Rectangular waveguide construction: What is the electrical requirement for the wall thickness of the guide relative to the skin depth at the operating frequency?

Introduction:
Skin effect confines RF currents to a thin layer at the conductor surface. Waveguide walls must be thick enough to carry these currents without excessive loss or structural compromise. This question asks how wall thickness relates to the skin depth δ.

Given Data / Assumptions:

• Good conductor (e.g., copper or aluminum) waveguide at microwave frequency.
• Skin depth δ is the current penetration depth where fields decay to 1/e.
• Goal: low conductor loss and mechanical robustness.

Concept / Approach:

Conductor loss and heating decrease as the wall thickness exceeds several skin depths, ensuring the current is fully supported within the conductor without significant field leakage. A practical rule is that thickness should be several times δ; making it less than or equal to δ risks increased loss and potential deformation or RF leakage at seams.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer datasheets and microwave handbooks recommend thicknesses multiple times δ; plating with silver over base metal further lowers loss while retaining adequate thickness.

Why Other Options Are Wrong:

• Less than or equal to δ: leads to higher loss and possible RF leakage.
• Either (b) or (c) or exact multiples (e.g., exactly 2δ) are arbitrary and not general requirements.

Common Pitfalls:

Assuming thicker walls beyond several δ always improve performance; after a few δ, returns diminish and surface conductivity/finish dominate.

Final Answer:

wall thickness is more than skin depth