Effectiveness of Repeat Jamming using Linear FM Interference Signal in Monopulse receivers

Abstract

Abstract Monopulse technique is widely used in modern tracking radars and missile seekers for precise angle (frequency) tracking. In this paper, the break-lock behavior of phase locked loop (PLL) in monopulse radar receiver in presence of linear frequency modulated (LFM) repeater jamming signal is presented. The radar echo and LFM signals are injected into the PLL simultaneously with an assumption that initially, the PLL locks onto the echo signal frequency. The frequency deviation required for breaking the frequency lock as a function of jamming signal power and modulation rate is reported. The results show that break-lock is achieved at frequency deviation of 0.35 MHz for a typical jammer power of -14 dBm and 200 kHz modulation rate when the radar echo power at the PLL input is -14 dBm. The break-lock is also studied for different modulation rate (200, 300, 400 kHz and so) and echo signal power (-14, -10 dBm) at the input of the PLL. For the computer simulation, the radar echo and centre frequency of LFM signals are assumed at an intermediate frequency (IF) of 50 MHz such that the LFM signal closely replicate the actual radar echo signal. The PLL containing charge pump phase detector and passive loop filter is designed with a typical bandwidth of 200 kHz. The simulation is carried out using visual system simulator AWR software and potential conclusions are demonstrated.