Experimental and Simulation Analysis of Break- Lock in Phase Locked Loop Synthesizer for Frequency Tracking Applications

Modern missile seekers invariably employ monopulse radar with phase locked loop (PLL) as a frequency (angle) tracking subsystem in the receiver. The frequency locking and/or unlocking of these receivers can be achieved either by introducing imperfections in the monopulse design or using multiple repeater sources. In the present paper, the break-lock of PLL synthesizer in the monopulse radar receiver is presented. The linear frequency modulated (LFM) signal has been used as a repeater interference signal, which is injected into the PLL along with radar echo signal. The frequency deviation as a function of LFM signal power required to break-lock is presented for different values of modulation rate and echo signal power. The simulation results show that breaklock is achieved at frequency deviation of 0.36 MHz (0.35 MHz measured value) for a typical jammer power of -14 dBm and modulation rate of 200 kHz with radar echo signal power of -14 dBm at the PLL input. The measured results show that at a typical jammer power of -14 dBm, break-lock is achieved at frequency deviations of 0.35 and 0.9 MHz for modulation rates of 200 and 500 kHz respectively, revealing that at lower values of modulation rate, breaklock is achieved at lower values of frequency deviation. The computer simulation is carried out for performance prediction and experimental measurement results are presented in support of the simulated results. With fairly good and consistent agreement between the measured and simulated results, the PLL is well suited to be integrated within monopulse radar receivers for LFM jamming.