Aviation Polarisation RNAV

When an electromagnetic wave is generated, it has two components. The electric part is in the same plane as the aerial and the magnetic wave is perpendicular to this plane. If you imagine a mast emerging vertically from the sea, the electric wave is the sea itself, moving up and down vertically (just as the mast is "up and down" vertically) whereas the magnetic wave would be side to side, like a sea snake swimming away from the mast. This polarisation is important as the receiver will will receive at best efficiency if it has the same polarisation as the transmitting aerial. Problems can be caused if signals arrive with a different polarisation to that of the aerial - see, for example, night effect for an NDBNDB —Non-Directional Beacon. To ensure all aviation is working to a common standard, radio waves in aviation are vertically polarised.

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Which way are electromagnetic waves polarised in aviation?