Figure 71.
Radiation patterns of harmonic antennas.
8.
Nonresonant Antennas.
An antenna has traveling waves that move up and down the
antenna. If we terminate one end of the antenna with a resistance,
while feeding the other, the waves can travel in one direction only.
This is called a nonresonant antenna.
The radiation is in the
direction of the resistance.
This type of antenna radiates
efficiently over a wide range of frequencies.
9.
Half-Rombic Antenna.
a. A half-rombic antenna is similar to an inverted V in shape.
It radiates in a vertical direction.
In figure 72, you see a
comparison of two different half-rombics - one terminated, the other
not. You can see that the advantage of the terminated half-rombic is
that its radiation pattern is in one direction only. The lobes that
are missing in B have combined with the remaining lobes.
The
terminating resistor is 500 ohms with a power rating of one-half the
transmitter's RF output.
92
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