Monopulse radar analysis for cross-polarisation jamming

Abstract

Cross-polarisation jamming is an electronic attack (EA) jammer that takes advantage of the design weakness in the radar antenna. The monopulse antenna with symmetric antennas in the four quadrants and feed symmetry has Condon lobes in its cross-polarisation signal component. The peaks of the Condon lobes are in the ±45◦ and ±135◦ diagonal planes. The cross-polarisation jammer receives the tracking signal from the tracking radar, interchanges the polarisation components, and re-transmits it to the tracking radar. If the jammer has a high JSR, the tracking radar will be forced to use one of the Condon lobes as the tracking lobe. Six monopulse antennas are analysed for cross-polarisation jamming. The jammer’s effects on the radar’s angle tracking accuracy are analysed as the JSR increases. How the antenna polarisation purity affects the effectiveness of cross-polarisation jamming is investigated. How the jammer's polarisation inaccuracy affects its ability to induce angular tracking error is investigated. The simulated results are validated using the measurements of the manufactured antenna. The cross-polarisation jammer can induce angular tracking error, but needs high polarisation accuracy. The mathematical models of the antenna cross-polarisation patterns are derived using three different approaches. These models are used to theoretically analyse cross-polarisation jamming and compare the results with the Feko simulations and measurement results.

The axial symmetry in antennas causes Condon lobes in their cross-polarisation component. Two antennas with axial symmetry will have two Condon lobes, while four antennas located in four quadrants with axial symmetry will have four Condon lobes in each quadrant. One of the six antennas was used to validate the axial-symmetry effect on the Condon lobes. The analysis shows that the antenna radiating elements must be symmetrical, and the feed network must be symmetrical to result in symmetrical Condon lobes. The size of the Condon lobes is influenced differently in different antennas. The focal-length-to-diameter (F/D) size influences the Condon lobes in the parabolic reflector antennas. To investigate the effects of F/D size on the Condon lobes, a parabolic reflector antenna with different F/D sizes is designed and analysed. The analysis shows that increasing the F/D reduces the Condon lobes and increases the polarisation purity of the antenna.