The one-sentence version
A radar transmits a short burst of radio energy, waits for that burst to bounce off something, and measures how long the round trip took. Radio waves travel at the speed of light, so the time delay converts directly into distance. Repeat thousands of times per second while rotating the antenna and you get a live map of everything around you.
Step 1 — the pulse
The transmitter sends a microsecond-long burst of radio waves through a directional antenna. The frequency is usually somewhere between 1 GHz and 100 GHz depending on what the radar is looking for. Lower frequencies travel further and see through weather; higher frequencies give finer detail but get absorbed by rain. Aircraft radars sit around 8–12 GHz (X-band); weather radars around 3–10 GHz (S/C-band); car radars around 77 GHz.
Step 2 — the echo (range from time)
After transmitting, the same antenna switches to listen mode. Anything solid in the beam — a plane, a ship, a raincloud, a bird — reflects a tiny fraction of the energy back. The receiver times how long the round trip took.
range = (speed of light × round-trip time) ÷ 2
Light covers 300 metres in one microsecond, so a target 15 km away returns its echo about 100 microseconds after the pulse was sent. The radar can fire its next pulse and listen again before you finish blinking.
Step 3 — the sweep (bearing from antenna direction)
The antenna rotates (or, in modern systems, electronically steers) and tags every echo with the direction it was pointing when the echo came back. That gives you the second coordinate. Range plus bearing equals position, and a screen full of those is the familiar PPI scope — the green sweep you've seen in every aircraft carrier movie and every browser radar game.
Step 4 (optional) — Doppler for speed
If the target is moving toward or away from the radar, the returned echo's frequency shifts very slightly — the same effect that makes a passing ambulance siren change pitch. Measuring that shift gives the target's velocity along the radar's line of sight. This is how police radar guns, weather radar wind maps, and missile-warning systems work.
Why the display fades
On a real PPI scope the green afterglow is the phosphor itself — the screen literally keeps glowing for a few seconds after the electron beam paints it. Modern digital radars fake this fade in software because operators read a fading trail more easily than a hard-edged dot. The same convention drives the trail behavior in Signal//Lock — newer contacts are bright, older ones decay, and reading that decay is the core skill of the game.
Common questions
- Can radar see through clouds? Yes. That's its main advantage over optical systems. Heavy rain attenuates higher-frequency radars but most weather is transparent to S- and L-band.
- Can radar see stealth aircraft? Sometimes. Stealth shapes scatter X-band energy sideways instead of back toward the receiver, but lower-frequency radars (VHF/UHF) still get returns.
- What does RADAR stand for? Radio Detection And Ranging. The acronym was coined by the US Navy in 1940.
- How is sonar different? Same idea with sound waves in water instead of radio waves in air. Sound is millions of times slower, so sonar updates much less often than radar.