Characteristic Impedance of High-Frequency Coaxial Line In a high-frequency coaxial transmission line, the characteristic impedance Z0 depends on which physical properties?

Introduction / Context:
Coaxial lines are ubiquitous in RF systems. Their characteristic impedance Z0 determines matching, loss, and bandwidth performance.

Given Data / Assumptions:

• Lossless approximation to reveal first-order dependencies.
• Coax defined by inner radius a and outer radius b, filled with dielectric of relative permittivity εr and permeability close to μr ≈ 1.

Concept / Approach:

For a lossless coax, Z0 = (60 / sqrt(εr)) * ln(b / a) (with μr ≈ 1). Thus Z0 depends on geometry (ratio b/a) and material permittivity εr. Both the insulating material and conductor radii matter.

Step-by-Step Solution:

Verification / Alternative check:

Design calculators for coax dimensions ask for εr and the two radii because both determine Z0.

Why Other Options Are Wrong:

Only-dielectric or only-geometry cannot fully determine Z0; braid angle affects shielding but not the first-order Z0 relation.

Common Pitfalls:

Assuming copper thickness or plating dominates Z0; those affect loss, not the primary impedance.

Final Answer:

both (a) and (b)