The Early History of Radar' 



By R. M. Page 



Director of Research, 

 U.S. Naval Research Laboratory, Washington, D.C. 



[With 4 plates] 



Technological innovation grows out of contemporary technology, 

 which in turn rests on the research and scientific discoveries of an 

 earlier day. Only when clear distinction is made between innovation, 

 contemporary tecluiology, and contemporary scientific knowledge can 

 lines of interdependence be meaningfully drawn. 



The combination of live basic ideas constitutes the innovation 

 which is radar. They are (1) that electromagnetic radiation at high 

 radio frequency be used to detect and locate remote reflecting objects, 

 (2) that the radiation be sent out in pulses of a few microseconds dura- 

 tion, separated by "silent" intervals very many times the pulse dura- 

 tion, (3) that pulses returned from reflecting objects be detected and 

 displayed by receiving equipment located at the point of transmission, 



(4) that distance be determined by measuring in terms of an independ- 

 ent time standard the time of flight of pulses to "target" and back, and 



(5) that direction be determined by use of highly directive radio 

 antennas. 



We first identify the scientific knowledge underlying these ideas. 

 Faraday and Maxwell had established the theoretical possibility of 

 the electromagnetic field. Hughs had demonstrated its existence at 

 radio frequency. Hertz had demonstrated that radio waves behaved 

 as light waves, obeying the Ivnown laws of propagation and reflection. 

 Appleton and Barnet had demonstrated that radio waves could be 

 used in interferometer fashion to determine apparent height of the 

 ionsphere. Their method used phase velocity to measure the differ- 

 ence in length of two propagation paths. Swann and Frayne had sug- 

 gested and Breit, Tuve, and Taylor had demonstrated that radio waves 

 could be used to measure ionosphere height by observing the relative 

 flight time of pulses of radio transmission. Their method used group 



1 Reprinted by permission from Proceedings of the Institute of Radio Engineers, vol. 50, 

 No. 5, May 1962. 



315 



