Over nearly 50 years, mobile radio-access-network (RAN) base transceiver station (BTS) antenna technology has advanced from single-frequency-band antennas with a single port to antennas with dozens of ports and multiple frequency bands. All of this technology is now contained within a housing roughly the same size as was used back when public mobile communications networks first started in the 1980s.
This evolution of antenna technology has been driven by the need to overcome the vagaries of radio signal propagation, where there can be multiple signal reflections from the ground and other objects in the natural and built environment, as well as direct or refracted paths that can be partially blocked. These multiple signal paths may combine or cancel out each other, producing an unreliable communications channel.