How do conductors and skin effect affect antennas?
At radio frequencies current flows in a thin layer at a conductor’s surface, of thickness given by the skin depth δ = 1/√(πfμσ). For copper, δ is about 2.1 µm at 1 GHz and 66 µm at 1 MHz. The resulting surface resistance Rs = 1/(σδ) sets conductor loss, which matters most in electrically small antennas whose radiation resistance is tiny.[1][2]
How large is skin depth?
| Frequency | Copper skin depth |
|---|---|
| 1 MHz | ≈ 66 µm |
| 10 MHz | ≈ 21 µm |
| 100 MHz | ≈ 6.6 µm |
| 1 GHz | ≈ 2.1 µm |
| 10 GHz | ≈ 0.66 µm |
Calculated from σ = 5.8 × 10⁷ S/m.[1]
Does plating matter?
Yes when plating thickness is comparable to skin depth: current flows mostly in the plating. Silver and gold plating have low resistivity; nickel underplating is ferromagnetic and lossy, so it is avoided at the RF surface in low-loss and low-PIM designs. Surface roughness comparable to δ increases loss at microwave frequencies.[1]
When does conductor loss dominate?
In small loops, meandered lines, normal-mode helices and loaded HF antennas, where Rr is comparable to or smaller than Rloss. Thicker conductors, wider traces, higher-conductivity metals and reducing current density with top loading improve efficiency.[2][3]
Frequently asked questions
Is a hollow tube as good as a solid rod?
At RF, yes, because current flows on the outer surface.
Does aluminum work for antennas?
Yes; its conductivity is about 60% of copper’s, adequate for most antennas.
Why is stainless steel used for whips?
Strength and corrosion resistance; its higher loss is usually acceptable for resonant whips.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “Electrically Small, Superdirective, and Superconducting Antennas”. R. C. Hansen, Wiley. 2006.