Study On Robust Wideband Interference Suppression Algorithm

With the development of electronic technology,the working environment of radar is becoming complex.How to effectively suppress interference is crucial to enhance the detection ability of radar in such environment.Most of the existing radars work in a narrowband condition,so the interference suppression method usually refers to narrowband interference suppression.When the wideband interference is propagating in space,due to the time difference between the elements,the complex envelope of the signal changes rapidly,which results in the weak correlation among signals by different elements,thus the wideband interference cancellation decline.Therefore,the study of robust wideband interference suppression algorithm is of great significance.This thesis mainly focuses on robustwideband interference suppression algorithm.First of all,the mathematical model of narrowband signals is established.The conventional beamforming(CBF)method,three optimal beamforming techniques and adaptive sidelobe canceller(ASLC)are introduced which lays foundation for the wideband interference cancellation.For the specified elements,they are always designed at a fixed working frequency.When wideband signals impinging upon the received arrays,the dispersion phenomenon occurs.The dispersion phenomenon is largely related to the relative bandwidth of the signal,the size of the array and the angle of signal.Not only the adaptive degree of freedoms have relationship with the number and angle of injection,but also with the relative bandwidth of the interference.The wideband signal has a certain bandwidth that will consume additional adaptive degrees of freedom in the interference cancellation.This thesis mainly focuses on two robust wideband interference suppression algorithms.The first method is to add time delay to the elements to improve the performance.The size of time delay has an important influence on the overall performance of the robust wideband interference algorithm,however,the existing theory has not yet put forward a clear criterion for the determination of the time delay.Based on the maximum cancellation ratio criterion,this thesis proposes a method to select the size of the time delay,and the validity of the method is verified.The second method implements wideband interference suppression through Fast Fourier Transform(FFT).First,the Fast Fourier Transform of the signals received by the elements is performed.Thus,the signal received is converted from the time domain to the frequency domain.The weights are calculated separately at different frequencies and then applied the interference cancellation.The output signal can be recovered by the Inverse Fast Fourier Transform(IFFT)of cancelled frequency domain signal.Last but not least,from the mathematical point of view,this thesis proves the equivalence of the two methods,and explains the difference caused by parameter settings.