| Compared with pulsed radars,millimeter-wave frequency modulated continuous wave radars have many advantages such as smaller volume,lower emission power,higher range resolution and stronger anti-interference ability.But they are not widely used for various reasons,the most fundamental problem which restricts their development is signal leakage.In this regard,national experts put forward a lot of solutions,the most potential is the RF cancellation technology.This paper studies open-loop RF cancellation system and closed-loop adaptive RF cancellation system respectively.Firstly,the working principle,merits and shortcomings of FMCW radar are introduced,and several methods to solve the problem of signal leakage are proposed.Then,the basic idea of RF cancellation technology is expounded,the concept of cancellation ratio is put forward,and several implementations of RF cancellation technology are introduced.The model of closed-loop adaptive cancellation system is analyzed.Based on this,the open-loop cancellation scheme and closed-loop adaptive cancellation scheme are designed respectively.The cancellation conditions and system delay of the closed-loop system are analyzed.The HFSS software is used to simulate the passive components of the quadrature fundamental frequency mixer of the error detection module and the I-Q vector modulator of the feed-through module.The Schottky diode MS7621 is used for the mixer,the PHEMT tube EC2612 is used for the I-Q vector modulator,and the circuit diagram of the control module is designed using the operational amplifier OP37.Based on the KBR system of the laboratory,the open-loop cancellation system is tested.The test results show that the open-loop system can provide 15dB cancellation ratio.The ADS software is used to simulate the closed-loop adaptive cancellation system,and the simulation results show that the closed-loop system can achieve more than 25dB cancellation ratio.Finally,the work of this paper is summarized. |
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