Think of the wireless radiation pattern as a fat donut with the antenna sticking through the middle of the donut. As the gain of the antenna is increased the fat donut starts to flatten out significantly to the point where you will have a donut so flat it will resemble a CD disk: Round but very flat and anything above it or below its path won't see it.
At right: Radiation pattern of the 2dB omnidirectional antenna at right (bottom pattern in image)
A low gain (2dB) omnidirectional antenna like this provides a strong signal in every direction
Intended for short range meshed networks and reaches everyone within its range.
If you are in a building and need to cover the rooms around you then you are better off with a 2dbi dipole antenna, as they make sure you cover everyone equally in all directions
Diagram below shows the radiation pattern of a 2dBi omni-directional dipole antenna (vertically polarized):
This diagram shows the relationship between the E and H planes for a vertically polarized omni-directional dipole antenna. This is the type used in wireless repeater systems and it is intended for short range meshed networks and reaches everyone within its range.
Polarization of the wireless antenna is the orientation of the wireless signal. It can be vertical, horizontal, circular or combinations of these.
The E-plane and H-plane are reference planes for linearly polarized antenna.
|Radio waves do not penetrate obstacles very well.
High-gain antennas have a flat radiation pattern: So, a larger antenna will only help for long range; it will not help if you have differing elevations. Use high power antennas to send a signal long distances to a very specific and focused point. The higher the gain, flatter the signal radiation pattern.Low power antennas send their signals to higher and lower elevations in local area: Everywhere within their 100-200 foot range.
Gain of an antenna is a measure of its enhancement of signal strength: Gain is measured by the dBi rating.
Calculating Gain from addition of an antenna:
Antennas generally have greater coverage at the expense of range, and greater range at the expense of width of coverage area ("half-power beam width"). Therefore, omni-directional antennas, which radiate the beam in all directions (on a horizontal plane) generally have gains no higher than 12dBi, while directional antennas can have gains up to 30dBi. As a general rule of thumb: The higher the gain, the narrower the beam width (coverage area). Half-power beam width is the specification of the antenna's coverage area. It is measured relative to the points at which the antenna's radiation drops to half its peak value.
INDOORS / BUILDINGS See also this page on dipole antennas.
Metal reflects the signal. Modern houses may also have foil backed plasterboard to meet fire regulations and modern glass has a metal content.
This said, as a general rule 802.11g/ WiFi devices will cover a house quite well, not guaranteed though. Bear in mind if your WiFi antenna is placed down behind the computer case it already has two layers of steel and a wall to penetrate first.
Indoors coverage: We recommend using the low power 2dB antennas and using more wireless repeaters spaced every 100 feet to properly cover an area.
Laptops only transmit 100 feet so there is nothing gained by having a high gain antenna on one end when the laptop can't even talk back more than 100 feet.
Making sure that all repeaters are no more than 100 feet from each other ensures that laptops can always see a repeater or two.
dBm dB(mW): Power relative to 1 milliwatt. When used in audio work the milliwatt is referenced to a 600 ohm load, with the resultant voltage being 0.775 volts. When used in the 2-way radio field, the dB is referenced to a 50 ohm load, with the resultant voltage being 0.224 volts. There are times when spec sheets may show the voltage & power level e.g. -120 dBm = 0.224 microvolts.
"dBm" is used to compare against watts. There is no direct correlation between watts and dBi. dbm is logarithmic and mw is linear.
The term "dB" is not a reference but is rather a method and a measurement standard. dB must be used against a standard, hence "dBm" is used to compare against watts.
net dB added (after cable loss)
Increase in power: Multiple