HF / VHF / UHF (3 MHz – 1 GHz)
Long wavelengths, long range, terrible resolution. Used for over-the-horizon radar that bounces off the ionosphere and for early warning. Can detect stealth aircraft because their RCS reduction breaks down at low frequency.
L-band (1–2 GHz)
Long-range air-traffic-control radar. 200 NM range, modest weather penetration, antennas roughly 10 m wide. Civilian en-route radar lives here.
S-band (2–4 GHz)
Weather radar (NEXRAD), terminal-area ATC, naval surface search. Good balance of range and weather visibility.
C-band (4–8 GHz)
Maritime, weather, satellite uplink. Many ship radars and the older NEXRAD predecessors.
X-band (8–12 GHz)
Most fighter radars, missile seekers, marine navigation, police speed guns. Sweet spot for compact high-resolution systems.
Ku / K / Ka (12–40 GHz)
Automotive cruise-control radar (Ka at 77 GHz), airport surface detection, high-resolution mapping. Heavily attenuated by rain — short range only.
W-band and above (75 GHz+)
Self-driving car sensors, missile seekers, imaging radar. Wavelength is millimetres — you can resolve a human-sized target at 100 m.