Abstract: To save space and reduce operational costs of base station antennas, modern mobile communications require multiple antenna arrays to be densely packed together, forming multi-frequency shared-aperture base station antennas. The close arrangement of multiple antennas inevitably leads to strong coupling between antennas, causing impedance mismatch, reduced isolation, and significant deformation of the radiation patterns. Therefore, the decoupling of multi-frequency shared-aperture base station antennas has become a hot topic in the industry and academia in recent years. Early decoupling techniques mainly focused on improving impedance matching and isolation of antennas, with relatively little research on decoupling techniques aimed at preserving radiation patterns. After briefly introducing the current research status of decoupling techniques for preserving radiation patterns of base station antennas, This paper focuses on several novel decoupling methods proposed by our team based on principles including induced current cancellation, coupling field cancellation, and radiation blocking. These techniques not only effectively improve impedance matching and isolation,but, more importantly, also preserve the antenna radiation patterns effectively. Simulation and measurement results validate the principles and designs. Some techniques have been applied in products of 5G base station antennas.