rad. According to the fiber parameters of commonly used lasers, the core diameter of a single output light source is selected to be 10μm, and the fiber numerical aperture NA=0.12. The transmitting fiber array is used to output the laser beam to form a multi-transmit and multi-receive MIMO transmitting array.
步骤2)依据3km探测距离的需求,基于雷达方程和上述阵列发射光束发散角,确定方位向(航线方向)和距离向(斜距方向)多发多收阵列排布方式为阵列,对于上述发射光纤阵列,设计与发射阵列对应的微透镜阵列,微透镜直径为127μm,焦距529μm,间距254μm,如图2所示,将发射光纤阵列一一对应地放置于微透镜阵列的焦面位置,并固定好,发射光纤和其前面对应的微透镜为一个发射阵元,经微透镜阵列后单个发射阵元的发散角θ单为0.0189rad,其中/>,f是微透镜的焦距,d是发射阵元的孔径直径。采用MIMO的阵列间合束模式,多发多收阵列合束激光SAL的发散角为/>。Step 2) According to the requirement of 3km detection distance, based on the radar equation and the above array transmission beam divergence angle, determine the multi-transmit and multi-receive array arrangement in azimuth (route direction) and range (slant range direction): For the above-mentioned transmitting optical fiber array, a microlens array corresponding to the transmitting array is designed, and the diameter of the microlens is 127μm, the focal length is 529μm, and the spacing is 254μm. As shown in FIG2 , the transmitting optical fiber array is placed one by one at the focal plane position of the microlens array and fixed. The transmitting optical fiber and the corresponding microlens in front of it are a transmitting array element. After passing through the microlens array, the divergence angle θ of a single transmitting array element is 0.0189rad, where/> , f is the focal length of the microlens, and d is the aperture diameter of the transmitting array element. Using the MIMO array-to-array beam combining mode, the divergence angle of the multi-transmitter multi-receiver array beam combining laser SAL is/> .
在单个孔径大发散角的基础上,阵列间合束模式可提高视场内能量,增加探测距离及测绘幅宽,阵列激光SAL方位向的分辨率。为使方位向不出现多普勒模糊,单发单收激光SAL的脉冲重复频率PRF满足不等式/>,/>是成像装置沿方位向运行速度。在成像过程中,为了防止距离向模糊,测绘带内的回波信号需要在同一个脉冲重复周期内被天线接收,即距离向测绘带宽/>,c为光速。On the basis of a single aperture with large divergence angle, the beam combining mode between arrays can improve the energy in the field of view, increase the detection distance and mapping width, and the resolution of the array laser SAL in azimuth In order to avoid Doppler ambiguity in the azimuth direction, the pulse repetition frequency PRF of the single-transmit and single-receive laser SAL satisfies the inequality/> ,/> It is the speed of the imaging device in the azimuth direction. In the imaging process, in order to prevent the range ambiguity, the echo signal in the surveying band needs to be received by the antenna within the same pulse repetition period, that is, the range surveying band is wide/> , c is the speed of light.
步骤3)如图3所示,假设带有微透镜阵列的发射系统为二维阵列,阵元数为,M为方位向阵列个数,N为距离向阵列个数,第(m,n)个阵元的坐标为(xm,yn),每个阵元的初始相位为/>,阵元的轴向振幅为/>,远场平面的坐标用光束传播方向角/>来表示,各阵元近似为高斯光束,经过微透镜阵列合成所得的近场光束振幅U(x, y)为:Step 3) As shown in Figure 3, assume that the transmitting system with the microlens array is a two-dimensional array with the number of array elements being , M is the number of arrays in azimuth, N is the number of arrays in range, the coordinates of the (m,n)th array element are (x m ,y n ), and the initial phase of each array element is/> , the axial amplitude of the array element is/> , the coordinates of the far-field plane are expressed by the beam propagation direction angle/> To express, each array element is approximately a Gaussian beam, and the near-field beam amplitude U(x, y) synthesized by the microlens array is:
(1) (1)
其中,i为虚数,ω=63.5μm为经过微透镜阵列后每个发射阵元的光斑半径,exp()为指数运算,(x,y)表示发射阵元的坐标。Where i is an imaginary number, ω=63.5μm is the spot radius of each emitting element after passing through the microlens array, exp() is an exponential operation, and (x, y) represents the coordinates of the emitting element.
