dipoleHelix

Create helical dipole antenna

Description

The dipoleHelix object is a helical dipole antenna. The antenna is typically center-fed. You can move the feed along the antenna length using the feed offset property. Helical dipoles are used in satellite communications and wireless power transfers.

The width of the strip is related to the diameter of an equivalent cylinder by this equation

$$w=2d=4r$$

where:

• w is the width of the strip.

• d is the diameter of an equivalent cylinder.

• r is the radius of an equivalent cylinder.

For a given cylinder radius, use the cylinder2strip utility function to calculate the equivalent width. The default helical dipole antenna is center-fed. The circular ground plane is on the X-Y plane. Commonly, helical dipole antennas are used in axial mode. In this mode, the helical dipole circumference is comparable to the operating wavelength, and has maximum directivity along its axis. In normal mode, the helical dipole radius is small compared to the operating wavelength. In this mode, the helical dipole radiates broadside, that is, in the plane perpendicular to its axis. The basic equation for the helical dipole antenna is:

$$\begin{array}{l}x=r\cos (\theta )\\ y=r\sin (\theta )\\ z=S\theta \end{array}$$

where:

• r is the radius of the helical dipole.

• θ is the winding angle.

• S is the spacing between turns.

For a given pitch angle in degrees, use the helixpitch2spacing utility function to calculate the spacing between the turns in meters.

Creation

Syntax

dh = dipoleHelix

dh = dipoleHelix(Name,Value)

Description

dh = dipoleHelix creates a helical dipole antenna. The default antenna operates around 2 GHz.

dh = dipoleHelix(Name,Value) creates a helical dipole antenna, with additional properties specified by one or more name–value pair arguments. Name is the property name and Value is the corresponding value. You can specify several name-value pair arguments in any order as Name1, Value1, ..., NameN, ValueN. Properties not specified retain their default values.

Properties

Radius — Turn radius

0.0220 (default) | scalar

Turn radius, specified as a scalar in meters.

Example: 'Radius',2

Data Types: double

Width — Strip width

1.0000e-03 (default) | scalar

Strip width, specified as a scalar in meters.

Note

Strip width should be less than 'Radius'/5 and greater than 'Radius'/250. [4]

Example: 'Width',5

Data Types: double

Turns — Number of turns of helical dipole

3 (default) | scalar

Number of turns of the helical dipole, specified a scalar.

Example: 'Turns',2

Data Types: double

Spacing — Spacing between turns

0.0350 (default) | scalar

Spacing between turns, specified as a scalar in meters.

Example: 'Spacing',1.5

Data Types: double

WindingDirection — Direction of helical dipole turns (windings)

'CCW' (default) | 'CW'

Direction of helical dipole turns (windings), specified as 'CW' or 'CCW'.

Example: 'WindingDirection','CW'

Data Types: char | string

Load — Lumped elements

[1x1 lumpedElement] (default) | lumped element object handle

Lumped elements added to the antenna feed, specified as a lumped element object handle. For more information, see lumpedElement.

Example: 'Load',lumpedelement. lumpedelement is the object handle for the load created using lumpedElement.

Example: dh.Load = lumpedElement('Impedance',75)

FeedOffset — Signed distance of feedpoint from origin

0 (default) | two-element vector

Signed distance from center along length and width of ground plane, specified as a two-element vector in meters. Use this property to adjust the location of the feedpoint relative to the ground plane and patch.

Example: 'FeedOffset',[0.01 0.01]

Data Types: double

Tilt — Tilt angle of antenna

0 (default) | scalar | vector

Tilt angle of the antenna, specified as a scalar or vector with each element unit in degrees. For more information, see Rotate Antennas and Arrays.

Example: 'Tilt',90

Example: 'Tilt',[90 90],'TiltAxis',[0 1 0;0 1 1] tilts the antenna at 90 degree about two axes, defined by vectors.

Data Types: double

TiltAxis — Tilt axis of antenna

[1 0 0] (default) | three-element vector of Cartesian coordinates | two three-element vectors of Cartesian coordinates | 'X' | 'Y' | 'Z'

Tilt axis of the antenna, specified as:

• Three-element vectors of Cartesian coordinates in meters. In this case, each vector starts at the origin and lies along the specified points on the X-, Y-, and Z-axes.

• Two points in space, each specified as three-element vectors of Cartesian coordinates. In this case, the antenna rotates around the line joining the two points in space.

• A string input describing simple rotations around one of the principal axes, 'X', 'Y', or 'Z'.

For more information, see Rotate Antennas and Arrays.

Example: 'TiltAxis',[0 1 0]

Example: 'TiltAxis',[0 0 0;0 1 0]

Example: ant.TiltAxis = 'Z'

Object Functions

show	Display antenna or array structure; Display shape as filled patch
info	Display information about antenna or array
axialRatio	Axial ratio of antenna
beamwidth	Beamwidth of antenna
charge	Charge distribution on metal or dielectric antenna or array surface
current	Current distribution on metal or dielectric antenna or array surface
design	Design prototype antenna or arrays for resonance at specified frequency
EHfields	Electric and magnetic fields of antennas; Embedded electric and magnetic fields of antenna element in arrays
impedance	Input impedance of antenna; scan impedance of array
mesh	Mesh properties of metal or dielectric antenna or array structure
meshconfig	Change mesh mode of antenna structure
pattern	Radiation pattern and phase of antenna or array; Embedded pattern of antenna element in array
patternAzimuth	Azimuth pattern of antenna or array
patternElevation	Elevation pattern of antenna or array
returnLoss	Return loss of antenna; scan return loss of array
sparameters	S-parameter object
vswr	Voltage standing wave ratio of antenna

Examples

Helical Dipole Antenna

Create a default helical dipole antenna and view it.

dh = dipoleHelix

dh = 
  dipoleHelix with properties:

              Radius: 0.0220
               Width: 1.0000e-03
               Turns: 3
             Spacing: 0.0350
    WindingDirection: 'CCW'
          FeedOffset: 0
                Tilt: 0
            TiltAxis: [1 0 0]
                Load: [1x1 lumpedElement]

show(dh)

Radiation Pattern of Helical Dipole

Create a four-turn helical dipole antenna with a turn radius of 28 mm and a strip width of 1.2 mm.

dh = dipoleHelix('Radius',28e-3,'Width',1.2e-3,'Turns',4);
show(dh)

Plot the radiation pattern of the helical dipole at 1.8 GHz.

pattern(dh, 1.8e9);

References

[1] Balanis, C. A. Antenna Theory. Analysis and Design. 3rd Ed. Hoboken, NJ: John Wiley & Sons, 2005.

[2] Volakis, John. Antenna Engineering Handbook. 4th Ed. New York: McGraw-Hill, 2007.