Null fill
Encyclopedia
Null fill is used in radio
antenna
systems which are located on mountain
s or tall tower
s, to prevent too much of the signal
from overshooting the nearest part of intended coverage area. Phasing is used between antenna elements to take power away from the main lobe
and electrically direct more of it at a more downward angle in the vertical plane
. This requires a phased array
. Changing the relative power supplied to each element also changes the radiation pattern
in this manner, and often both methods are used in combination.
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
systems which are located on mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
s or tall tower
Tower
A tower is a tall structure, usually taller than it is wide, often by a significant margin. Towers are distinguished from masts by their lack of guy-wires....
s, to prevent too much of the signal
Signalling (telecommunications)
In telecommunication, signaling has the following meanings:*the use of signals for controlling communications...
from overshooting the nearest part of intended coverage area. Phasing is used between antenna elements to take power away from the main lobe
Main lobe
The main lobe, or main beam, of an antenna radiation pattern is the lobe containing the maximum power. This is the lobe that exhibits the greatest field strength....
and electrically direct more of it at a more downward angle in the vertical plane
Vertical plane
Vertical plane is used in radio to plot an antenna's relative field strength perpendicular to the ground on a polar graph....
. This requires a phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
. Changing the relative power supplied to each element also changes the radiation pattern
Radiation pattern
In the field of antenna design the term radiation pattern most commonly refers to the directional dependence of the strength of the radio waves from the antenna or other source ....
in this manner, and often both methods are used in combination.