瞬时测频系统的线性调频信号分析及改进

频率是雷达信号的关键特征之一，雷达告警(RWR)/电子支援（ESM）等电子战接收机多采用瞬时测频（IFM）技术来实时提取；线性调频（LFM）信号是一种重要的、雷达广泛应用的信号类型，但传统IFM无法检测LFM信号频率特征。提出一种新的基于改进IFM系统的LFM信号特征检测方法，基于IFM系统工作原理建立了LFM信号经过IFM系统的数学模型，并探讨了IFM系统对LFM信号检测的频率分辨力和最小可检测调频斜率。改进IFM系统采用整形检波信号作为采样有效指示信号，以提取LFM信号的到达时间（TOA）和脉冲宽度（PW）；采用模数转换器（ADC）代替传统IFM的极性量化器对其正交通道输出进行连续采样，再通过解模糊、线性回归算法平滑去噪，估计出LFM信号的载频和调频斜率。仿真实验结果表明，改进IFM系统可在一个LFM脉冲内以较高的精度提取LFM信号特征，并保留了传统IFM系统的原有优点。

Analysis of LFM Signals and Improvement of IFM System

Frequency is one of the key features of radar signals, which is extracted in real-time by an instantaneous frequency measurement (IFM) system in electronic warfare receivers used for RWR/ESM. Linear frequency modulation (LFM) signal is an important signal type and used widely in radar, and its frequency characteristics could not be detected by traditional IFM system. A novel technique is proposed based on improved IFM system for LFM signal feature detection, and a mathematical model of LFM signal passing through IFM system is established based on the operating principle of IFM system. The frequency resolving capacity and the minimum detectable frequency modulation slope are discussed. In the improved IFM system, a phasing detector signal is used as the effective indicating signal of sampling to extract the time of arrival (TOA) and pulse width (PW) features. The analog-digital converters (ADC) instead of polarity quantizer of traditional IFM system are used to sample continuously the outputs of the orthogonal channels. The fuzzy clearness and linear regression algorithms are used for noise smoothing and evaluating the carrier frequency and the frequency modulation slope of LFM signal. Simulation results show that the improved IFM system could extract the LFM signal features in an LFM pulse with higher accuracy, and retains the advantages of original IFM system.