Electromagnetic wave propagation is TEM in nature. Why?
The correct answer and explanation is:
Electromagnetic waves are classified based on their mode of propagation, and one common mode is the Transverse Electromagnetic (TEM) wave. A TEM wave is a type of electromagnetic wave where both the electric and magnetic fields are perpendicular to the direction of wave propagation. This characteristic is what makes TEM waves unique.
In the case of TEM waves, the electric field oscillates perpendicular to the direction of propagation, and the magnetic field also oscillates perpendicular to the electric field, forming a right angle to each other. These fields are entirely contained within the transverse plane, meaning that they do not have any components in the direction of wave propagation. This is in contrast to other wave propagation modes, like TE (Transverse Electric) and TM (Transverse Magnetic), where one of the fields (either electric or magnetic) has a component along the direction of propagation.
For an electromagnetic wave to propagate in the TEM mode, a specific setup is required. Typically, the TEM mode can only exist in waveguides that have a uniform cross-section, such as coaxial cables, or in open space when the wave is not confined by any medium. In the coaxial cable, for instance, the electric field is between the inner conductor and the outer shield, while the magnetic field forms concentric circles around the conductors. The wave propagates along the axis of the cable, and both fields are entirely transverse to this axis.
In free space, a TEM wave would require perfect symmetry and a uniform distribution of electromagnetic energy to maintain its propagation. In most real-world applications, however, TEM waves are observed in guided media, where the waveguides or transmission lines ensure the proper structure for the fields to remain in the transverse orientation.