Research On Adaptive Interference Rejection Algorithm For Wideband Phased Array Radar

Wideband phased array radar is widely used in military and national defense, national economy, scientific research and other fields, because of its high resolution, target classification and recognition, fast electrical scanning, adaptive clutter suppression, the detection and tracking of dense targets and monitoring of long-range spatial ability. However, owing to the complex electromagnetic environment, the wideband phased array radar is threatened by malicious interference. This dissertation studies the adaptive interference suppression algorithm for wideband phased array radar. In this dissertation, some of the research contents and conclusions are as followsStart from the construction of wideband phased array radar signal model and interference model, this dissertation studies the space-frequency beamformer and the space-time beamformer which is suitable for the wideband phased array radar. Then, how many degrees of freedom(DOFs) needed to restrain wideband jammer and what is the influence of wideband jammer or space-time structureto the beam are studied. The influence to the performance of interference rejection is analyised with the factors corresponding to array structure, beamformer structrue or interference. Finally, in order to decrease the DOFs or dimensions in temporary, a high efficient wideband beamformer with only half temporary tap number is proposed.First, to avoid the aperture fill phenomena, wideband phased array radar is modeled by time delay. Fractional delay filter is introduced to control the beam pointing direction and is used to model the wideband array jammer.Next, the wideband space-time or space-frequency beamformer can suppress the wideband interference signal by increasing the DOFs in time domain or frequency domain. This dissertation studies the problem of wideband jammer rank estimation which refers to the number of DOFs needed to barrage jammers. The closed form for single wideband jammer rank estimation is proposed by the thought of transforming frequency to angle, then this ideal could be extended to the case of two jammers or multiple jammers. Simulation results verify these closed forms for wideband jammers’ rank estimation. Besides, the effect of wideband jammer to the beam pattern and how the time-space beamformer could reduce its effect are studies, which also verifies the factors of wideband jammer rank estimation, including jammer angle, element number and ratio of bandwide and carrier frequency.Then, in addition to these three factors, the tap number of delay line is also a important factor. This dissertation studies the effect of these factors to the performance of anti-jamming, then an upper bound of the performance of signal to interference plus noise ratio(SINR) is derived with the increase of the number of taps in the time domain, and it is verified by simulations’ s results. The effects of different tap numbers after different element are studied. Results shows that the case of equal number of taps after each array elements is the best performance on condition that the total number of tap is fixed.Finally, a high efficient wideband beamformer with only half tap number is proprosed that odd array element is connected with odd delay interval and even array element is connect with even delay interval. Through theory analysis, it is proved that this high efficient structure’s desied signal power and jammer power after interference rejection are the same with Forst space-time structure, the performance difference is caused by the suppression of the noise. Finnally, simulation results verify the correctness of the theory analysis.