Helix Antenna Pattern

STK Communications provides standard models for helix antennas.

¹Johnson, Richard C, Antenna Engineering Handbook, 3rd ed., New York: McGraw-Hill (1993), chapter 13

²Kraus, John D., Antennas, 2nd ed., New York: McGraw-Hill (1988), chapter 7.

These models are valid under the following conditions:

Only the axial mode of radiation is supported.
The helix has fixed turn spacing.
The helix has uniform diameter (tapered helices are not supported).
The ratio of the circumference of the helix to wavelength is between 0.75 and 1.33.
The turnspace distance is approximately equal to one-quarter of the wavelength.
The pitch turn angle (calculated by STK) is between 12 and 15 degrees.

This antenna uses a polar coordinate system.

The following options are available for Helix antennas:

Field	Description
Design Frequency	This is the frequency of the antenna. The antenna design frequency is independent of the operational frequency of a transmitter, receiver, or radar. Changing the frequency of a transmitter, receiver, or radar does not update an embedded antenna's design frequency, nor vice versa. The design frequency is solely used at antenna configuration time to compute the antenna size from its max gain or beamwidth settings. A mismatch between signal frequency and antenna design frequency typically causes performance degradation.
Diameter	The diameter of the helix.
Efficiency	Specifies the efficiency factor of the antenna, varying from 0 to 100 percent. Since no antenna is perfect, the efficiency factor allows you to specify the degradation in performance. Typical values fall in the range of 70 to 90 percent.
Turn Spacing	The center-to-center distance between the turns of the helix.
Number of Turns	The total number of turns of the helix.
Back-Lobe Gain	You can use back-lobe gain two different ways: A constant gain value from 90 to 270 degrees in elevation from the boresight of the antenna. Modeled as a fraction of the Main-lobe Gain, but in the opposite direction. For example, boresight gain is computed at a 0 degree elevation angle, the back-lobe attenuation factor is applied and the result is used as the gain at the 180 degree elevation angle. The backlobe gain is a mirror image of the forward gain, but with the backlobe gain applied as an attenuation factor. If “Use as main-lobe attenuation” is selected, the attenuation factor is applied on the main-lobe gain and the result is used in the back-lobe direction.

If you use the default frequency of 14.5 GHz (instead of a frequency in the usual range for helix operation), make sure to adjust the above parameters accordingly, e.g. 0.005 m for Diameter, 0.005 m for Turn Spacing and 10-25 as the Number of Turns.

The following illustration shows a helix antenna pattern:

Helix antenna pattern

The radiation gain pattern is assumed to be around the axis of the Helix. Currently, it is calculated up to 90 degrees from the axis. Radiation gain toward the back direction (i.e. more than 90 degrees from the axis) is not calculated.

The default helix antenna values are good for S-band frequencies (1.0-2.5 GHz), the normal operating band for helix antennas. For other frequencies proper helix sizes must be entered.