Transverse modes occur because of boundary conditions imposed on the wave by the waveguide. For example, a radio wave in a hollow metal waveguide must have zero tangential electric field amplitude at the walls of the waveguide, so the transverse pattern of the electric field of waves is restricted to those that fit between the walls. For this reason, the modes supported by a waveguide are quantized.
Transverse modes are classified into different types:
TE modes (Transverse Electric) no electric field in the direction of propagation.
TM modes (Transverse Magnetic) no magnetic field in the direction of propagation.
TEM modes (Transverse ElectroMagnetic) neither electric nor magnetic field in the direction of propagation.
Hybrid modes nonzero electric and magnetic fields in the direction of propagation.
Some authors use an alternate notation;
H modes have a magnetic field component in the direction of propagation. H modes are equivalent to TE modes.
E modes have an electric field component in the direction of propagations. E modes are equivalent to TM modes.
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