Study On Digital Beamforming At Subarray Level And Weighting Method

In radar system, it is a basic and of the greatest importance to generate sum and difference beam patterns with low sidelobes. To this purpose, two types of tapering functions are usually adopted: the Taylor for the sum beam and the Bayliss for the difference beam.In this paper, we mainly study on properties of digital beamforming with subarray, construction of weighting network and an analog and digital weighting approach with plane array. It is necessary to reduce the hardware complexity of the system and the computational cost by using subarrays, processing digitally at subarray level in order to obtain satisfying performance.First of all, we present the model of target angular estimation based on maximum likelihood approach under a main beam interference condition, and investigate the yardstick of target estimation performance—CRLB (Cramer Rao Lower Bound), we present the particular process of its derivation, we discuss the realization approach of a double difference beam which can be used to suppress jammers under mainbeam interference condition and form the four-channel monopluse system.We discuss three ranks taper form with arrays, suitable for uniform linear arrays and plane arrays. We present a weighting form which makes the antenna be switched freely between sum and difference modes, we can find the digital taper vector by weighting approximation or pattern approximation criterion, and obtain difference pattern with satisfying sidelobe, we can suppress jammers using adaptive taper based on LCMV (Linear Constraint Minimum Variance) criterion.For plane array, this paper suppresses sidelobes of sum and difference beam patterns using analog and digital weightings. Analog weighting is obtained based on adaptive approach which minimizes the jammers within the whole sidelobe area. The advantage of this taper is that it can suppress sidelobes of sum and difference beam patterns synchronously, while needs not to adopt different taper, therefore, reduces the hardware cost effectively, but the limitation of this method is that the effect of sidelobe suppression is not ideal. Therefore, digital weighting is adopted further at subarray level in order to approximate the effect of conventional taper. The performance of sidelobe is improved largely.In the end of the paper, we analyze mathematical description and properties of digital beamforming with subarrays, perform beam scanning at subarray level. By post-processing the subarray outputs with digital taper network we can obtain approximately identical subarray patterns within mainlobe areas. We discuss three forms of desired subarray patterns respectively, in order to reduce computational cost we introduce corresponding approximately desired subarray patterns, the sidelobe level of patterns scanned at subarray level is reduced to some extent after processing of weighting network. At last, we discuss the optimum weighting for beam scanning at subarray level.We simulate and analyze all the presented algorithms. The simulation results demonstrate the efficiency of the algorithms.