Design Of Synthetic Aperture Lidar Transceiver System

Synthetic aperture lidar is a result of applying the traditional synthetic aperture radar technology in the laser band,which has an important application prospect in the field of airborne SAL high-resolution imaging to the ground.At present,the maximum resolution that a synthetic aperture radar using a microwave wavelength signal can achieve is far less than that of a lidar system,while an ordinary lidar reuqires a large optical aperture receiving lens to achieve the purpose of high-resolution and long-distance imaging.Limited by factors such as the size of the radar system,this paper uses a combination of the two methods to build a complete set of synthetic aperture lidar transceiver system by using a large bandwidth laser emission signal with good coherence.Specifically,the related research content and work of this paper mainly include the following aspects:First of all,the overall design of the synthetic aperture lidar transceiver system is proposed.This part introduces the basic principle of linear frequency modulation continuous wave(LFMCW)lidar technology and it’s range resolution.And it focuses on the principle of laser signal heterodyne detection technology used in the system,detection and reception conditions,and the noise analysis in the reception,etc.This solution can overcome the problem of long-distance weak echo signal information extraction and greatly improve the detection sensitivity of the system.Secondly,according to the relationship between the parameter design and the structure of the traditional photoelectric phase-locked loop system,the design scheme of the photoelectric phase-locked loop in this paper is proposed,and the design steps of the loop filter element parameters are given.In addition,in order to generate a large-bandwidth chirp laser emission signal,the current drive signal of 1550 nm DFB semiconductor laser is predistorted based on the current drive circuit,which overcomes the defect of nonlinear frequency of the output signal of semiconductor laser.At the same time,by designing the optical heterodyne lens and the PIN photodiode signal receiving and conditioning circuit,the system achieves effective coherent reception and condition of the weak echo laser signal and the reference laser signal in the system.Then,based on the current driving circuit of the semiconductor laser,we complete the hardware design of the laser emission board,which is mainly controlled by FPGA,powered by independent power supply,and including DAC,DDS and trans resistance amplifier circuit.By optimizing the layout of the key chips and the routing design of important signals in the transmitter board,the harmful phenomena such as signal coupling and crosstalk are avoided,so as to ensure the effectiveness of current driven signal compensation processing.In addition,the design and debugging of the FPGA program on the laser emission board is completed.Finally,the high resolution synthetic aperture laser radar transceiver system is built by using the laser emission board,optical heterodyne detection transceiver lens and laser receiver board.Through experiments,the system generates a 20 GHz bandwidth chirp laser emission signal,which can achieve the best 11.1mm range resolution under the condition of 90% reflectance of the test target in the range of 20 m.