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10 dB rule: Every 10 dB increase in level results in 10 times the power, and every 10 dB decrease in level results in 1/10 the power.

For every 3 dB decrease, the power is cut in half.

3 dB rule: For every 3 dB increase in level, the power is doubled.

Gain of an antenna is a measure of its enhancement of signal strength: Gain is measured by the dBi rating.Ĭalculating Gain from addition of an antenna: 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.Īntenna gain acts on both the transmit power and receiver sensitivity, so you are not only sending your signal further but you are also able to receive much weaker signals within its line of site. Use high power antennas to send a signal long distances to a very specific and focused point. 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. Range & Radiation Patterns of Antennas Radio waves do not penetrate obstacles very well. The E-plane and H-plane are reference planes for linearly polarized antenna.

It can be vertical, horizontal, circular or combinations of these. Polarization of the wireless antenna is the orientation of the wireless signal. This is the type used in wireless repeater systems and it is intended for short range meshed networks and reaches everyone within its range. This diagram shows the relationship between the E and H planes for a vertically polarized omni-directional dipole antenna. 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 directionsĭiagram below shows the radiation pattern of a 2dBi omni-directional dipole antenna (vertically polarized): Intended for short range meshed networks and reaches everyone within its range. 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.Īt right: Radiation pattern of the 2dB omnidirectional antenna at right (bottom pattern in image)Ī low gain (2dB) omnidirectional antenna like this provides a strong signal in every direction Think of the wireless radiation pattern as a fat donut with the antenna sticking through the middle of the donut. The receiving end must be in the wave-path of the antenna: Below: Dipole Wave Pattern of 2dbi, 5dbi, 7dbi, 9dbiĪBOVE: A 9dB antenna can be seen at 4-5 times the distance of the 2dB antenna but it can only be seen within 5 feet of its horizontal beam path. 9dbi - Best if distance is long and AP and client are on the same elevation (horizontal plane).7dbi - Optimal balance between range and elevation.5dbi - If you wish to send your signal over a couple of levels of a building, a 5dbi dipole is more recommendable.2dbi - Best if relative-positioning is on different elevations: Such as different floors of a building.

To send/receive a signal in a particular direction, use a directional antenna.

Omni-directional antennas pickup stray "interference" signals that can degrade performance.Bigger is not always better: Optimal choice of dipole antenna is determined by the relative positions of the access point and the clients, and range.Omni-Directional Antennas Applications, Radiation Patterns & Range