WAVEGUIDE TRANS.\fISSION 299 



the directions and also the relative intensities of lines of electric force in the 

 wave front could be mapped. It is probable that certain of these modes were 

 observed and identitied for the tirst time. 



Shortly afterwards, sources giving wavelengths in air of fifteen centi- 

 meters became available and the experimental work was transferred to air- 

 filled copper pipes only 5 inches in diameter. At this time, a 5-inch hollow- 

 pipe transmission line 875 feet in length was built through which both 

 telegraph and telephone signals were transmitted. Measurements showed 

 that the attenuation was relatively small. This early work, which was done 

 prior to January 1, 1934, was described along with other more advanced work 

 in demonstration-lectures and also in papers published in 1936 and 1937.'' 



It was recognized at an early date that a short waveguide line might, with 

 suitable modification, function as a radiator and also as a reactive element. 

 These properties were likewise investigated experimentally, and numerous 

 useful applications were proposed. Descriptions may be found in the numer- 

 ous patents that followed. These properties were also the subject of several 

 experimental lectures given before the Institute of Radio Engineers and 

 other similar societies by the writer and his associates during the years 1937 

 to 1939.^ Included were demonstrations of the waveguide as a transmission 

 line, the electromagnetic horn as a radiator, and the waveguide cavity as a 

 resonator. An adaptation of the waveguide cavity was used to terminate a 

 waveguide line in its characteristic impedance. 



From the first, progress was very substantial and by the autumn of 1941 

 there were known, both from calculation and experiment, the more important 

 facts about the waveguide. In particular, the reactive nature of discon- 

 tinuities became the subject of considerable study, and impedance matching 

 devices (transformers), microwave filters, and balancers soon followed. Also 

 a wide variety of antennas was devised. Similarly, amplifiers and oscillators 

 as well as the receiving methods followed. 



As might be expected, a great many people have contributed in one way 

 or another to the success of this venture. Particular mention should be 

 made of the very important parts played by the author's colleagues, Messrs. 

 A. E. Bowen and A. P. King, who, during its early and less promising period, 

 contributed much toward transforming rather abstract ideas into practical 

 equipment, much of which found important military uses immediately upon 

 the advent of war. Also of importance were the parts played by the author's 

 colleagues. Dr. S. A. Schelkunoff, J. R. Carson, and Mrs. S. P. Meade, who, 

 in the early days of this work, provided a substantial segment of mathe- 

 matical theory that previously was missing. During the succeeding years, 

 Dr. Schelkunoff, in particular, made invaluable contributions in the form 



■* A description of one of the earlier lectures appears in the Bell Laboratories Record 

 for March 1940. (Vol. XVIII, No. 7, p. 194.) 



