This book presents the modeling and transmission theory of RF OAM communications. The book features the UCA-based RF point-to-point OAM communication system, the UCA-based RF point-to-multipoint OAM wireless backhaul network, the HCCL structure for long-distance OAM transmissions, and the UCA-based joint OAM RadCom scheme. For the UCA-based RF point-to-point OAM communication system, a 2-D ESPRIT-based distance and AoA estimation method is first introduced, followed by an OAM reception scheme including the hybrid mechanical and electronic beam steering with the estimated AoA and the amplitude...