Dominant Mode Property in Waveguides: Which characteristic defines the dominant mode in a waveguide?

Introduction / Context:
In waveguides, multiple modes can propagate above their respective cut-off frequencies. The 'dominant mode' is the one that first propagates as frequency increases from zero, a key concept for design and analysis.

Given Data / Assumptions:

• Hollow metallic waveguide (e.g., rectangular), standard mode nomenclature (TE10 is dominant in rectangular waveguides).

Concept / Approach:

The dominant mode is defined as the mode with the lowest cut-off frequency. It requires the smallest operating frequency to propagate and is therefore the most readily excited mode in a given guide geometry.

Step-by-Step Reasoning:

Verification / Alternative check:

Textbook mode tables list TE10 as dominant; corresponding cut-off is lowest for rectangular geometry, validating the definition.

Why Other Options Are Wrong:

• Highest cut-off frequency: opposite of the definition.
• No attenuation / No phase shift / Zero group delay: not defining properties and, in general, not true in realistic guides.

Common Pitfalls:

• Confusing dominant mode property with loss/dispersion characteristics.

Final Answer:

Lowest cut-off frequency