What is the principle of cross-eye jamming and how does it create angular deception?

The principle of cross-eye jamming creates angular deception against a monopulse tracking radar by transmitting two coherent signals from two spatially separated antennas on the target platform, with the signals carefully phased so that the radar's monopulse angle measurement system is deceived into measuring an incorrect angle of arrival, pointing the radar beam away from the true target. Cross-eye jamming works because monopulse radars determine target angle by comparing the signals received in two antenna half-beams (sum and difference channels). The ratio of the difference to the sum signal gives the target angle. Cross-eye jamming generates an apparent phase center that is displaced from the physical midpoint of the two jamming antennas by creating a specific phase relationship: the two jammer antennas transmit signals that are approximately 180 degrees out of phase, creating a wavefront that has a phase gradient opposite to what the radar expects from a point source. This causes the monopulse processor to calculate an angle of arrival that points away from the true target, potentially outside the physical extent of the platform. The angular deception is: theta_error approximately (d / lambda) x (1 / (SNR x sin(theta_baseline))), where d is the separation between the two jammer antennas and theta_baseline is the angle between the radar line of sight and the jammer baseline. Cross-eye is effective against monopulse radars (which are resistant to amplitude-based deception techniques like inverse gain jamming) because it exploits the phase-based angle measurement mechanism, and is considered one of the most challenging ECCM threats for monopulse radar designers.