This section on terrestrial microwave communications begins by considering free‐space propagation and the effects of terrain, atmosphere, and precipitation on propagation. Multipath fading due to ground reflection or atmospheric refraction is described with a statistical model. Diversity and adaptive equalization are shown to mitigate the effects of multipath fading on digital radio performance. Frequency allocations and planning are discussed, including the effects of interference. Components of a digital radio system are detailed, including the transmitter, receiver, antennas, diversity combiner, and adaptive combiner. Procedures are then described for calculating link performance or determining design parameters.