Mechanical construction: What is the typical wall thickness used for rectangular waveguides at microwave frequencies?

Introduction:
Waveguide walls must be thick enough to carry RF surface currents (well beyond the skin depth), maintain structural integrity, and allow fabrication and joining. Typical commercial waveguides use wall thicknesses that are a small fraction of an inch, balancing electrical and mechanical requirements.

Given Data / Assumptions:

• Common WR-series aluminum or copper guides.
• Microwave operation where skin depth is tiny compared to wall thickness.
• Need for machining robustness and flange attachment.

Concept / Approach:

Because skin depth at a few GHz is only a few micrometers for copper, any thickness above several skin depths is electrically adequate. Mechanically, however, the wall must be stiff and allow brazing/bolting; practical products therefore use around 40–100 mils (1 mil = 0.001 inch), which provides strength and manufacturability without unnecessary mass.

Step-by-Step Solution:

Verification / Alternative check:

Vendor datasheets and engineering handbooks corroborate these typical thicknesses across common waveguide families like WR-90, WR-137, etc.

Why Other Options Are Wrong:

• 1–5 mils or 0.1–0.5 mils: too thin for strength and reliable joining.
• 500 mils: overly heavy without electrical benefit.
• Inches-thick walls: impractical and unnecessary.

Common Pitfalls:

Confusing plating thickness (micrometers) with structural wall thickness; plating improves surface conductivity but does not replace wall stiffness.

Final Answer:

about 40–100 mils