Antennas and coverage area

The antennas of wireless devices play a decisive role in determining the design and coverage of wi-fi zone. The main characteristics of each antenna is its gain coefficient, which is measured in dBi. Another characteristic of the antenna is the radiation pattern and thus acceptance. First we will elaborate on how to interpret the value of the gain of the antenna. To do so is theoretically defined, isotropic or isotropic transmitter antenna. It is a point that emits elektromagnitni waves in space equally in all directions and thus have a diagram of spherical radiation. Upon submission of an electromagnetic power to an isotropic radiator, the wave will spread in a spherical shape and fade proportional to the square of the radius of the sphere. In practice, there is an isotropic radiator and each antenna is different from the spherical diagram. This means that, for example antenna radiates more horizontal than vertical or sharply focused is only a sector of the field. Here are a few examples of the radiation pattern of real antennas: Diagram of the dipole (Omni) 2 dBi dipole antenna 5 dBi dipole Diagram Patch Panel Antenna 10 dBi Patch Panel Diagram of a directional antenna 21 dBi parabolic grid The radiation pattern of the antenna means that compared to a radiator rattle, they concentrate more electromagnetic energy in one direction over another. In this sense antenna provides "boost" the signal in a given direction. The gain of the antenna in dB shows exactly how many times greater compared to the isotropic antenna gain and therefore adds "i" (from isotropic) to the unit (dBi). Individual countries introduce legislated restrictions on the power of radiation from radio devices. For wi-fi 802.11 b / g standard in Europe is perceived maximum transmission power of 20 dBm, which is equal to 100mW. This is the maximum allowable equivalent isotropic radiated power (EIRP) for wi-fi devices. EIRP is formed as the sum of the power of the transmitter device, which is typically 17 dBm and the gain of the antenna, usually a dipole and gain 3 dBi. Thus, the total EIRP of 20 dBm or 100 mW. With such power transmission and omni (dipole) antenna, the maximum coverage area with open spaces is about 100 meters at a speed of transmission 1 Mbit / sec. At a speed 11 Mbit / s coverage area reduced to 50 meters. Further reduces the signal in buildings where radio waves are absorbed by concrete walls and reflected by objects and furniture. In many cases the antenna wi-fi device can be replaced with a directional antenna and thus increase the radiated power - EIRP. For example, if the original remove one omni antenna access point and attach strongly focused parabolic antenna gain 21 dBi, then the EIRP will be from 20 dBm to 38 dBm, which equals approximately 6,3 W. With such power can achieve significant transmission distances, but also prejudice and accepted standards of radiation. Just for comparison, in the U.S. the maximum EIRP for standard IEEE 802.11 b / g is 36 dBm, which is equal to 4W.