A radio frequency (RF) antenna device (140) applies an RF field to an examination space (116) of a magnetic resonance (MR) imaging system (110). The RF antenna device (140) has a tubular body and is segmented in its longitudinal direction (154). Each segment (162, 164) has at least one activation port. The result is that each mode, corresponding to an activation port, may be controlled individually. Accordingly, the inhomogeneity of the subject of interest in the longitudinal direction of the RF antenna device can directly be addressed. There are different ways to build up a z-segmented RF antenna device.