Design Of Guidance Laws Against Targets With Towed Decoys

On modern battlefields, radar and electronic warfare is becoming more and more important. A jajor part of the warfare is the engagement of air-to-air missiles against aircraft targets. For aircraft targets, towed decoy technology is introduced to implement effective electromagnetic interferences on the missiles. In a typical usage, an active decoy is towed via a rope by the target aircraft. The decoy is capable of emitting the signal, same in type as, but stronger in magnitude than the signal of the aircraft, so that the missile cannot distinguish easily the real target from the decoy. Generally, the missile will aim at and eventually attack the decoy instead of he target aircraft. How to improve the missile’s ability of attacking the aircraft with a towed decoy is a very important research topic. In this thesis, the topic will be considered, and the main contents are as follows.First, for an aircraft with a towed decoy, essential principles of electromagnetic interferences are introduced, then analysis is conducted on the advantages, disadvantages, and the selection of some important parameters such as the length of the towing rope. Gauss-Euler equations are used to establish the aircraft-decoy’s kinematic model from the total energy point of view, thus the internal forces of the system can be conveniently ingored in modeling.Second, coordinate systems used in the thesis are introduced, together with the transformation among them. Guidance process of the missile is analyzed, and the kinematic model of the missile and the target is constructed, where the respective accelerations of the missile and the target are taken as control and external disturbance variables. The the calculation of the miss distance is discussed, and the calculation process in the simulation is given. Based on relative models of the missile versus the decoy and of the decoy of the target aircraft, the relative model of the missile versus the target aircraft is constructed.Third, based on the relative kinetics, the line-of-sight rate of the missile and the target aircraft, which is of interest in guidance law, is estimated based on the ling-of-sight rate of the missile and the decoy, which available from measurement. Based on the line-of-sight rate estimation, proportional navigation guidance is used to the missile guidance law design, and the simulation is conducted. The simulation takes into account the variations of parameters, such as the navigation ratio, missile-target velocity ratio, and target maneuvers. The effects of these variations on the miss distance are analyzed. Simulation results justify the feasibility of line-of-sight rate estimation algorithm and the proportional navigation guidance design for the guidance of the missile against the target with a towed decoy.The last, taking advantage of the decoy’s conical blind zone in interference, head-pursuit interception is used in guidance law design. In head-pursuit interception, the missile is able to eventually enter the blind zone, thus the interference of the decoy is avoided. Simulation is conducted on the designed guidance law, and simulation results verify the feasibility of the guidance law against tragets with towed decoys.