Radio age research, manufacturing, communications, broadcasting, television (1941)

The Story of Radar TH/RTEEN YEARS AGO, SCIENTISTS OF RCA LABORATORIES CONDUCTED PIONEER EXPERIMENTS ON THE USE OF RADIO WAVES TO LOCATE SHIPS AND PLANES. By Dr. Irving Wolff RCA Laboratories Princeton, N. J. THE apparatus developed for the detection of objects by means of reflected radio waves has been called radar by the U. S. Navy, and this name has won wide accept- ance. Yet, if the peacetime appli- cations had been given first consid- eration, a name like radio-vision might have been more appropriate. When a scene is photographed or seen by the eye, that scene is il- luminated by artificial light or sun- light and the light reflected or scat- tered from each object is focused on the retina of the eye or on the photo- graphic plate. The only difference between visible light and radio waves resides in the difference in wave length, as is well known. ■Conceivably, therefore, a scene could be illuminated by radio waves from some intense source, and the reflected waves focused on some mosaic structure which would give an indication of the elements on which the radio wave is focused. Such a procedure has actually been proposed but has not proven prac- tical for two reasons. In the first place, the amount of radio power taken to illuminate a large area would be impractically large, and secondly, no known mosaic similar in sensitivity to the photographic plate or the retina of the eye exists for the detection and indication of the presence of the radio signal. If we wish to see a large area on a dark night, we do not attempt to illuminate the whole area all the time. Instead, we concentrate the light into a strong searchlight beam and examine only a small section at a time. By sweeping the search- light beam, we can examine the whole area. In the same way, in order to concentrate radio waves into a beam, we must either have very large radiators or small wave lengths. It is well known, as a matter of fact, that to get a specified beam width, the antenna structure is pro- portional in linear dimension to the wave length. Obviously, an antenna which is too large is inconvenient, if not impossible, as a scanning de- vice. For this reason, microwaves or at least ultra-short radio waves must be used to make a sharp scan- ning beam. By swinging the an- tenna, all parts of the area can be illuminated successively by the radio beam. Object Reflects Signal By attaching an antenna similar to the transmitting antenna to a sensitive radio receiver and swing- ing it so that it points in the same direction as the transmitting an- tenna, an indication is given in the receiver when some object in the path of the radio beam reflects sig- nals back into the receiver. This method of scanning corresponds roughly to the old moving-spot tele- vision scanning system. In similar fashion, by synchronizing the mo- tion of the beam in a cathode-ray tube with the motion of the antenna and modulating the grid with the intensity of the signal, a picture scanned by radio waves rather than light waves can be made visible to the eye. This is one form of radio vision. How Picture Data is Obtained Data used to obtain this picture are obtained entirely by directional information and the intensity of the reflection of the radio signals. Sim- ilarly, it is only this information which is available to the photo- graphic plate or the eye. The dis- tance information is obtained in- directly by interpretation of the sharpness of definition of the images and by binocular vision. If radar had consisted only of apparatus for furnishing a picture as described above, it still would have been useful since the picture could have been obtained through fog and clouds which light will not penetrate. However, radar has made one very important additional contribu- tion which the eye or photographic plate cannot supply, even under per- fect visibility conditions. By means of radio waves and radio techniques, a direct, highly accurate measure- ment of the distance to each of the RCA MICROWAVE EQUIPMENT USED IN 1934 FOR REFLECTION TESTS CONDUCTED IN COOPBHJATION WITH THE U. S. SIGNAL CORPS. THE TRIPOD AT THE RIGHT IS A LONGER-WAVE UNIT DESIGNED BY THE SIGNAL CORPS LABORATORY. [10 RADIO AGE]