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无人机着陆采用微波着陆系统(MLS)作导航系统具有很大优势,针对MLS信号高精度2DPSK解调和AM解调的要求,提出了一种基于FPGA的中频数字化解调方案;分析了改进科斯塔斯环法(Costas)实现载波同步及数字正交AM解调的原理;重点介绍了利用坐标旋转数字式计算机(CORDIC)算法实现数控振荡器(NCO)、鉴相、AM解调关键模块的设计过程。该算法采用流水线结构,只有加法和移位,资源消耗低、效率高、易于FPGA实现。应用VHDL硬件语言进行编程,采用同一电路完成了2DPSK解调和AM解调。仿真结果证明了方案的可行性和准确性,该方案可广泛应用于多种数字中频接收机,具有广阔的应用前景。
UAV landings using microwave landing system (MLS) as a navigation system has great advantages. In order to meet the requirements of high precision 2DPSK demodulation and AM demodulation of MLS signals, a digital IF demodulation scheme based on FPGA is presented. Costas is used to realize carrier synchronization and digital quadrature AM demodulation. The key technologies of NC oscillator (NCO), phase detector and AM demodulator are introduced emphatically. The design process. The algorithm uses pipeline structure, only addition and shift, low resource consumption, high efficiency, easy FPGA implementation. VHDL hardware language programming, using the same circuit to complete the 2DPSK demodulation and AM demodulation. The simulation results prove the feasibility and accuracy of the scheme. The scheme can be widely used in a variety of digital IF receivers, and has broad application prospects.