quasi tem

Why the transmission in TEM or quasi TEM mode is required?What will happen if we transmit using non TEM mode?

Regards,
Popsy

TEM mode is prefered because of its simplicity with planar wave solution and TEM wave normally supported by two conductors.

One possibility is that the TEM mode is almost lossless; non-TEM modes have E or H field components in the direction of propagation, thus the attentuation is much larger.

I think dispersion is the main consideration.

MoonShine and loucy have pretty much covered it.

1.) Modes with minimal longitudinal current have the lowest loss and the least dispersion.

2.) For practical structure, this mode is almost always the lowest order mode. (Circular waveguide is the exception.)

3.) Multiple mode behavour is very difficult to predict. Stick with a single mode; this means using the lowest order mode. (Again, except for the circular waveguide.)

(To completely contradict everything I just wrote, let's analyze a stripline with an airgap ... :D)