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 Figure 3-24.—Simple electric fields.

Figure 3-25.—Magnetic field on a single wire.

the H lines take opposite directions between adjacent turns, the field between the turns is canceled. Inside and outside the coil, Where the direction of each H field is the same, the fields join and form continuous H lines around the entire coil. A similar action takes place in a waveguide.

Figure 3-26.—Magnetic field on a coil.

BOUNDARY CONDITIONS IN A WAVEGUIDE

The travel of energy down a waveguide is similar, but not identical, to the travel of electromagnetic waves in free space. The difference is that the energy in a waveguide is conﬁned to the physical limits of the guide. Two conditions, known as BOUNDARY CONDITIONS, must be satisfied for energy to travel through a waveguide.

The first boundary condition (illustrated in ﬁg. 3-27, view A can be stated as follows:

"For an electric field to exist at the surface of a conductor, it must be perpendicular to the conductor."

Figure 3-27.—E field boundary condition.

The opposite of this boundary condition, shown in view B, is also true. An electric field CANNOT exist parallel to a perfect conductor.

The second boundary condition, which is illustrated in figure 3-28, can be stated as follows:

"For a varying magnetic field to exist, it must form closed loops in parallel with the conductors and be perpendicular to the electric field."

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