_______________________________________________________________________ Antennas
Methods of Feeding Energy to an Antenna
4-81. Voltage and current distribution for the half-wave antenna (shown in
figure 4-17) is the same as that for the antenna discussed earlier in this
chapter. A point closely related to the voltage and current distribution on an
antenna is the method of feeding the transmitter output to the antenna. The
simplest method of feeding energy to the half-wave antenna is to connect one
end through a capacitor to the final output stage of the transmitter. This
method is often called the end-feed or voltage-feed method. In this method
the antenna is fed at a point of high voltage (the end).
Figure 4-17. Standing Waves of Current and Voltage
4-82. Energy may also be fed to the half-wave antenna by dividing the
antenna at its center and connecting the transmission line from the final
transmitter output stage to the two center ends of the halved antenna.
Because the antenna is now being fed at the center (a point of low voltage
and high current), this type of feed is known as the center-feed or current-
feed method. The point of feed is important in determining the type of
transmission line to be used.
QUARTER-WAVE ANTENNAS
4-83. As you have studied in the previous sections, a one-half wavelength
antenna is the shortest antenna that can be used in free space. If we cut a
half-wave antenna in half and then ground one end, we will have a grounded
quarter-wave or Marconi antenna. This antenna will resonate at the same
widely used in the military. Most mobile transmitting and receiving antennas
(illustrated in figure 4-18) are quarter-wave antennas.
4-25
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