Frequency Estimation of Uncooperative Coherent Pulse Radars

RF Frequency estimation is required in many applications, such as Radar Electronic Warfare (REW) and telecommunications. For example, passive location estimation of uncooperative radar sites in a target area is an important military application and can be achieved by measuring the Doppler-shifted frequencies of trains of modulated pulses received by an Electronic Support Measure (ESM) receiver on-board of a moving platform such as an aircraft or Unmanned Aerial Vehicle (UAV). The accuracy of the location technique depends on the accuracy of Doppler frequency measurements. There are several techniques that can be used to estimate accurately the frequency of continuous wave signals. However, estimating the frequency of trains of modulated pulses is more challenging because the pulse durations are very short. Furthermore, the computational complexity required for accurate estimation may become impractical if the Pulse Repetition Frequency (PRF) becomes small. In this paper, an FFT-based approach is considered. Techniques to improve the frequency step size, such as the Zoom FFT technique and the secant method, will be presented. Simulation results show that the frequency estimation approaches presented here can closely approach the Cramer-Rao Lower Bound (CRLB) in most cases.