📡️ Helical Antenna Calculator

A helical antenna is a wire wound like a corkscrew around a support tube. In axial mode it radiates a circularly polarized beam along the axis of the helix, which is why it is the classic feed for satellite downlinks and a popular choice for long-range WiFi links. The geometry is defined by the circumference C = πD of the winding, the pitch S (distance between turns), the pitch angle α = tan&supmin;¹(S/C), and the number of turns N. For axial-mode operation the circumference is usually kept close to one wavelength, roughly 0.75–1.1 λ.

Hand-wound helixes for 2.4 GHz typically use 8–14 turns, a circumference near 0.95λ, and a pitch angle around 12–14°. That combination gives roughly 10–13 dBi of gain with a smooth circular beam. This calculator turns your target frequency into the exact dimensions: wavelength, recommended diameter, circumference, pitch and the predicted free-space gain using the empirical equation G ≈ 8.8 + 10·log₁₀(Cλ²N·S).

The calculator starts from your frequency f and computes the free-space wavelength λ = c/f. From the desired wavelength-based circumference factor (default 0.95) it derives the coil diameter D = C/π. The pitch is then S = C·tanα using your pitch angle, and the total helix length is N×S. The gain estimate follows the empirical axial-mode formula with all lengths expressed in wavelengths.

The derived total helix length is useful when shopping for a support tube, and the wavelength & frequency cross-check helps you confirm the coil geometry before soldering. If you also want to model the link budget end-to-end, pair the result with our Friis path loss calculator or the frequency & wavelength converter.

1. Enter the operating frequency in MHz (for example 2400 for WiFi, 137 for NOAA weather satellites).
2. Set the circumference factor (0.95 is a good default for axial mode).
3. Choose the pitch angle in degrees — typically 12–14°.
4. Enter the number of turns (8–14 for most 2.4 GHz builds).
5. Read the recommended coil diameter, pitch, total length and estimated gain.
6. If needed, adjust the frequency and watch how the dimensions scale.

Why does my helical antenna need a circumference near one wavelength?

Axial-mode radiation relies on the phase advance along each turn. When the circumference is close to one wavelength, the current phase around the turn matches the propagation direction, and the field adds up along the helix axis. Far from this condition the antenna switches to normal mode and radiates like a short dipole instead.

What is the practical gain I can expect?

With 10 turns, C = 0.95λ and α = 13°, the empirical formula predicts about 12 dBi. Real builds typically land within 1–2 dB of that once the SWR is tuned and the reflector is in place.

Is circular polarization worth it for WiFi?

For point-to-point WiFi, linear polarization works and is simpler. Circular polarization pays off when the link involves multipath reflections or moving/rotating stations, and it is essential for most satellite downlinks where Faraday rotation would otherwise cause deep fades.

Can I scale the antenna to another frequency?

Yes — all dimensions scale linearly with wavelength. An antenna built for 915 MHz is exactly 2400/915 ≈ 2.62 times larger than the same design at 2.4 GHz, so you can use this calculator for any band by changing only the frequency.

What should the ground plane or reflector look like?

A flat metal disc 0.8–1.2λ in diameter, or a 4-spoke radial set of similar overall size, mounted 0.1–0.2λ behind the helix end, reduces back lobes and adds 1–2 dB forward gain.

Does wire diameter matter for performance?

Electrically, wire diameter has a small effect on bandwidth and efficiency; mechanically, it decides whether the pitch stays constant. Use wire that is rigid enough to hold shape, and keep the pitch uniform to within a few percent.

Keep the helix circumference between 0.9 and 1.0 λ for a clean axial-mode pattern; values below 0.75 λ start radiating sideways. Mount the helix over a ground plane or a reflector disc of at least 0.8 λ diameter to suppress back radiation. The wire should be rigid enough to hold the pitch constant; soft copper tubing or 2–3 mm solid copper wire works well. For satellite reception the circular polarization is a real advantage because Faraday rotation in the ionosphere no longer causes signal fading. Test with a network analyzer if you can — a proper helix shows a broad SWR dip around the design frequency, not a sharp single-tuned notch.