Waveguide/cavity modes – Identify the incorrect statement about TE/TM transmission Which of the following statements is NOT correct regarding modes used to carry electromagnetic energy in hollow guides and resonant structures?

Introduction:
Electromagnetic energy in hollow metal guides is carried in discrete modes, commonly labeled TE_mn or TM_mn for rectangular guides. The dominant mode is the lowest-cutoff mode that can propagate and is central to practical design.

Given Data / Assumptions:

• Standard empty (air-filled) rectangular waveguide.
• Mode labels follow conventional definitions.
• Focus on conceptual correctness rather than numerical cutoff values.

Concept / Approach:

In TE modes, E_z = 0, so the electric field is everywhere transverse to the propagation direction. In TM modes, H_z = 0, so the magnetic field is everywhere transverse. The subscripts m, n indicate the number of half-wave field variations along the guide's two transverse dimensions. The dominant mode of a rectangular waveguide is TE10, not TM11.

Step-by-Step Solution:

Verification / Alternative check:

Cutoff tables list TE10 with the smallest fc for rectangular guides of given a × b cross-section.

Why Other Options Are Wrong:

Options A, B, C, and E correctly describe TE/TM definitions and the dominant mode for rectangular waveguide.

Common Pitfalls:

Confusing TE vs TM definitions; assuming symmetry implies the same dominant mode across shapes (it does not).

Final Answer:

TM11 is called the dominant mode.