Electromagnetic waves consist of oscillating electric and magnetic fields travelling through free space at the speed of light.
These fields have magnitude and direction (vectors) and can be horizontal, vertical, at some other angle or even rotating.
The polarisation is the angle of the electric field and also the angle of the rods or wires of the antenna.
Common polarisations are ...
Incorrectly polarised antennas don't work well at all. This can be used to advantage.
For example most high power UHF TV transmissions are horizontally polarised.
Local low power repeater transmitters serving areas of poor reception are often vertically polarised.
This arrangement makes interference between major and local transmitters much less likely.
Vertically Polarised Dipole - Used for the automation of orange orchard irrigation.
Horizontal Polarisation - Yagi Antenna
Vertical Polarisation - Yagi Antenna
Many sewage pumping plants are radio-linked to a central control point for environmental monitoring, pump control and fault reporting. These use UHF vertical polarisation. Interference from horizontally polarised high power TV transmitters is much less likely.