Marine radar.

Most marine radars operate in the 10 GHz (3 cm wavelength) and 3 GHz (10 cm wavelength) frequency bands. Although a bit outdated, these bands are still referred to as X band (10GHz) and S band (3 GHz). Radars operating in the 10 GHz band (3 cm wavelength) provide much better definition (more detailed picture) than the radars operating in the 3 GHz band (10 cm wavelength), ie they are more likely to pick up very small objects and the radar traces of land are better defined.

The radars operating in the 3 GHz band usually provide greater range coverage. The latter are usually used for early detection of objects at ranges greater than 20 nautical miles, whilst the former is used to provide more detailed coverage at ranges below 20 nautical miles.