# Field from antenna

#### sgr

Joined Jun 27, 2017
17
How to calculate the field from the antenna. For Example I placed the antenna having Gain +ve 2 dBi and the distance is 6 Cm from the enclouser then how much field it will create.

#### LesJones

Joined Jan 8, 2017
3,570
For an isotropic radiator (Antenna) all the power is evenly spread over the surface of a sphere whose radius is the distance from the source. So for your 6 Cm distance all the power is spread over the surface of a sphere radius 6 Cm The area of this is 4πr^2 = 4 * 3.142 * 36 = 452.4 sq cm
So if the transmitter power is 1 watt then the field strength is 1/452.4 Watts per square Cm = 2.2 mW per square Cm For an real antenna you multiply this result by the gain of the antenna with respect to an isotropic antenna. An isotropic antenna is just a concept. It does not physically exist. An antenna achieves it's gain by concentrating the power over a smaller area.

Les

#### sgr

Joined Jun 27, 2017
17
For an isotropic radiator (Antenna) all the power is evenly spread over the surface of a sphere whose radius is the distance from the source. So for your 6 Cm distance all the power is spread over the surface of a sphere radius 6 Cm The area of this is 4πr^2 = 4 * 3.142 * 36 = 452.4 sq cm
So if the transmitter power is 1 watt then the field strength is 1/452.4 Watts per square Cm = 2.2 mW per square Cm For an real antenna you multiply this result by the gain of the antenna with respect to an isotropic antenna. An isotropic antenna is just a concept. It does not physically exist. An antenna achieves it's gain by concentrating the power over a smaller area.

Les
hi
Can you explain field strength in terms of Volt Per Meters (V/m)

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#### WBahn

Joined Mar 31, 2012
26,398
hi
Can you explain field strength in terms of Volt Per Meters (V/m)
It's directly from the definition of an electric field.

If you have two charges separated by some distance (the simplest case with everything else being constructible from it), then they exert a force on each other. In order to move one of the charges from one location to another (from rest to rest, let's say), you have to do some work on it (or it does work on you depending on the direction of the force and the direction of motion). The amount of work per unit charge that has to be done in moving from A to B has units of "joules per coulomb". We define this unit to be the "volt". The amount of work done per unit charge per unit distance is a measure of the field at a particular point in space (and it is a vector quantity, meaning that it also has a direction associated with it) would then have units of "volt per meter".