How do waveguides work?

Waveguides work by restricting the transmission of energy to one direction and guiding the waves along a specific path. The shape and size of the waveguide determine the type and frequency of the waves that can propagate through it. The waveguide acts as a high-pass filter, allowing only waves above a certain cut-off frequency to pass through. The waves inside the waveguide can have different modes, depending on how the electric and magnetic fields are oriented with respect to the direction of travel. The most common mode is the TEM (Transverse Electric and Magnetic) mode, where both fields are perpendicular to the direction of travel. This mode can only exist in two-conductor transmission lines, such as coaxial cables. In single-conductor waveguides, such as hollow metal tubes or optical fibers, other modes such as TE (Transverse Electric) or TM (Transverse Magnetic) can exist, where either the electric or magnetic field has a component along the direction of travel1