Ground-based radars operate in most allocated frequency bands. Unconstrained by size limitations, they can be constructed large enough to provide acceptable high angular resolution while operating at relatively low frequencies. These bands, however, are crowded with communications signals, so their use by radars is restricted to special applications and geographic areas. Where such long ranges are not required and some atmospheric attenuation and noise is tolerable, ground-based radars may be reduced in size by moving up to higher frequencies. Shipborne Applications .
Physical size becomes a limiting factor aboard ships for many applications including radar systems.
While at the same time, the ship's requirement to operate in various types of weather conditions puts a constraint on the upper portions of the radio frequency spectrum that may be used. This limit is eased somewhat where extremely long ranges are not required. Higher frequencies are usually employed when operating against surface targets and targets at low elevation angles, such as sea-skimming missiles. This cancellation is due to a 180 phase reversal occurring when the return is reflected. As the elevation angle increases, this multipath propagation problem decreases.