Enter your Frequency, Number of Turns, Circumference, and Turn Spacing into the Helical Antenna Calculator to find your Antenna Gain, plus secondary values like Impedance, Wavelength, Diameter, and Axial Length — everything you need to spec out a helical antenna design in one shot.
Antenna Gain
--
Impedance
--
Wavelength
--
Diameter
--
Axial Length
--
Half Power Beam Width
--
For axial mode operation, the optimal circumference is typically one wavelength (1λ). This provides the best circular polarization and radiation pattern characteristics.
More turns increase antenna gain and directivity but also increase the physical length. Generally, 6-12 turns provide a good balance between gain and practical size for most applications.
The standard spacing is 0.25 wavelengths (λ/4) between turns. This spacing optimizes the axial mode operation and maintains proper phase relationships between turns.
Helical antennas typically have an impedance of 140-150 ohms, requiring impedance matching to standard 50-ohm systems. This is usually done with a quarter-wave transformer or matching network.
The ground plane should have a diameter of at least 0.75 wavelengths (3λ/4) for optimal performance. A larger ground plane improves the front-to-back ratio and pattern symmetry.
While helical antennas naturally produce circular polarization in axial mode, they can receive linearly polarized signals with approximately 3dB loss due to polarization mismatch.
The gain calculations are approximations based on established formulas by John Kraus. Real-world performance may vary due to construction tolerances, ground plane effects, and environmental factors.
Wire diameter is not critical for helical antenna performance. Common choices include AWG 12-14 solid copper wire, which provides good mechanical strength and electrical conductivity.