Ridge waveguide interpretation: Which statement best describes a ridge guide relative to a standard rectangular waveguide (same outer size)?

Introduction:
Ridge waveguides add one or two metal ridges to a rectangular guide to modify the field distribution. This geometry is widely used when a lower cutoff frequency and wider bandwidth are desired without drastically increasing the external dimensions.

Given Data / Assumptions:

• Air-filled ridge guide with perfectly conducting walls (first-order model).
• Comparison is to a plain rectangular guide of the same outer cross-section.
• Focus on dominant-mode behavior and bandwidth.

Concept / Approach:

The ridge narrows the gap where the electric field is concentrated, increasing stored electric energy for a given field amplitude. This is equivalent to adding capacitance in the guide's equivalent circuit, hence the description “capacitively loaded.” Consequences include a reduced cutoff frequency and potential impedance-bandwidth improvement.

Step-by-Step Solution:

Verification / Alternative check:

Mode charts and equivalent circuits for ridge guides corroborate the capacitive loading view; measured dispersion confirms reduced cutoff compared to an unridged guide of equal size.

Why Other Options Are Wrong:

• Inductively or resistively loaded: not the principal effect; losses are not intentionally increased.
• Always higher power handling: field crowding near the ridge can limit breakdown; not always higher.
• Removes cutoff: cutoff remains; it is only lowered.

Common Pitfalls:

Assuming better bandwidth implies higher power capacity. In reality, local field intensification around the ridge often reduces breakdown margin.

Final Answer:

Ridge guide is essentially a form of capacitively loaded guide.