Choosing The Right Wifi Antenna
We use Antennas to focus radio waves to transfer the maximum signal energy in the radio wave to the receiving antennas.
Radio waves pass through the air as electromagnetic energy. They consist of two field components radiating as a travelling wave together. The two fields are the electric and magnetic field. They travel in the same direction at right angles to each other. Which means that in normal arbitrary x,y,z coordinates for example the picture shows the Electric field (E field) moving in the vertical x,y plane from left to right while the corresponding magnetic field (B field) moves in phase in the x,z plane also form the left to the right.
In effect the two wave components move in the same direction and reach their minimum and maximum amplitudes at the same time but are separated by a rotational moment of 90 degrees in space along the direction of travel.
Electromagnetic Wave Polarisation
If you imagine this EM wave coming towards you then the wave would appear as a cross with the E field in the vertical direction and the B field in the horizontal direction. By convention the E field component of a EM wave is used to express the property of polarisation of an EM wave.
The direction of the E field defines Polarisation
So as the E component in our example is in the vertical direction the wave is said to have vertical polarisation. If the wave source was rotated through 90 degrees the E field would appear in the horizontal direction and as such would be horizontally polarised.
Matching Antenna Polarisation
In general it is the aim of antennas to match the polarisation of the transmitting source so that they can obtain the maximum signal strength from the electromagnetic wave. Horizontal and vertical polarisation are just special but commonly used forms of general polarisation of antennas. Many antennas are dual polarised so that two simultaneous waves pass together from the radiating antenna,. The receiving antenna is equally dual polarised. In this way the antennas form 2 separate signal paths so that with clever radios and electronics the radio channel can support greater data speeds.
It is now possible to find wireless devices with MIMO (multiple in multiple out) antenna chains. These devices are able to supply a number of separate spacial signal paths which also are able to create wireless connections of much greater speeds than single antennas.
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