TC 9-64 _________________________________________________________________________
Figure 4-18. Mobile Antennas
4-84. As stated above, a grounded quarter-wave antenna will resonate at the
ground has high conductivity and acts as an electrical mirror image. This
characteristic provides the missing half of the antenna, as shown in the
bottom part of figure 4-19. In other words, the grounded quarter-wave
antenna acts as if another quarter-wave were actually down in the earth.
Figure 4-19. Grounded Quarter-Wave Antenna Image
Characteristics of Quarter-Wave Antennas
4-85. The grounded end of the quarter-wave antenna has a low input
impedance and has low voltage and high current at the input end, as shown in
figure 4-19. The ungrounded end has a high impedance, which causes high
voltage and low current. The directional characteristics of a grounded quarter-
wave antenna are the same as those of a half-wave antenna in free space.
4-26
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