Wideband Digital Array Real-time Delay Technology

In order to obtain more subtle information and meet the identification or precise positioning needs of the target, radar often using the wideband signal which has a high range resolution. When a fully digitized array antenna with wideband signal being transmitted and received do use digital beamforming(DBF) technology, it is called Wideband Digital Array Radar (WDAR). Recently, WDAR is concerned more and more by researchers and becomes hot. However, the wideband of radar signal brings a lot of technical obstacles and one obstacle is the original point of the scanning beam will produce unforgiving drift if the wideband digital radar still uses the traditional narrow-band beamforming technology. This paper analyzes and researchs the cause of the obstacle problem.Firstly, the dissertation give a brief introduction about wideband DBF in frequency-domain and time-domain based on the influences of wideband signal and then presents a method of wideband digital beamforming which is making the outputs of each array element implement delay processing by digital delay lines to accomplish the integer part of the time delay and then the remaining fractional part is compensated by fractional delay filters.Secondly, the designs and implementations of fractional delay filter about finite impulse response (FIR) and all-pass are researched and analyzed, including performance, complexity and stability. The orders of the all-pass fractional delay filter is less than the FIR fractional delay filter, but the stability is bad. in practice, we will first select the Lagrange interpolator and Maximally Flat Group Delay Design , because the two methods give an excellent approximation at low frequencies with low-order and have easy explicit formulas for the coefficients that is quite suitable for real-time coefficient update , however, the approximation bandwidth grows very slowly when the filter order in increased. Least Squares FIR Approximation of fractional delay filter has greater flexibility for bandwidth choice, but only at the expense of numerical problems.On this basis, FIR Variable Fractional Delay(VFD) Filters and all-pass VFD filters is introduced, the results of the simulation are presented and described. Thirdly, the design of FD filter is used to realize wideband digital beamforming and some simulations result shows that the proposed method effectively improve the beam pointing and advance the performance of beamforming.Finally, the software simulations of wideband beamforming based on ADSP21161 is given in the VisualDSP++ environment which practiced two representative algorithms of fractional delay filter, the results show that the procedures be able to achieve beamforming performance.