Frequency Source Design Based On FMCW Radr System

The properties of microwave and millimeter-wave signals such as short wave length and wide bandwidth are helpful in the military guidance and electronic countermeasures. Frequency-modulated continuous wave radar uses high frequency electromagnetic wave as carrier, and it has become the best choice for short-range targeting radar instead of the ultrasonic and infrared collision avoidance system for its precision targeting capability, the simple transmit waveform, low emission power and sophisticated digital signal processing algorithms. For frequency synthesizer is the key part of the radar system, it determines the performance of the radar system, so it is significant to develop a frequency source with high performance.With the electronic systems’ request for frequency synthesizer increasing, frequency synthesis technology is constantly evolving, and it can be divided into three phases: from the initial direct analog frequency synthesis(DAFS) to indirect frequency synthesis(IS), then to the current the direct digital frequency synthesis(DDS). Conventional FMCW signal is produced by digital devices such as DSP and DAC. They generate linear voltage to control the VCO, while the accuracy, linearity, resolution of the signal generated in this way are quite poor, so this design method has been almost abandoned now. The signal generated by DDS has the features of high resolution, frequency conversion speed, high linearity, small size, and low power consumption, so it is commonly used in the FMCW radar system.This article relies on the projects "E-band automotive collision avoidance radar" and "Ka-band radar of security". Select the "the structure of PLL mixed in loop and mixing DDS outside the ring" as the program design structure after comparing the features of DDS and PLL, the advantages and disadvantages of different structures. The focus of the program is an ultra-low phase noise X-band single-frequency signal generated by the structure of in looping mixer of PLL, since the signal not only severs as the local oscillator of the mixer, it but also serves as a reference clock of DDS(after divided by 4). A X-band FMCW radar frequency source is designed after the accurate calculation of the main parameters of the system and a reasonable selection of major components. The main contents are as follows:Summed up the automotive collision avoidance radar’s research status in the world, and discussed the basic measurement principle.Selected “the structure of PLL mixing in looping and mixing DDS outside the ring” after comparing the traditional structures of continuous wave radar and calculating the parameters.Developed and completed the hardware debugging, and analyzed the problems in the process of debugging and solutions.