Research On Direction Finding Techniques In Passive Radar Seeker

The techniques of direction finding in PRS(Passive Radar Seeker) is mainly studied, including widening direction finding bandwidth, analyzing the direction finding measurement performance of the PRS with radar decoy, improving the anti-decoy ability and the direction finding performance to complicated radar signals of the PRS. Soft and hardware implement of some parts of the subject is carried out in the practical system, and the experiments prove these proposed methods valid and effective, and some indexes are tested in the system.In order to widen the direction finding bandwidth of the PRS, an ordinal ambiguity resolution method based on virtual short baseline is proposed. It solves the contradiction between the maximal unambiguous angle and direction finding bandwidth. The shortest baseline can be longer than the half-wavelength of the incident signal, and the length of the baselines can not be stagger. It can realize direction finding in a larger bandwidth in condition of limit size of PRS, having no use for more antennae and direction finding accuracy reducing. The method is very practical.The SNR limitation and channel phase consistency condition of solving ambiguity correctly is proposed. The correctness of the theoretic analysis is effectively demonstrated by computer simulation and experiment data.Considering the interference of the radar decoy, the angle measurement performance of amplitude-comparison PRS is studied. The angle measurement mathematical model of phase-comparison PRS with the effect of active decoy is derived and analyzed in detail. It shows that the phase-comparison PRS couldn't distinguish radar and decoy, the PRS will trace the synthetical phase center of the radar and decoy, the tracing angle is uncertain and changed continually. The phase-comparison PRS based on monopulse can't trace the correct target with the effect of the radar decoy. Both the simulation result and the experimental data confirms the correctness of the theory.Using spatial spectrum estimation direction finding technique in PRS, which exploiting the super-resolution property of the spatial spectrum to reduce the resolution angle of the PRS, can distinguish radar and decoy under a certain distance, consequently realize the purpose to attack radar. On the basis of traditional MUSIC(Multiple Signal Classification)algrithm, considering the power and correlation property between radar and decoy, an improved subspace DOA(Direction of Arrival) estimation method which using the invariance property of noise subspace is proposed. Compared to traditional MUSIC algorithm, this new method not only has better resolution in condition of closely spaced sources, but also has superior performance in case of sources with power difference or partially correlation. PRS using this new method can distinguish radar and decoy with good performance.The subspace algorithm based on time-frequency distribution which uses the time, frequency and spatial domain information of the source sufficiently, has good source selectivity and noise reduction ability. Its performance is superior to traditional MUSIC algorithm. On the basis of STFD-MUSIC(Spatial time-frequency distribution-MUSIC) algorithm, a weighted averaging STFD-MUSIC algorithm is proposed. The weight enhances the effect of high power time-frequency point. The noise term reduces and the noise is more suppressed.Theoretic analysis and simulation result shows that the weighted time-frequency averaging STFD-MUSIC algorithm has superior performance compared to time-frequency averaging STFD-MUSIC algorithm, which can realize the 2-D DOA estimation robustly.