Energy Propagation in Waveguides

1-13 Figure 1-15.—Magnetic field on a coil. A similar action takes place in a waveguide. In figure 1-16A, a two-wire line with quarter-wave sections is shown. Currents flow in the main line and in the quarter-wave sections. The current direction produces the individual H lines around each conductor as shown. When a large number of sections exist, the fields cancel between the sections, but the directions are the same both inside and outside the waveguide. At half-wave intervals on the main line, current will flow in opposite directions. This produces H-line loops having opposite directions. In figure 1-16A, current at the left end is opposite to the current at the right end. The individual loops on the main line are opposite in direction. All around the framework they join so that the long loop shown in figure 1-16B is formed. Outside the waveguide the individual loops cannot join to form a continuous loop. Thus, no magnetic field exists outside a waveguide. Figure 1-16A.—Magnetic fields on a two-wire line with half-wave frames.