Helical Antenna Calculator

How it is calculated

The tool sizes an axial-mode helix with fixed Kraus-style proportions. Frequency f is in MHz and N is the number of turns. First the wavelength is λ = 3×10⁸ / (f × 10⁶) metres. The helix circumference is set to one wavelength, C = λ, and the turn spacing is fixed at S = 0.25 λ. The axial length is N × S, and the gain is G = 10 × log₁₀(6.2 × (C/λ)² × N × S/λ), which with C = λ and S = 0.25 λ simplifies to 10 × log₁₀(1.55 × N) dBi. So gain depends only on the number of turns, while the size scales with wavelength. The tool accepts f from 1 to 300,000 MHz and N from 2 to 1,000; values outside these limits show no result. It uses c = 3×10⁸ m/s and does not include ground-plane size, wire diameter or pitch angle.

Common mistakes

• Entering the frequency in Hz or GHz. The field is MHz, so 435 MHz must be typed as 435, and 2.4 GHz as 2400. A value below 1 is rejected.
• Treating the circumference output as the diameter. The 689.66 mm figure is the length of one turn around, and the diameter is that divided by π.
• Expecting a higher frequency to give higher gain. In this tool gain depends only on the number of turns; a higher frequency just shrinks the whole antenna.
• Entering fewer than two turns, or more than 1,000. The axial-mode formula is only accepted for N between 2 and 1,000, so values outside that range return no result.
• Treating the result as a finished build. Ground-plane size, conductor thickness and the feed matching are not included, and real gain will differ from the idealised figure.