步骤4)由多发多收理论,远场光强分布可看作微透镜阵列输出光场的傅里叶变换,多发多收阵列的出射光在远场形成的场分布表示为:Step 4) According to the multi-transmitter multi-receiver theory, the far-field light intensity distribution can be regarded as the Fourier transform of the output light field of the microlens array. The field distribution formed by the output light of the multi-transmitter multi-receiver array in the far field is Expressed as:
(2) (2)
远场光强分布可表示为:Far field light intensity distribution It can be expressed as:
(3) (3)
上式简化为公式(4):The above formula is simplified to formula (4):
(4) (4)
其中,指成比例,/>, />, />,其中/>表示第(m,n)个发射阵元初始相位在x方向分量,/>表示第(m,n)个发射阵元初始相位在y方向分量。in, Refers to proportion, /> , /> , /> , where/> represents the initial phase component of the (m,n)th transmitting array element in the x direction,/> Represents the initial phase component of the (m,n)th transmitting array element in the y direction.
根据上述公式(4)计算出远场光斑能量分布。The far-field spot energy distribution is calculated according to the above formula (4).
步骤5)计算出不同排布方式时的远场光斑能量分布,远场光场总能量分布I总,主瓣能量分布I主,旁瓣能量分布I旁。Step 5) Calculate the far-field light spot energy distribution for different arrangements, the far-field light field total energy distribution Itotal , the main lobe energy distribution Imain , and the side lobe energy distribution Iside .
为实现合束后远场主瓣能量集中度最大,并抑制栅瓣,设置评估函数;In order to maximize the energy concentration of the far-field main lobe after beam combining and suppress the grating lobe, the evaluation function is set ;
其中阵列光束的主瓣能量集中度,其中/>为极坐标系下的光场强度表示,(r, z, θ)为对应的极坐标系下的坐标表示,ω为光斑半径。The main lobe energy concentration of the array beam is , where/> is the light field intensity in the polar coordinate system, (r, z, θ) is the corresponding coordinate representation in the polar coordinate system, and ω is the spot radius.
栅瓣特性的对比度;其中Imax为远场主瓣的能量和总能量的比,k1为主瓣特性的加权值;Cmax为主瓣与最大栅瓣的对比度,即远场主瓣的能量减去最大栅瓣的能量与主瓣能量比,k2为栅瓣抑制的加权值。基于评估函数k1=0,k2=1,以抑制栅瓣为适应函数优化阵元间距,得到阵列发射装置的位置排列方法。Contrast of grating lobe characteristics ; Where I max is the ratio of the energy of the far-field main lobe to the total energy, k 1 is the weighted value of the main lobe characteristic; C max is the contrast between the main lobe and the maximum grating lobe, that is, the ratio of the energy of the far-field main lobe minus the energy of the maximum grating lobe to the main lobe energy, and k 2 is the weighted value of grating lobe suppression. Based on the evaluation function k 1 =0, k 2 =1, the array element spacing is optimized with grating lobe suppression as the adaptation function, and the position arrangement method of the array transmitting device is obtained.
在均匀线阵中,相邻阵元之间的间距相同,相同的位置差会产生相同的相位差,导致等间距的布阵方式会产生栅瓣。基于此,提出稀疏MIMO体制,以此获得最大的雷达有效孔径。下面为发射阵列仿真验证的过程和结果。In a uniform linear array, the spacing between adjacent array elements is the same, and the same position difference will produce the same phase difference, resulting in grating lobes in the array arrangement with equal spacing. Based on this, a sparse MIMO system is proposed to obtain the maximum radar effective aperture. The following is the process and results of the simulation verification of the transmit array.
