U.S. Marine Corps Antenna Mcrp 6 22D Operating Instructions

Antenna Handbook ______________________________ 
2-5
 . 
Figure 2-2. Radiation Patterns.OMNIDIRECTIONAL
BIDIRECTIONAL
UNIDIRECTIONAL 

2-6 _____________________________________ 
MCRP 6-22D
POLARIZATION 
A radiated wave’s polarization is determined by the direction of the
lines of force making up the electric field. If the lines of electric
force are at right angles to the Earth’s surface, the wave is vertically
polarized (fig. 2-3). If the lines of electric force are parallel to the
Earth’s surface, the wave is horizontally polarized (fig. 2-4). When
a single-wire antenna extracts (receives) energy from a passingEARTHSIGNAL...

Antenna Handbook ______________________________ 
2-7
radio wave, maximum pickup results if the antenna is oriented in
the same direction as the electric field component. A vertical
antenna receives vertically polarized waves, and a horizontal
antenna receives horizontally polarized waves. If the field rotates as
the waves  travel through space, both horizontal and vertical com-
ponents of the field exist, and the wave is elliptically polarized.
.
Figure 2-4. Horizontal Polarization.EARTHSIGNAL...

2-8 _____________________________________ 
MCRP 6-22D
Polarization Requirements for Various Frequencies
At medium and low frequencies, ground wave transmission is used
extensively, and it is necessary to use vertical polarization. Vertical
lines of force are perpendicular to the ground, and the radio wave
can travel a considerable distance along the ground surface with a
minimum amount of loss. Because the Earth acts as a relatively
good conductor at low frequencies, horizontal lines of electric force...

Antenna Handbook ______________________________ 
2-9
Advantages of Vertical Polarization
Simple vertical half-wave and quarter-wave antennas provide
omnidirectional communications. This is desirable in communicat-
ing with a moving vehicle. The disadvantage is that it radiates
equally to the enemy and friendly forces. 
When antenna heights are limited to 3.05 meters (10 feet) or less
over land, as in a vehicular installation, vertical polarization pro-
vides a stronger received signal at frequencies up...

2-10 ____________________________________ 
MCRP 6-22D
strength. An example is the picture flutter in a television set when
an aircraft interferes with the transmission path. This factor is
important in areas where aircraft traffic is heavy. 
When vertical polarization is used, less interference is produced or
picked up from strong VHF and UHF transmissions (TV and FM
broadcasts) because they use horizontal polarization. This factor is
important when an antenna must be located in an urban area that
has TV...

Antenna Handbook ____________________________ 
2-11
impossible. However, reception of a desired signal can be improved
by using directional antennas. 
Horizontal half-wave antennas accept radio signals from all direc-
tions. The strongest reception is received in a line perpendicular to
the antenna (i.e., broadside, and the weakest reception is received
from the direction of the ends of the antenna). Interfering signals
can be eliminated or reduced by changing the antenna installation
so that either end...

2-12 ____________________________________ 
MCRP 6-22D
frequency). If a resonant antenna is used for a radio circuit, a sepa-
rate antenna must be built for each frequency to be used on the
radio circuit. A nonresonant antenna, on the  other hand, will effec-
tively radiate a broad range of frequencies with less efficiency. Res-
onant and nonresonant antennas are commonly used on tactical
circuits. Resonance can be achieved in two ways: physically match-
ing the length of the antenna to the wave and...

Antenna Handbook ____________________________ 
2-13
If an antenna is located within a congested urban environment or
within a building, there are many objects which will scatter or re-
raditate the energy in a manner that can be detrimental to reception.
For example, the electric wiring inside a building can strongly re-
radiate RF energy. If a receiving antenna is in close proximity to
wires, it is possible for the reflected energy to cancel the energy
received directly from the desired signal path....

2-14 ____________________________________ 
MCRP 6-22D
IMPEDANCE
Impedance is the relationship between voltage and current at any
point in an alternating current circuit. The impedance of an antenna
is equal to the ratio of the voltage to the current at the point on the
antenna where the feed is connected (feed point). If the feed point is
located at a point of maximum current, the antenna impedance is 20
to 100 ohms. If the feed point is moved to a maximum voltage
point, the impedance is as much as 500...