# Theory and Design of Blink Jamming
## 1 Introduction  
Blink jamming is a technique which has been documented as far back as the 1970s for inducing angle errors in tracking radars [1]. However, its understanding has remained limited since that time, as researchers have pursued other mechanisms for countering monopulse radars. Despite this, it offers tantalizing benefits to the Electronic Warfare (EW) engineer in creating a miss distance during missile engagements. Specifically, prior research has not established a theoretical understanding of blink jamming's operation, and its influence on a monopulse seeker, or validated the study of blink jamming in any way. This paper seeks to provide a theoretical understanding of blink jamming, incorporating effects such as skin return and jammer power, the model was then implemented using Field Programmable Gate Arrays (FPGA) and hardware-in-the-loop simulation to validate this framework against a modern threat. This modelling architecture is then used to explore a novel method of blink jamming, and understanding their the factors affecting their design. Monopulse antenna systems have seen wide spread use since the 1970s in tracking radars for air defence systems and airborne missiles [2]. Prior to the advent of monopulse, variants of lobe-on-receive only (LORO) and conical-scan-receive-only (CSRO) were the principle forms of angle tracking in radar systems. LORO and CSRO used a moving receive beam around a fixed transmit antenna to track the angle to a target [3], shown in Figure 1, comparing the received signal amplitude from the beam positions to determine the pointing error. Unfortunately these systems have several downsides, particularly from an electronic warfare (EW) perspective, due to the fact they require multiple pulses from different positions to measure the angle to a target. This leaves them vulnerable to a highly effective form of angle deception using an amplitude modulated signal to replicate the return from a target at an incorrect angle [4, 5]. Monopulse systems were a significant improvement over LORO and CSRO, by using four or more receivers to create multiple simultaneous antenna beams, shown in Figure 2. These beams were typically created with a parabolic dish by off-setting the feedhorns from the focal point, doing so forced the beams slightly off bore-sight, known as beam squint. The resulting antenna patterns could then be used in multiple ways, summing them to create a beam at boresight for transmitting, and using the relative difference in the azimuth and elevation planes to determine the angle to target with as little as one pulse, hence the name monopulse. From a military perspective monopulse antennas were adopted for tracking radars due to their accuracy and protection against angle deception attacks [1]. Unfortunately for EW engineers, it is difficult to create errors in the estimated angle for monopulse systems, which are critical to affecting large miss distances in missile engagements. The existing solutions include cross-eye and cross-polarization jamming, both of which require complex jammer architectures and high jammer-to-signal ratios to be effective [7]. In the case of cross-polarization jamming, the orthogonal polarization of the incident signal must be generated, and it must be done with a high level of polarization purity to distort the monopulse response curve. Cross-eye jamming creates a distortion in the phase-front, through the use of an antenna array that retransmits the incident signal with a 180\({}^{\circ}\) phase reversal. This change in phase is difficult to create precisely over a large bandwidth. In both cases the use of these techniques is often restricted to naval platforms against anti-ship missiles, where the engagement geometry is often limited to a narrow plane. An alternative to the problem of deceiving monopulse systems is to utilize two jammers simultaneously, referred to here as formation jamming, combining their signals in the monopulse receiver in a manner that creates either increased measurement error or jamming controlled indicated angles.