Channel Calibration of Amplitude-Phase Errors of DBF Transmitter Based on Maximum Likelihood Estimation

Smart antenna technology can significantly improve the coverage radius, increase channel capacity, reduce transmitting power as well as overcome multipath effects by adaptive beamforming. The performance of digital beamforming is greatly affected by the amplitude-phase inconsistency among the channels. We propose a method of calibrating amplitude-phase errors of RF channels of DBF transmitting antenna together with its realization architecture. A maximum likelihood estimation method is used to calculate the amplitude-phase calibration coefficients of the channels and a compensation matrix is constructed in the FPGA so as to accomplish the calibration procedure. In order to get rid of the nonlinear operation in the estimation algorithm, adjustment is made and thus improves the dynamic range of the algorithm. Prototype of a 61-channel digital beamforming transmitting antenna system with a calibration loop is developed and experiment is carried out under different error conditions. The result of the experiment demonstrates that the proposed algorithm and its realization architecture is of high performance and very economic.