由于孔径渡越问题,宽带信号的波束形成需要进行时延处理,传统的数字分数时延波形产生方法是在时域上使用分数时延滤波器。目前,大多数宽带发射波束产生的研究均针对线性调频信号,而对于信号特性更复杂且脉压性能优秀的非线性调频(NLFM)信号研究甚少。文中提出了一种宽带NLFM数字分数时延波形的产生方法,并对该信号实现了发射数字波束形成。首先,将时延分为整数时延和分数时延,利用指数多项式拟合处理得到宽带NLFM信号的时域表达式;然后,通过提取参数的方法在直接数字合成器中直接产生分数时延波形;最后,经过整数时延形成宽带NLFM发射波束。仿真实验证明:各阵列单元产生了宽带时延NLFM波束,发射波束的合成方向良好,没有明显失真,时延方法导致的时延误差远低于传统的滤波器方法,且功率合成效率损失可忽略不计,该方法计算简便,对硬件要求不高。

Due to the aperture crossing problem, beamforming of broadband signal needs time delay processing. The traditional method of digital fractional delay waveform generation uses fractional delay filter in time domain. At present, most researches on broadband transmitting beam generation are focused on linear frequency modulation signal, while few researches on nonlinear frequency modulation (NLFM) signal with more complex signal characteristics and excellent pulse pressure performance. In this paper, a broadband NLFM digital fractional delay waveform generation method is proposed, and digital beamforming is implemented for the signal. Firstly, the time delay is divided into integer time delay and fractional time delay, and the time domain expression of the broadband NLFM signal is obtained by exponential polynomial fitting. Then, the fractional time delay waveform is directly generated in direct digital synthesizer by extracting parameters. Finally, the broadband NLFM transmitting beam is formed by integer time delay. The simulation results show that each array element generates a broadband delay NLFM beam, and the beam synthesis direction is good without obvious distortion. The time delay error caused by the time delay method is far lower than that of the traditional filter method, and the loss of power synthesis efficiency can be negligible. The method is simple to calculate and requires little hardware.

TN957.51