Helical Antenna Calculator

Design axial-mode helical antennas using Kraus formulas. Ideal for satellite and EME links.

What is a helical antenna?

A helical antenna is a coil of wire that catches circularly polarized waves — like a corkscrew catching a spinning ball. Instead of vibrating back and forth like a dipole, the signal spins as it travels. The helix shape matches that spin perfectly.

Why it matters: Used to communicate with satellites, because signals become circularly polarized as they pass through the ionosphere. A helical antenna on the ground stays locked on regardless of how the satellite rotates.

Design Parameters
Kraus axial-mode helix design.

The frequency to design for. Common: 437 MHz (UHF satellite), 1296 MHz (moonbounce).

How many times the wire winds around. More turns = more gain and a narrower beam.

How far apart each turn is, as a fraction of wavelength. 0.25 is the Kraus optimum for maximum gain.

RF Performance
8-turn helix at 437 MHz (axial mode, RHCP)
Gain
14.8 dBi

Note: The Kraus gain formula is known to overestimate by 3–5 dB compared to measurements. For precise designs, use NEC simulation.

Gain (linear)
30.0
Half-Power Beamwidth
36.8°
Axial Ratio
1.0625
Axial Ratio
0.53 dB
Input Impedance
140 Ω
Pitch Angle α
14.04°
Physical Dimensions
Dimension
mminches
Wavelength (λ)
686.5 mm27.028 in
Circumference (C = λ)
686.5 mm27.028 in
Helix Diameter (D)
218.5 mm8.603 in
Turn Spacing (S)
171.6 mm6.757 in
Total Axial Length
1373.0 mm54.055 in
Wire / Turn
707.6 mm27.859 in
Total Wire Length
5.661 m
Ground Plane Diameter (≥ 0.75λ)
514.9 mm / 20.27 in

Axial mode requires circumference ≈ λ. Input impedance ≈ 140 Ω; use a 50 Ω matching strip (metallic strip ≈ λ/4 wide, λ/4 from feed) or coaxial transformer. Ground plane should be flat or slightly conical, diameter ≥ 0.75λ.