# Theory and Design of Blink Jamming
## 4 Designing Formation Jamming Techniques
### Sinusoid Modulated Blink Jamming  
A variation of blink jamming was examined in order to evaluate a possible weakness in the monopulse system. This was the application of a sinusoidal amplitude modulation on the blink waveform, shown in Figure 22. The impact of this waveform is particularly evident in the error signal at the output of the monopulse receiver shown in Figure 23. As the two jammers hand-off and the power levels drop close to zero the angular error spikes, in some cases well above the \(\pm 30^{\circ}\) shown (the vertical axis were limited in the figure to capture the more detailed effects).  
Figure 21: The miss distance, defined as the distance between the tracking point at the target range and its actual location, for targets \(A\) and \(B\), as well as their average.  
Figure 22: The jammer blink waveforms from sources \(A\) and \(B\) operating at a 4 Hz and 180\({}^{\circ}\) out of phase with a sinusoidal amplitude modulation applied.  
The effect of this impulse in the tracking system is demonstrated in Figure 24 where, despite the filtering effects of the tracking system, the antenna is pulled off the targets at 2.4 s. While it locks back on to the centroid of the two sources over the next 1.5 s this kind of \"break-lock\" action is the goal of most electronic attacks against tracking radars.  
Understanding this effect and how it is created inside the radar receiver does not make it easy to predict due to the random behaviour of the noise. This differentiation in performance between blink jamming and its modulated version is best illustrated in Figures 25 and 26. In both figures the same jamming scenario is repeated with the two different waveforms while the natural frequency of the tracking loop and the blink frequency are swept over a range of values. In  
Figure 23: The azimuth error signal from the monopulse receiver when a sinusoidal amplitude modulation is applied to the blink jamming signal.  
Figure 24: The miss distance, defined as the distance between the tracking point at the target range and its actual location, for targets \(A\) and \(B\), as well as their average during a sinusoidal amplitude modulated blink jamming attack.  
blink jamming attack shows a stable miss distance over a range of scenarios, tracking the mid-point of the two jammers except in cases of the natural frequency being too low, or the blink frequency simply not pulling the tracking system back-and-forth fast enough (the 600 m miss distance is indicating its actually tracking one of the targets that are separated by 600 m).  
The effects seen in Figure 26 for the average miss distance of the amplitude modulated attack are very different, requiring a scale in dB-meters in stead of meters. Break-lock events can be seen occurring over a range of values causing large increases in miss distance compared to the more typical tracking point between the two aircraft.  
Unfortunately the random nature of this break-lock event makes it a feature that cannot be designed to occur at specific times. However despite its random nature, even if it does not occur it still causes a miss distance equal to or greater than that of the unmodulated blink attack.  
Figure 25: The average miss distance during a set of engagements with varied antenna angle tracking response frequencies and blinking frequencies using a square wave.