The amplitude Weighting and Σ-Δ beam forming of one dimensional phased array antenna are studied. The effects of amplitude-phase unbalance on angel estimation characteristic are analyzed. A digital method of angle error extraction is provided. The simulation results show that the amplitude unbalance of RF results in the angle extraction sensitivity declined and axis offset, the phase unbalance of RF causes large axis offset, the amplitude unbalance of IF results in the sensitivity of angel estimation deteriorated, and the phase unbalance of IF has little effects on angle estimation.