312 BELL SYSTEM TECHNICAL JOURNAL 



Section III. First, however, in the general discussion which immedi- 

 ately follows and, in particular, in the comparison with the usual guided 

 wave transmission systems, attention will be confined to the ideal 

 non-dissipative structure. This simplification brings out, in a simpler 

 and more striking way, the peculiar transmission characteristics of the 

 system, while, at the very high frequencies involved, it introduces 

 negligible error except as regards the attenuation due to dissipation. 



In the ordinary type of guided-wave systems, such for example, as 

 that composed of two concentric conductors, or two parallel wires, the 

 guiding conductors form two sides of a circuit in which equal and 

 opposite currents flow, and the transverse lines of electric intensity 

 terminate on the two sides of the circuit. In the system under con- 

 sideration there is only one conductor and consequently there is no 

 circuit in the usual sense. Corresponding to this difference in physical 

 structure there are striking differences in the character of the waves 

 propagated. 



In the first place, in the ordinary type of guided wave system, the 

 wave employed for the transmission of power and intelligence is the 

 Principal Plane Wave. For the ideal non-dissipative case, the field of 

 this wave is entirely transverse to the axis of the system; that is, the 

 axial components of the electric and magnetic intensities are every- 

 where zero. Furthermore all frequencies are transmitted without 

 attenuation with the same phase velocity; that of light in the medium. 

 (Of course dissipation modifies the phenomena somewhat but in actual 

 systems designed for efficient transmission the Principal Wave ap- 

 proximates to that just described.) 



In the hollow conducting cylinder, on the other hand, no principal 

 transverse wave can exist; that is, there must exist inside the cylinder 

 either an axial component of the electric or the magnetic intensity, or 

 both. Physically this is answerable to the absence of a circuit on 

 which the transverse lines of force might terminate. Thus in the 

 hollow conducting cylinder all the possible waves must be complemen- 

 tary waves; ^ a type which is ignored in the ordinary transmission 

 system. 



A second outstanding distinction is that in the hollow conducting 

 cylinder, all frequencies below a critical frequency are attenuated while 

 frequencies above the critical frequency are freely transmitted without 

 attenuation.^ In this respect the system behaves like a Campbell high- 



^ See "Guided and Radiated Energy in Wire Transmission," John R. Carson, 

 Jour. A.I.E.E., October 1924. 



* It will be understood, of course, that this is strictly true only in the ideal case of 

 no dissipation. 



