WAVEGUIDE AS A COMMUNICATION MEDIUM 1253 



these same wires the losses were reduced to 5 to 8 jxt cciil nhox-c llie de 

 values and, by electropolishiug, ('()j)])er wires were l)i()u<i;lit wiiliin '2 i)er 

 cent of the theoretical value. 



An investigation of the effects of aging on the 0,()()() inc conduct i\ity 

 of copper surfaces was conducted jointly by Dawson, Tyn-ell and Heck, 

 using wires which were measured in the coaxial cavity.'' They found (1) 

 that the conductivity of untreated surfaces remained essentially sta- 

 tionary when stored indoors; (2) that the conductivity of hare electro- 

 polished surfaces deteriorated (over a period of months) to a \alue com- 

 paral)le to that for commercially drawn wire; and (3) that a tight bonding 

 coating very greatly slows down the aging process. 



Recent measurements made in the vicinity of 50,000 mc on a sanijjle 

 of commercially-drawn fine-silver waveguide ha\'e indicated that surface 

 roughnesf; effects increased the loss values by appro.ximatcly 20 per cent. 



The overall conclusion would appear to be that it is now feasil)le 

 commercially to produce waveguide surfaces which have excess losses 

 due to surtace roughness no greater than 20 per cent even at frc(iuencies 

 near 50,000 mc, and that by refining the maiuifacturing method it may 

 be possil)le to approach the ideal \'alue more closely. In order to a\'(jid 

 aging effects, a tight-bonding coating and a protective atmosphere may 

 be desirable. 



CIRCULAR ELECTRIC WAVE AND MILLIMETER WAVE TECHNIQUES 



A whole new line of components and techni(iues are recjuired to carry 

 out in the millimeter wave region the same functions that have always 

 been recjuired in a system application, i.e., power generation, amplifica- 

 tion, freijuency-band separation, hybrid division, amplitude and i)hase 

 eciualization, and so forth. With a view to ultimate use in a waveguide 

 transmission system, basic research has been done on all of these ele- 

 ments over a period of years at these Laboratories. 



The importance of primary oscillators and amplifiers to millimeter- 

 wave systems is self-e\'id(Mit, and work has begun going forward in this 

 difficult field under the direction of J. R. Pierce. The results have been 

 published during the last several years. Pierce made the first 6 mm 

 reflex klystron oscillator. ^^ The first 6-mm amplifier, made by John 

 Little,^'' was a travelling wave tube using a conventional helix and it 

 provided 3 db gain. Later, S. Millman^^ introduced the space-harmonic 

 type of travelling-wave amplifier and built several which had over 20 db 

 gain near mm. R. Komi)fner'' devised the backward-wave ty])c of 

 travelling-wave oscillator and built a tube which oscillated from about 

 5 mm to 8 mm. A. Karp^^ devised a simple structur(> for backward-wave 



