改进Costas环的GPS载波跟踪环路

Design and Implementation of Improved Carrier Tracking Loop in High Dynamic Circumstance

针对高动态环境下载波信号会产生较大多普勒频移而导致跟踪环路失锁的问题,对其基带信号进行双向限幅以改进Costas环的鉴相特性。同时,采用叉积型鉴频器,通过频率牵引使捕获后的频差达到跟踪模块的工作范围,并根据对锁相环和锁频环的特性分析及其各自的优缺点,选择锁频环辅助锁相环的复合结构。仿真试验结果表明,在高动态环境下(运动速度1 200 m/s)该跟踪环可以快速跟踪卫星信号,即时误差趋近于0,且当加速度达到40 g以上时,经过该复合环跟踪后的多普勒频移比传统锁相环减小了50%以上。

According to the problem of lost lock of tracking loop caused by the larger Doppler frequency shift in high dynamic circumstance,the phase characteristics of Costas loop is improved through the bidirectional limiter to its baseband signal. Meanwhile,cross product frequency discriminator is chosen,and through frequency pulling so that it makes frequency difference captured reaches the work scope of tracking module. Then,in view of the characteristics of the phase-locked loop and frequency-locked loop choose the composite structure of the frequency-locked loop auxiliary phase-locked loop. It shows that the tracking loop can quickly track the satellite signal in high dynamic circumstance,and the instant error approaches 0,and when the acceleration reached more than 40 g,the Doppler frequency shift through the composite loop is reduced more than 50 % than the conventional phase-locked loop.