Word: beaming
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Dates: during 1940-1949
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...problem in radar is to generate enough power to get a detectable echo from a distant point. Of the total energy sent out in a radar beam scanning the skies, only a tiny fraction hits the target (e.g., a plane), and a much tinier echo gets back to the receiver. Engineers estimate that if the outgoing energy were represented by the sands of a beach, the returning echo would be just one grain of sand...
...serious shortcomings: 1) they gave only a crude, distorted echo; 2) they had some blind spots, especially close to the ground; 3) they required huge "bedspring" antennae. Microwaves solved all these problems at one stroke. These tiny waves, which are measured in centimeters, can be formed into a beam precise enough to detect the periscope of a submerged submarine...
...oscilloscope" ("scope" for short), radar's screen, which is a cathode-ray tube such as is used in television. The most common type, the "Plan Position Indicator," is a circular dial with an electronic beam like a minute hand, which sweeps around the dial in synchronization with the scanning antenna, painting in its fluorescent wake a picture of what radar sees...
Radar's ability to report what it sees depends on differences in its targets' reflecting power (which engineers call the "dielectric constant"). Metal is an excellent reflector; earth, an indifferent one. Water also is a good reflector, but because of its flat surface, the radar beam caroms off at an angle and no echo reaches the receiver (except from a spot in the center of the beam); hence water appears black on the scope...
Echoes from the earth are affected by the angle at which the radar beam strikes its irregularities, and by "shadows" cast by raised objects. Thus mountain tops and ridges are easily distinguishable from the surrounding terrain...