Helical Antenna

From Antennas, by John D. Kraus

7.4 Pratical design considerations for the monofilar axial-mode helical antenna

Fig. 7.19

First we create a parametric line as in the previous example :

here, λ = 1 and α = 14°

The parametric line is :

and t1 = 6 in order to create 6 loops

Create a disk at the bottom of the helix

circle diameter = 0.75λ

and the height = circle diameter / 2

create a circle :

center : (0, 0, 0)

positive normal : towards z axis

radius : 0.375

Extrude the line of this circle with a translation of 0.375 towards z

Check the normal, swap if needed.

Collapse the model and repair it.

Electromagnetic properties :

Frequency : 300 MHz

interface properties on the surfaces (default parameters)

Antenna properties on the wire (radius 0.0005)

Voltage source and short-circuit at the junction between the surface and the wire

Generate the mesh, save and run

Computed wire currents :

Computed far field pattern :

In order to check the expected circular polarization, open the far_field_Eteta_phi.txt file. It contains the axial ratio of the radiated field in the axia_r column. Use a third party software to display it (the current version of the user interface is unable to show it directly). The following picture shows the circular polarization (axial ratio = 1) in the main radiation lobe :