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Energy Propagation in Waveguides | Up
Neets Module 11-Microwave Principles | Next
Energy Propagation in Waveguides - Continued |
1-11
The two-wire transmission line, illustrated in figure 1-11B, has an instantaneous standing wave of
voltage applied to it by the generator. The line is short-circuited at one-wavelength, at the positive and
negative voltage peaks, but the arrows, representing each field, point in opposite directions. The voltage
across the line varies sinusoidally. Therefore, the density of the E-lines varies sinusoidally.
The development of the E field in a waveguide can be illustrated by a two-wire transmission line
separated by several, double quarter-wave sections, called half-wave frames, as illustrated in figure 1-12.
As shown, the voltage across the two-wire line varies in a sine-wave pattern and the density of the E field
also varies in a sine-wave pattern. The half-wave frames located at high-voltage points (1) and (3) have a
strong E field. The frames at the zero-voltage points (2) have no E fields present. Frame (4) has a weak E
field and is located at a point between maximum and minimum voltage. This illustration is a buildup to
the three-dimensional aspect of the full E field in a waveguide.
Figure 1-12.—E fields on a two-wire line with half-wave frames.
Figure 1-13, view (A), shows the E-field pattern created by a voltage sine wave applied to a
one-wavelength section of waveguide shorted at one end. The electric fields are represented by the arrows
shown in views (B) and (C). In the top view of view (A), the tip of each arrow is represented by a dot and
the tail of each arrow is represented by an X. The E field varies in density at the same sine-wave rate as
the applied voltage. This illustration represents the instant that the applied voltage wave is at its peak. At
other times, the voltage and the E field in the waveguide vary continuously from zero to the peak value.
Voltage and E-field polarity reverse with every reversal of the input. Note that the end view shown in
view (B) shows the E field is maximum at the center and minimum near the walls of the waveguide. View
(C) shows the arrangement of electromagnetic fields within a three-dimensional waveguide.
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