Radar

The U.S. has spent half again as much (nearly $3 billion) on radar as on atomic bombs. As a military threat, either in combination with atomic explosives or as a countermeasure, radar is probably as important as atomic power itself. And while the peacetime potentialities of atomic power are still only a hope, radar already is a vast going concern--a $2 billion-a-year industry, six times as big as the whole prewar radio business.

To fighting men, radar by now is as routine a war tool as a rifle, but it has rewritten the textbooks of warfare. It has also given man a sharp sixth sense which projects him into a world where almost any fantasy seems possible.

The Beam That Sees. An electronic supergadget which "sees" as well in the dark as in the light, radar projects a radio beam which, on striking an object near or far, returns an echo that is translated into a visual image on the radar screen. Radar can see the flight of a shell, the wake of a ship, the explosion of a target, the fall of a hit plane. At sea, it can detect buoys, reefs and other ships more than 20 miles away.

From the air, by night or day or through the thickest cloud, it lays open the terrain below like a relief map, showing coastlines, ships, harbors, jetties, mountains, lakes, rivers, bridges, cities. At close range, with the narrowest radar beam, it is possible to see a city's river fronts, avenues, even buildings.

Normally the screen shows the size but not the exact shape of the detected object. Occasionally it may get an effect of almost photographic sharpness (the screen in Artzybasheff's drawing, though an exaggerated animation, is based on a ''shadow effect" actually caught in one freakish radar picture of a plane a couple of hundred yards away).

Battle Results. Radar's fantastic capabilities have been dramatized again & again in battle. It was radar that enabled a .U.S. warship to smash the battleship Jean Bart at Oran with one salvo from 26 miles away. German radar-directed fire sank the British battle cruiser Hood, and British radar in turn tracked down the Bismarck. It was a radar operator who gave the tragically ignored warning of approaching Japanese planes at Pearl Harbor.

Radar was chiefly responsible for defeating the U-boat and the buzz-bomb. The British say that radar and 300 R.A.F. pilots won the Battle of Britain. It was a vital aid to airmen and paratroopers over Normandy on cloudy Dday, and to the U.S. Navy in sinking the Japanese fleet. Radar opened the roof of Hitler's Europe for the day-&-night, all-weather body punching that crippled the Wehrmacht--and it lifted the Nipponese lid.

For all these uses and countless others, an amazing variety of radars have been developed. There are "early warning" radars which can pick up a plane more than 100 miles away and show how fast and in what direction it is flying; fire-control radars which automatically aim and fire a machine gun or antiaircraft gun more accurately than a human gunner; special radars that provide eyes for night fighter pilots, guide planes to blind landings (called G.C.A., "Ground-Controlled Approach"), observe stratospheric weather balloons and detect storms. Engineers think that it may even be possible some day to develop a missile that will guide itself to a target by radar.

Pioneers & Progress. Like most great inventions, radar had many inventors.

Among those in the U.S. who had a hand in its development were: a Navy quartet. of physicists and radio hams--Albert H. Taylor, Leo C. Young, Robert M. Page and Louis A. Gebhard--who pioneered radar in the '205 and '303; the Signal Corps' Colonel Roger Colton (now an A.A.F. major general), whose laboratory staff at Fort Monmouth designed the first Army set; Stanford University's R. H. and S. F. Varian, who invented the important klystron tube; and a great anonymous army of scientists at M.I.T.'s Radiation Laboratory, Bell Telephone Laboratories, General Electric, many another industrial laboratory. The U.S. also owes much to Rear Admiral Harold G. Bowen, who, as chief of the Naval Research Laboratory, sparked its radar pioneering.

U.S. progress in radar was paralleled by a team of British physicists under Sir Robert A. Watson-Watt. (The British first called it "radiolocation," later accepted the U.S. word "radar."*) There were also the Germans, who were known to be experimenting with radar as early as 1935; the Japs, whose physicist Hide-tsugu Yagi was working on basic shortwave studies long before the war (the U.S. Navy called its early radar antennae "yagis"); the French, who in 1936 installed on the Normandie a crude radar for detecting icebergs.

The one man with the best claim to discovery of radar's principle was the 19th Century German physicist Heinrich Hertz, who in 1887 bounced a hertzian (radio) wave off a zinc plate and caught its echo on a resonant circle of copper wire.

Idea into Miracle. Radar's significant history began one hot summer's day in 1922, when the Navy's Albert Taylor and Leo Young, noticing that ships passing up & down the Potomac distorted short-wave signals they were sending across the river, conceived the idea that radio waves might be useful in detecting enemy warships. By 1940, Army & Navy radio experts had built a few bulky sets which could locate sizable objects on the water or in the air, but could not identify them.

The real miracle of radar was what happened in the next five years: a job of U.S. and British scientific teamwork which created almost overnight a revolutionary instrument, and a vast industry which would normally have taken a generation to develop.

