In this paper, we investigated the frequency modulation continuous wave (FMCW) lidar rang measurement principle, then designed a simulated distance measurement scheme and building the model. Using the OptiSystem system modeling simulation, the relationship between frequency modulation (FM) bandwidth, FM time and rang measurement accuracy is investigated, and the effect of different sweep parameters on the accuracy of the final rang measurement results is discussed in the time and frequency domains. The simulation tests the delay of the target at 30, 60 and 90 meters respectively, and the distance is derived by beating the frequency of the optical echo signal with the local oscillation optical signal and calculating the beat frequency.
To address a technical difficulty of long scanning cycle of broadband (100 MHz~900 MHz) frequency sweep source, an ultrafast broadband sweep source was designed based on the basic principle of direct digital-frequency synthesis (DDS) theory by using the high-performance DDS chip AD9914. During the design, the DSP28335 chip was used as the control device. The designed source can output 100MHz~900 MHz swept-frequency signals and it can realize sawtooth wave frequency-modulated signals in the shortest cycle (8us) by configuring the digital ramp generator in the chip. Moreover, a microstrip stepped impedance low-pass filter was designed using ADS to eliminate spurious signals in the direct synthesizer and decrease the in-band attenuation, thus making the curve flatter. According to final test and experimental data analysis, the designed sweep source has a large output broadband, short sweeping cycle and strong inhibition of spurious signals. It possesses great application values.
In this paper, the distance information is obtained according to the relationship between distance and beat frequency in FMCW ranging principle, the ranging process of sawtooth wave as frequency modulation signal is described in detail, and the causes of ranging error are analyzed briefly. The distance measurement system of simulation uses Matlab software to write, and the hardware ranging platform is built by DB77M24A6426V2 millimeter wave radar module. It is verified that the distance measurement system design in this paper achieves more accurate ranging in the short distance measurement, and provides a relatively simple ranging waveform, which provides a relatively powerful reference basis for the subsequent ranging system design and hardware selection.
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