Waveguides vs. Coaxial Lines: Identify the True Advantages Compared to coaxial transmission lines operating at microwave frequencies, which advantages are correctly attributed to metallic waveguides?

Introduction / Context:
At microwave and millimeter-wave frequencies, engineers often choose between coaxial cables and hollow metallic waveguides. Understanding the comparative strengths of waveguides helps in high-power links, radar front-ends, and low-loss feed networks for antennas.

Given Data / Assumptions:

• Frequency is high enough that waveguide TE/TM modes are supported (above cutoff).
• Both media are well-designed and properly matched to minimize reflections.
• Comparison focuses on intrinsic physical limits: power handling, attenuation, and practical construction.

Concept / Approach:

Waveguides confine fields with conducting walls supporting TE/TM modes, while coax supports a TEM mode. Surface current distribution and field strengths drive power handling and loss. Hollow guides avoid dielectric loss (usually air-filled) and distribute current over larger metal areas, usually yielding lower insertion loss and higher breakdown thresholds for a given cross-section at microwave frequencies.

Step-by-Step Solution:

Verification / Alternative check:

Vendor datasheets regularly show lower loss per meter and higher power ratings for standard waveguide bands (e.g., WR-xx) compared to common coax lines at the same frequency.

Why Other Options Are Wrong:

Option D claims waveguides are cheaper and simpler; in practice, coax is cheaper and more flexible. Option E (“all of the above”) includes D and is therefore incorrect. Options A or B alone omit the full set of true advantages, hence C is the best answer.

Common Pitfalls:

Assuming coax is always inferior: at lower microwave frequencies or for flexible runs, high-quality coax can be adequate. Conversely, assuming waveguide bends and twists are trivial—mechanical tolerances matter greatly.

Final Answer:

both (a) and (b) only