| FMCW (Frequency Modulated Continuous Wave) radar system with non-contact, low power, high accuracy and high range-resolution, is widely used in cabin, oil tanks and other liquid level measurement. In the future it may be applied to other short-range, high-precision measurement field. For close range applications, ranging accuracy will be affected by antenna beam width, the angle between antenna normal direction and reflective surface and other factors. There is no mature and general theory which can be used to analyze the reflection characteristics of electric wave in near field. This paper aims to study the close range reflection characteristics of FMCW radar waves through experimental approach. The main work of the thesis is as follows:The first part of the thesis improves the FMCW radar ranging system based on FMCW RF module with 9.25GHz-10.75GHz frequency range and DSP. According to the study on the characteristics of short-range reflection, the filter amplifier module, A/D module, CPLD module and the control algorithm were improved, and the circuit design, circuit board weld and debugging were completed.Since there are reflex DC component and low-frequency component at the connector between FMCW RF module and the antenna, the filter’s suppression of DC and low-frequency component is limited when experimenting on near-field and the frequency of beat-note signal is relatively low. According to the characteristics FMCW radar ranging system, the second part of the thesis propose a method that decrease the sweep period in order to increase the frequency of the echo signal, and then increase the lower cut-off frequency of the band-pass filter. There are mainly three methods to decrease the sweep cycle:to transmit frequency control sequence through look-up table; to increase the clock frequency of DSP McBSP sampling rate generator to shorten the transmission time; to write interrupt service routine with assembly language.It has been found that there are obvious fluctuations of the amplitude of the echo beat-note signal within a sweeping cycle. Through direct measurement of FMCW RF module emission waveforms by oscilloscope with 12GHz analog bandwidth, the existence of parasitic amplitude modulation in the FMCW signal emitted by radar module has been verified. In the third part of the thesis, a simulation is designed to analysis the influences on range estimation of parasitic AM to range estimation algorithms. It has been verified that the parasitic amplitude modulation results in a larger deviation by comparing with the measured signal. The amending method for correcting the range estimation error caused by the parasitic amplitude modulation is also given.The final part of the thesis presents two short-range experimental testing. In the first experiment, a round reflector panel was cut into rings with the same width, and the echo signal characteristics of different rings are measured under near-field antenna beam irradiation. In the second experiment, the entire round steel panel was used as reflecting surface. By adjusting the angles between the reflecting surface and antenna’s normal direction, the echo signal characteristics of different angles are measured and the analyzed. It is also found that when the reflector is rotated to a certain angles, second-round reflection between the antenna and the test reflector can be observed. The generation mechanism is analyzed. |
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