WAVEGUIDE TRANSMISSIOX 



307 



with Equation 6.1-2 and furthermore the two fields together give rise to 

 component Poynting vectors representing power flow. Each component 

 vector has a magnitude at any point equal to the product of the electric and 

 magnetic intensities there prevaihng and a direction at right angles to the 

 two component forces in accordance with Equation 6.1-3. This is illustrated 

 in Fig. 6.2-1 (d). 



Since the fields reside largely outside the conductors, we conclude that 

 the principal component of power flow is through the space between the 

 wires and not through the wires themselves. If, in the case cited above, 

 there is appreciable resistance in the connecting wires, then we may expect 

 that there will be a small component of energy flowing into the wires to be 

 dissipated as heat. To account for this, we may picture lines of electric force 



Circle enclosing 



one half 

 transmitted power 



Dissipotive Material 



(a) (b) 



Fig. 6.2-2. Fields of electric and magnetic force and also direction of power flow in the 



vicinity of conductors, (a) Magnified view showing power tiow along a single 



dissipative wire, (h) Cross-sectional view of parallel-wire line. 



which in the immediate vicinity of the conducting wire lag somewhat behind 

 the portions more remote. This is illustrated by Fig. 6.2-2(a) which shows a 

 highly idealized and greatly enlarged section of the field in the immediate 

 vicinity of one of the two dissipative conductors. The very small component 

 of power flowing into the conductor is designated as the vector P' to dis- 

 tinguish it from the much greater ])ower P which we shall assume is being 

 propagated parallel to the conductor.^ 



The magnetic field associated with two cylindrical conductors consists of 

 circles with centers on the line joining the two conductors, whereas the 

 electric field consists of another series of circles orthogonally related to the 



^ For all metals from which conducting lines are ordinarilj- made, the component of 

 power flowing into the conductor is extremely small compared with the power flowing 

 parallel to its surface. In Fig. 6.2-2(a) therefore, we should regard vector P' as greatly 

 exaggerated in magnitude relative to that of vector F, 



