Steering angle mismatch and distance error severely degrade the performance of adaptive beamformer. This digression is more acute in near-field beamforming due to inconvenience of estimating signal’s accurate location especially the radial distance. As the radial distance of signals vary in near-field which is constant in case of far-field. So robustness of near-field array against these errors is a must. Diagonal loading is the most popular and easeful method to increase the robustness of beamformer. This paper presents three robust techniques such as Fixed Diagonal Loading (FDL), Optimal Diagonal Loading (ODL) and Variable Diagonal Loading (VDL) for near-field narrowband beamformer and compares their performance with the optimal beamformer. From the investigation it’s observed that the proposed robust techniques show superior performance than conventional with high directivity in the desired signal direction, low side lobe level and sharp interference and false signal rejection capability.

Keywords : (Beamforming, Near-field, Antenna-array, MVDR, FDL, ODL, VDL)