| Wideband array signal processing has been an active research area during the past years for its advantages in several aspects over the narrow band processing. In this dissertation, wideband constant beamwidth beamforming (WCBB) in time domain and its application in wideband high resolution DOA (Direction Of Arrival) estimation have been investigated.The main works are as follows:1. Various wideband beamforming methods are analyzed theoretically and via computer simulations. It is shown that time domain WCBB can retain the wideband signal waves without distortion.2. The time domain WCBB design method based on sub-band decomposition is studied. In designing the complex weights for center frequencies of each sub-band, an optimizing method using semi-definite programming' is proposed. As an example, the time domain low-sidelobe WCBB is designed for a 12-element arc array. Simulation results show the effectiveness of the proposed method.3. An improved algorithm directly designing the FIR (Finite Impulse Response-. FIR) filter fan to realize time domain WCBB is presented. By combining the beamformer structure of a FIR filter fan and digital, delay lines, the order of a FIR filter fan is reduced. In the designing procedure, sidelobe and mainlobe regions are considered separately. By computer simulations, it is shown that the algorithm can give more accurate WCBB designing results with low-order FIR filter fan compared to traditional methods.4. The effects of array mismatch errors on time domain WCBB based on ideal array model is thoroughly studied via computer simulations and water tank experiments. It is shown that the practical beam patterns are severely distorted due to these errors. An efficient method is proposed for designing time domain WCBB to alleviate these effects by measuring the practical array model and applying it in the designing procedure. Measurements from a lake experiment are used to verify its effectiveness for arbitrary arrays.5. Based on multi-beam outputs of a time domain WCBB, a time domain wideband high resolution DOA estimation method that can be used for arbitrary array is proposed. An example shows that the beamformer designed by the proposed methodcan greatly reduce computation complexity and improve the precision of DOA estimation. |
