The present disclosure relates to a phase shifter, an antenna, and a radio communications device. One example phase shifter includes a cavity, a rotating shaft, a main printed circuit board (PCB), a first slidable part, and a second slidable part. The first slidable part is located on a front side of the main PCB and coupled to the main PCB. The second slidable part is located on a rear side of the main PCB and coupled to the main PCB. The rotating shaft is inserted into the cavity and connected to the first slidable part and the second slidable part. The first arc-shaped phase delay line and the second arc-shaped phase delay line are distributed on a circle with a center that is the same as a center of the rotating shaft, and are located on an outer side of a primary central coupling section.