Radar used to be an acronym for “Radio Detection and Ranging,” but now has entered the language as a real word, and therefore has lost its capitalization.

Radar works by shooting either radio waves or microwaves at an object. A small part of the energy from the wave is reflected back to the antenna. The amount of time it takes for the wave to return allows a calculation to be made to determine the object’s distance.

In the nifty little graphic, the green line is the original wave. The object, which is round, bounces a small portion of the original wave back to the antenna. The returning energy is the blue line.

Based on how long it takes for the blue line to return, the radar’s computer can calculate how far away the blue ball is.

If the blue ball were moving, the radar could find out how fast it is moving by taking several measurements in a row and then calculating the rate of change in the distance over time. Because distance equals rate times time of course.

The same basic principle applies to radar used for weather detection, speed detection (boo!) and ship or airplane detection.

The use of radar for weather detection was actually discovered by accident during WWII. Radar operators noticed that they were getting a lot of interference to their signals when there was rain or snow in the air.

After the war, the scientists who worked on military radar focused on how to interpret this interference to detect weather, leading to the use of radar for weather detection.

Stealth Technology
Most of the time, the same radar antenna acts as both the sender and the receiver. As you saw in the graphic above, a round object reflects only a little bit of the energy back to the antenna. However, if, instead of a ball, the target were flat, more energy would bounce back and the returning signal would be more reliable.

Normal airplanes and ships know this, and include intentional flat features to allow radar to reflect reliably. If you are a passenger airliner, it’s important for the Air Traffic Control radars to be able to find you. So there are specially angled parts added to the airplane to facilitate this. Same goes for trade ships. You want the coast guard to be able to locate you when you send your distress signal.

If you are a stealth military vessel, however, being found by radar is not a good thing. That’s why the stealth bomber looks so odd. It was designed specifically not to reflect radio waves.

The Navy’s new LPD warships (the subject of a future post) do not have a single 90 degree angle on deck. Even the rungs on the ladders are angled so as to not reflect waves.

The military also uses special paints and other materials to absorb rather than reflect radio waves.

Source: Science Channel and wiki