An approach to direction-of-arrival (DOA) estimation for multiple broadband farfield signals is proposed. The approach uses a beamspace preprocessing structure based on frequency domain frequency-invariant beamforming. The frequency-invariant beamformers are designed using the optimal array pattern synthesis technique based on second-order cone programming (SOCP). The proposed method only ensure that the beam patterns are constant within the main beam region while control the sidelobes, which leads to smaller focusing error. Numerical results show that the proposed method provides lower resolution threshold and lower root-mean-square error (RMSE) of estimate compared with the existing method.