根据目前应用的需求,设计激光SAL在探测距离3km成像时,方位向分辨率毫米级,幅宽56.7m。考虑单个阵列的发散角为0.0189rad,经过微透镜准直后光斑直径为127μm,阵元间距为254μm。依据此参数,根据方位向分辨率计算公式,单个阵元的方位向分辨率ρ=0.041mm,根据PRF计算公式/>,/>为运行速度。此时PRF=1219.5KHz,此时在3km探测距离处测绘幅宽为56.7m。According to the current application requirements, the laser SAL is designed to have a millimeter-level azimuth resolution and a width of 56.7m when detecting images at a distance of 3km. Considering the divergence angle of a single array is 0.0189rad, the spot diameter after microlens collimation is 127μm, and the array element spacing is 254μm. Based on these parameters, according to the azimuth resolution calculation formula , the azimuth resolution of a single array element is ρ=0.041mm, according to the PRF calculation formula/> ,/> is the running speed. At this time, PRF = 1219.5KHz, and the survey width at a detection distance of 3km is 56.7m.
在不增加脉冲重复频率 PRF条件下,阵列MIMO合束的情况下,在方位向设置4个阵列单元;在距离向设置4个阵列单元,在保持方位向发散角18.9mrad,距离向成像幅宽56.7m不变的情况下,提高成像区域的光场能量。根据此需求,采用表1中的参数进行模拟。Without increasing the pulse repetition frequency (PRF), in the case of array MIMO beam combining, 4 array units are set in the azimuth direction; 4 array units are set in the range direction, and the light field energy in the imaging area is increased while keeping the azimuth divergence angle at 18.9 mrad and the range imaging width at 56.7 m unchanged. According to this requirement, the parameters in Table 1 are used for simulation.
表1Table 1
, ,
接着模拟了多发多收列阵远场光斑分布,所用参数为方位向4个阵元,距离向4个阵元,波长λ=1.550μm,准直后阵列光斑半径63.5μm。模拟所得结果见图4a和图4b所示,图4a显示了远场的二维光场能量分布,图4b为一个维度的光强分布,之后采用优化后的稀疏阵列,二维阵元的位置间隔为(127μm, 254μm, 190μm),模拟所得二维光场及光强分布如下图5a,图5b所示,仿真结果显示,经过优化后,中心主瓣能量集中度增强,栅瓣峰值能量被抑制。Then, the far-field spot distribution of the multi-transmitter multi-receiver array was simulated, with the parameters of 4 array elements in azimuth, 4 array elements in range, wavelength λ=1.550μm, and array spot radius of 63.5μm after collimation. The simulation results are shown in Figures 4a and 4b. Figure 4a shows the two-dimensional light field energy distribution in the far field, and Figure 4b is the light intensity distribution in one dimension. Then, the optimized sparse array was used, and the position interval of the two-dimensional array elements was (127μm, 254μm, 190μm). The simulated two-dimensional light field and light intensity distribution are shown in Figures 5a and 5b below. The simulation results show that after optimization, the energy concentration of the central main lobe is enhanced, and the peak energy of the grating lobe is suppressed.
上述MIMO同时发射相互可分离的光束,发射光束照射到目标后,采用阵列接收的方式,将多通道的回波信号分别接收,并进行信号能量叠加和成像处理,不同的收、发通道组合会形成不同位置的等效相位中心,完成合成孔径激光雷达成像。The above-mentioned MIMO simultaneously transmits mutually separable light beams. After the transmitted light beams hit the target, an array reception method is adopted to receive the echo signals of multiple channels separately, and signal energy superposition and imaging processing are performed. Different combinations of receiving and transmitting channels will form equivalent phase centers at different positions to complete synthetic aperture lidar imaging.
本领域的技术人员容易理解,以上所述仅为本发明的较佳实施例而已,并不用以限制本发明,凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等,均应包含在本发明的保护范围之内。It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
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