Shouts & Echoes. The basic secret of radar is that short radio waves behave very much like light. In the spectrum of electromagnetic radiation, which ranges from the extremely short cosmic rays (trillionths of an inch) and gamma rays (which are released in an atomic bomb) to extremely long electric power waves (6,000 miles), radio and light waves are almost next-door neighbors, though light waves are much shorter than radio.

Like light, the ultrashort radio waves used in radar can be focused in a beam, are reflected by solid or liquid surfaces, travel with the same speed as light (186,000 miles a second). But for "seeing" distant objects, radio waves have a great advantage over light: they penetrate fog, clouds and smoke, reach out to far greater distances than the naked eye. And unlike light, radio impulses can easily be controlled to give an exact, automatic measurement of the distance to the detected object.

In its simplest terms, a radar set shoots radio energy at a target, catches the reflected echo, times the round trip, divides by two, and. since the speed of the radio wave is known, translates all the information into a "blip" of light on a fluorescent (television) screen showing the target's distance and position.

In practice radar is not that simple. A conventional transmitter, sending continuous radar waves, would not do, for the same reason that a man roaring incessantly at a cliff would get back only a confusing noise. To get a clear, time-able echo, he must utter a short, sharp shout. That is exactly what radar does. It sends staccato "pulses" of electric energy, each less than a millionth of a second in length, at a rate of about 1,000 a second. Each pulse has time to make a round trip (about a thousandth of a second for a target 100 miles away), and record its message without interference from the next.

The big 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.

Little Waves from Overseas. To produce a compact instrument, small enough to be carried in a plane, that would handle the enormous power nee:'ed (surpassing that of the most powerful radio station), required a revolution in radio.

One fine autumn day in 1940, a. British engineer, carrying a small black bag, debarked from a ship in Manhattan. He was met by a Bell Telephone engineer. They meandered into a movie before driving out to the Bell man's suburban house. Next day, satisfied that they had shaken off any possible spies, they turned up at the Bell Laboratories with the supersecret device that broke the radar bottleneck. The Briton, a member of a radar mission to the U.S., brought designs anda model of an electronic tube called the "magnetron."

The magnetron, by whirling electrons at high speed inside a magnetized cylinder, produced extremely short radio waves and great power. Its principle was not new. But the British had developed a high-powered version of it, and U.S. engineers perfected its radar adaptation.

With the magnetron's help, the M.I.T.

Radiation Laboratory and Bell Laboratories proceeded to develop an uncharted part of the radio spectrum--microwaves. For radar, the relatively long radio waves (one and a half meters) used early in the war had 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.

Four-Part Reporter. The major working parts of a typical radar set are:

P:A bowl-shaped antenna which beams the outgoing radio pulses, catches the echo.

P:A high-powered transmitter using a magnetron.

P:A receiver with a "klystron," "lighthouse" or other oscillating tube, used to convert the microwave echo to a lower radio frequency so that it can be amplified.

P:An "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.

One of radar's toughest identification problems--and one of the most fascinating sidelights on the great supergadget--was how to tell whether detected planes or ships were friendly or hostile. It was solved by an ingenious instrument called I.F.F. ("Identification, Friend or Foe"). When an I.F.F.-equipped plane is hit by a friendly radar beam, the instrument automatically flashes back a coded identifying signal.

Privacy in the Bathtub. Radar still has many limitations. Since it travels only in a straight line, it cannot "see" beyond the horizon. Because it cannot see through water or most solid obstructions, there is little chance that it will ever invade the privacy of four walls.

At ground level, a radar beam is scattered by ground irregularities. For this reason, contrary to Sunday-supplement predictions, it is not practical as an anticollision device on autos or railroads.

Many of radar's wartime jobs, based on locating a noncooperating target, in peacetime could be performed just as well by ordinary radio. Nonetheless, engineers predict a great postwar future for it. For one thing, they expect it to be required equipment on ships and possibly on commercial planes.

On a ship, radar is insurance against collision with icebergs, rocks or other ships; it can take a vessel at full speed through a crowded harbor and dock it in the foggiest weather. In the air, radar, supplemented by a map of the terrain, would keep a pilot as well oriented as if he were flying over his living-room rug, would ward off collisions with mountains and other planes. It would, of course, prevent such accidents as the Army bomber's crash into the Empire State Building last month.

Phenomenon in a Pipe. Radar enthusiasts have suggested many other uses, from controlling traffic at airports to studying the speed of high-flying birds. But to physicists, radar is only an item in the vast possibilities opened by the discovery of microwaves.

Microwaves are still a largely mysterious phenomenon. They flow through a pipe like water, are reflected by the human body, can be "modulated" to carry sound or pictures. Thus microwaves make it possible to point a beam at someone miles away and talk to him privately, or to broadcast television or movies via relay towers or relaying planes (see RADIO).

Most exciting of all to academic scientists is radar's miraculous precision in measuring time. Men can now count time in millionths of a second, and scientists are sure that important new discoveries about man's universe--from atoms to stars--will follow. Some of them already dream of bouncing a radar echo off the moon.

-The man who coined the word "radar" (for Radio Detection and Ranging) was, according to the Navy, Commander (now Captain) S. M. Tucker.

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