A base station antenna includes a panel that has a ground plane, first and second arrays that have respective first and second sets of linearly arranged radiating elements mounted on the panel, and a decoupling unit positioned between a first radiating element of the first array and a first radiating element of the second array. The decoupling unit includes at least a first sidewall that faces the first radiating element of the first array, a second sidewall that faces the first radiating element of the second array and an internal cavity that is defined in the region between the sidewalls. The first and second sidewalls are electrically conductive and electrically connected to the ground plane.