Question

Which of the following are the properties of TEM mode in a lossless medium?

1. Its cut-off frequency is zero.

2. Its transmission line is a hollow waveguide.

3. Its wave impedance is the impedance in a bounded dielectric.

4. Its phase velocity is the velocity of light in an unbounded dielectric.

Select the correct answer using the code given below 

1. 1, 2 and 3
2. 1, 3 and 4
3. 1, 2 and 4
4. 2, 3 and 4

Answer 1

Correct Answer - Option 2 : 1, 3 and 4

TEM: Transverse Electric and Magnetic Propagation

In this mode, both electric and magnetic fields are transverse (perpendicular) to the direction of propagation.

For a TEM mode to propagate:

• Two or more conductors are required and the conductors must have infinite conductivity.
• Hollow waveguide without center conductor does not support TEM mode.  
• Uniform isotropic dielectric material and the dielectric must be lossless.
• The cross-section of the transmission line must remain constant.

 

Properties of TEM mode:

• It has a zero cut-off frequency, i.e. the minimum frequency that the waveguide can propagate for propagation is zero.
• Its transmission line is a two-conductor system.
• Its wave impedance is equal to the intrinsic impedance of the medium. i.e. impedance of the bounded dielectric.
• Its phase velocity is the velocity of light in an unbounded dielectric