Helical Antenna — Axial Mode
The axial-mode helix radiates a circularly-polarised beam along its axis. It operates when the circumference C ≈ λ (pitch angle ~14°). Gain increases with number of turns N. Use Design mode to get optimal dimensions for a target frequency, or Analysis mode to evaluate a specific geometry.
Equations & Parameters ▸
\(G \approx 15N\!\left(\frac{C}{\lambda}\right)^{\!2}\!\frac{S}{\lambda} \quad \text{HPBW} \approx \frac{52°}{(C/\lambda)\sqrt{N\cdot S/\lambda}} \quad Z_{\rm in}\approx 140\,\frac{C}{\lambda}\,\Omega\)
| C = πD | Helix circumference; axial mode: C ≈ λ (C/λ = 0.75–1.33) |
| S | Axial spacing per turn; optimal ≈ λ/4, pitch angle α ≈ 14° |
| N | Number of turns; more turns = higher gain |
| Zin | Input impedance ≈ 140 C/λ Ω; use λ/4 transformer to match to 50 Ω |
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Results
Diagram