An annular rotary RF coupler for installation about a vertical support structure, such as the mast of a ship. Two annuli are divided into circumferential increments providing a cellular structure of individual waveguide cross-sections. A lower annulus (stator) remains fixed, the individual waveguide sections therein being fed from a power-divided, equal-phase, feed configuration. The oppositely facing upper annulus (rotor) rotates with respect to the lower one about the common mechanical center of rotation of a mechanically rotating antenna system. Connection to the rotating waveguide sections may be through power combiner/divider means, or individual subarrays may be discretely connected to one or more waveguide sections in the rotating annulus. For power tapering across an antenna array aperture, the waveguide section dimensions in the circumferential direction within the rotating annulus are appropriately tailored. A single enlarged stator cell is employed to accept the residual energy in the power distribution transmission line, eliminating the need for a termination load and the corresponding power loss.