Broadband Constant Beamwidth Beamforming Method

Broadband signal processing has become an important research topic, because of the fact that broadband signal has many merits, such as carrying large amount of information, weak reverberation background correlation, good performance of target detection, parameter estimation and feature extraction of a target. In this dissertation, we focus on the problem of broadband array signal processing, some important aspects of broadband array signal processing are discussed in detail, including the narrowband beamforming optimization, the broadband constant beamwidth beamforming optimization in both time domain and frequency domain. The main research are summarized as follows:1. Studied the common narrow beamforming algorithms and analysed each algorithm's performance such as robustness, convergence. Conclude that we can use different algorithms according to the input SNR. Against arbitrary structure and the nature of the array element, studied the adaptive beamforming optimum design method.2. Systematicly analysed the structure and characteristics of a variety of broadband beamforming method, and utilized simulation result to illustrate that when the signal impinged from the non-beam pointing direction within mainlobe region, the time domain output signal of classic time domain broadband beamforming exists distortion. Researched FIR (Finite Impulse Response: FIR) digital filter design theory based on the second-order cone programming, and simulated a precise delay FIR filter.3. Detailedly discussed the frequency domain constant beamwidth beamforming design method. Researched and analysed broadband frequency domain constant beamwidth beamforming of linear array and arbitrary structure array, simulated and verified correctness of the methods.4. In-depth studied the time domain constant beamwidth beamforming design method based on frequency subband division. The method firstly designed constant beamwidth weighted on the center frequency of each subband via second-order cone programming, then used FIR filter to fit the constant beamwidth weighted on these frequencies to achieve time domain constant beamwidth beamforming.5. Studied the methods of directly designing FIR filters to achieve time domain constant beamwidth beamforming. Took designing broadband constant beamwidth beamforming of a uniform discrete circular array for example, used two types of optimization methods for simulation, and compared the simulation results. Simulation results show that using the second type of method, which would require best approximation the expectations beam in the mainlobe region while less than a given value in the sidelobe region, the beam can be better meet the design requirements.