Effectiveness of FM CW jammer parameter on break-lock condition of phase locked loop in monopulse receiver

In this paper, the break-lock phenomenon of phase locked loop (PLL) in missile borne monopulse radar receiver is presented. The continuous wave (CW) frequency modulated (FM) signal is used as jamming signal which is injected into the PLL along with the desired radar echo signal. The effects of key parameters in the FM CW jammer platform such as frequency sensitivity (k_f), modulating signal amplitude (v_m) and modulation frequency (f_m) on break-lock are reported. The value of k_f at which the PLL loses the frequency lock to the radar echo signal as a function of modulating signal amplitude and modulation frequency is presented. It is shown that break-lock is achieved at 3.511×10⁹ Hz/V for a typical modulating signal amplitude of 5 mV and modulation frequency of 200 kHz, when the radar echo amplitude at the PLL input is 1 volt. The break-lock is also studied by injecting radar echo signal with different amplitude at the PLL input and the value of k_f required for break-lock is reported. From these results, the frequency deviation and modulation index required for break-lock are computed and conclusions are demonstrated. The PLL with a third order passive loop filter is designed by exact method and simulation is carried out using visual system simulator (VSS) AWR software for performance evaluation.