Reseach On FMCW Radar RF Cancelling System And Baseband Design

In recent years, with the development of microwave devices and digital signal processing technology, CW radar system is attracting more and more attention for its irreplaceable advantages. For example, 77 GHz automotive collision avoidance radar system, in these applications, restricted by measuring accuracy and the cost the transmit signal is all LFMCW. However,One of the greatest problems facing designers of CW type radars is that of achieving sufficient isolation between transmitter and receiver. In order to solve this problem, many scholars have carried out a long time research. On the basis of these achievements, we put forward a kind of digital closed-loop adaptive RF cancellation architecture based on DSP + FPGA, it is better avoid dc drift in the analog circuit by a Super-heterodyne architecture.The theoretical analysis, cancellation algorithm simulation, system level simulation, DSP implementation and the final system test for this digital cancellation scheme is introduced in this paper. Firstly, in the basis of adaptive cancellation principle and adaptive algorithms, two different adaptive cancellation algorithms of simulation are carried out for the reason of different amplitude and phase control in the engineering realization. The simulation results of these two control methods show that for different signal input they all have a good suppression for the leak signal. Secondly, the cancellation depth, cancellation bandwidth and stability of the closed-loop for the digital adaptive RF cancellation system are analyzed, which have an important guiding for the hardware implement of the project. In the last, a system is built in Agilent’s ADS, in order to identify system performance for the LFMCW signal. Finally, a detailed for the while baseband system including: data flowing, the selection of the hardware parameter and the implementation of fixed point algorithm of DSP are introduced, all these are in order to meet the time requirement of baseband.After finish the system software and hardware, a hardware test about the adaptive cancellation system in the x-band(9.29GHz-9.59GHz) is operated. Test results showed that: In the case of static single frequency, the hardware can achieve a cancellation about 30 dB over the entire bandwidth. In the case of dynamic frequency sweep: 30MHz/ ms、 60 MHz / ms and 100 MHz / ms, the cancellation depth can also reach 10-20 dB. In the last, the results achieved as well as problems appear in the paper aresummarized, which point the direction of our future work.