  Communications system with analog or hybrid analog/digital architectures
usually relies on a pre-defined codebook to perform beamforming. With the
increase in the size of the antenna array, the characteristics of the spherical
wavefront in the near-field situation are not negligible. Therefore, it is
necessary to design a codebook that is adaptive to near-field scenarios. In
this letter, we investigate the hierarchical codebook design method in the
near-field situation. We develop a steering beam gain calculation method and
design the lower-layer codebook to satisfy the coverage of the Fresnel region.
For the upper-layer codebook, we propose beam rotation and beam relocation
methods to place an arbitrary beam pattern at target locations. The simulation
results show the superiority of the proposed near-field hierarchical codebook
design.
