A hollow rectangular waveguide can NOT propagate TEM wave because

Explanation:

1. A waveguide is a special form of transmission line consisting of a hollow, metal tube. The tube wall provides distributed inductance, while the empty space between the tube walls provides distributed capacitance.

2. Waveguides are practical only for signals of extremely high frequency, where the wavelength approaches the cross-sectional dimensions of the waveguide. 

A hollow rectangular waveguide cannot propagate TEM wave because of the following reasons:

1. If a transmission line is made by perfect conductors then propagation of pure TEM wave will be not possible as in TEM wave propagation electron and magnetic field components are perpendicular to the guide axis and its cut-off frequency is zero and TEM wave propagate only along guide axis.

2. A transmission line such that rectangular waveguide and cylindrical waveguide are hollow waveguides in which center conductor (i.e. guide axis) does not exist. Therefore in this TEM wave can not propagate.

Hence option (1) is the correct answer.

Important Points

• A rectangular waveguide is a hollow metal tube with a rectangular cross-section.
• The conducting walls of the waveguide confine the electromagnetic fields and thereby guide the electromagnetic wave.
• Microwave energies propagate the length of the waveguide by the reflection of its sidewalls.