Site Map

Contact RAC

Join RAC



  Log Into Members' Section  
Register Mbr. No.: Password: Forgot your password?

Helix Antenna

Calculator:  Helix Antenna...VE3KL

Input Area
(See Instructions Below)

Frequency [MHz]

Select Model

Select Units

No. of Turns

Gain [dBic]
3 dB Beam Width [degrees]
Length in Wavelengths
Spacing Between Turns
Pitch angle [degrees]
Length of Wire
Width of Ground Plane

What the Calculator Does

This calculator is used to find the gain of an axial-mode non-tapered Helix Antenna and its physical dimensions.  It uses either the classic Kraus model or the Emerson model.

The model can be selected by the user.  The differences in the models is that the Kraus model is an analytic one that assumes the current distribution is constant along the helix.  This leads to a prediction of ever increasing gain as the helix length increases.  The gain from this model increases by 3 dB for every doubling of the length for a fixed pitch angle. On the other hand, the Emerson model which is mainly based on NEC computer simulation accounts for the current distribution in the helix.  The current decreases along the helix which results in a flattening of the gain as the length is increased.  Note that the Emerson model is only valid for a helix between 2 and 7 wavelengths long.

Both models use a square ground plane 0.6 by 0.6 Wavelengths in dimension. However, values between 0.6 and 1.2 Wavelengths can be used.

The Emerson model also predicts a much lower gain than the Kraus model (4 to 5 dB).  
It also results in a greater length than the Kraus model.

Each model has certain constraints as used in the calculator.

The calculator uses a circumference of 1.0 wavelengths and a pitch angle of 12.5 degrees for the Kraus model as used in the ARRL Satellite Experimenters Handbook  The Emerson model uses a fixed spacing between turns of 0.24 wavelengths while the radius varies with the total length of the helix (number of turns).

How to Use the Calculator

Simply input the values of your choice and press calculate.  The clear button resets the calculator.  You must decide on the method to be used.  The Kraus model was developed in the mid 1940's and is quite approximate while also predicting a gain that is too high.  It is useful however, for comparing existing designs in the literature.  The Emerson model is based on extensive numerical modelling.  It produces maximum gain by allowing the helix radius to vary with its length.