There are two antennas in a RAIN system.
The first antenna is the one connected to the TAG Chip. This antenna can be of many different shapes, sizes and capabilities.
The second antenna is associated with the reader and again can be of various shapes and sizes. Reader antennas can be horizontally, vertically, or circularly polarized. They can offer steerable beams. They can be fairly large, in a hard case and mounted near a doorway, or can be very thin to allow their incorporation into a shelving system.