Documentation

helixMultifilar

Creates bifilar or quadrafilar helix or conical helix antenna on circular ground plane

Description

The helixMultifilar object creates a bifilar or quadrafilar helix or conical helix antenna on a circular ground plane. You can create both short-circuited and open-ended helix multifilar antennas. Bifilar and quadrafilar helix antennas are used in aerospace and defense applications.

The width of the strip is related to the diameter of an equivalent cylinder by the 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 helix antenna is end-fed. The circular ground plane is on the X-Y plane. Helix antennas are commonly used in axial mode. In this mode, the helix circumference is comparable to the operating wavelength, and the helix has maximum directivity along its axis. In normal mode, the helix radius is small compared to the operating wavelength. In this mode, the helix radiates broadside, that is, in the plane perpendicular to its axis. The basic equations for the helix are

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

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

ant = helixMultifilar
ant = helixMultifilar(Name,Value)

Description

example

ant = helixMultifilar creates a bifilar or quadrafilar helix or conical helix antenna operating in the axial mode. The default multifilar helical antenna is end-fed and has a circular ground plane on the X-Y plane. The default operating frequency is around 2 GHz.

example

ant = helixMultifilar(Name,Value) sets properties using one or more name-value pairs. For example, ant = helixMultifilar('Radius',28e-03) creates a multifilar helix with turns of radius 28e-03 m.

Output Arguments

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Multifilar helix antenna, returned as a helixMultifilar object.

Properties

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Number of helical elements, specified as 4 or 2. Specify two elements to create a bifilar helix antenna, and four elements to create a quadrafilar helix antenna.

Example: 'NumArms',2

Example: ant.NumArms = 2

Data Types: double

Radius of the turns, specified as a positive scalar integer in meters or a two element vector with each element unit in meters. In the two-element vector, the first element specifies the bottom radius and the second element specifies the top radius of the conical helix antenna.

Data Types: double

Width of the strip, specified as a positive scalar integer in meters.

Example: 'Width',0.2

Example: ant.Width = 0.2

Data Types: double

Number of turns, specified as a scalar integer.

Example: 'Turns',4

Example: ant.Turns = 4

Data Types: double

Spacing between the turns, specified as a positive scalar integer in meters.

Example: 'Spacing',7.5e-2

Example: ant.Spacing = 7.5e-2

Data Types: double

Status of helix ends, specified as 0 or 1. By default, the helixMultifilar is an open circuit. Setting the property to 1 makes the helix antenna short circuit.

Example: 'ShortEnds',1

Example: ant.ShortEnds = 1

Data Types: double

Direction of the helix turns (windings), specified as 'CW' for clockwise or 'CCW' for counter-clockwise.

Example: 'WindingDirection','CW'

Example: ant.WindingDirection = 'CW'

Data Types: char | string

Height of the feeding stub from the ground plane, specified as a positive scalar integer in meters.

Example: 'FeedStubHeight',7.5e-2

Example: ant.FeedStubHeight = 7.5e-2

Data Types: double

Ground plane radius, specified as a positive scalar integer in meters. By default, the ground plane is on the X-Y plane and is symmetrical about the origin.

Setting this value to Inf uses the infinite ground plane technique for antenna analysis.

Data Types: double

Excitation voltage applied to individual antenna feeds, specified as a scalar integer or vector integers. A scalar value applies the same voltage to all feeds.

Example: 'FeedVoltage',[1 2]

Example: ant.FeedVoltage = [1 2]

Data Types: double

Excitation voltage phase applied to individual antenna feeds, specified as a scalar integer or vector integers. A scalar value applies the same voltage phase to all feeds.

Example: 'FeedPhase',[0 45]

Example: ant.FeedPhase = [0 45]

Data Types: double

Lumped elements added to the antenna feed, specified as a lumped element object handle. You can add a load anywhere on the surface of the antenna. By default, the load is at the origin. For more information, see lumpedElement.

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

Data Types: double

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

Example: 'Tilt',90

Example: 'Tilt',[90 90]'TiltAxis',[0 1 0;0 1 1] tilts the antenna at 90 degree about two three-element vector points in space.

Data Types: double

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'.

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 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

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Create and view a Quadrafilar helix antenna.

ant = helixMultifilar
ant =
helixMultifilar with properties:

NumArms: 4
Width: 1.0000e-03
Turns: 3
Spacing: 0.0350
ShortEnds: 0
WindingDirection: 'CCW'
FeedStubHeight: 1.0000e-03
FeedVoltage: 1
FeedPhase: 0
Tilt: 0
TiltAxis: [1 0 0]

show(ant)

Create and view a bifilar helix antenna.

ant=helixMultifilar('NumArms',2)
ant =
helixMultifilar with properties:

NumArms: 2
Width: 1.0000e-03
Turns: 3
Spacing: 0.0350
ShortEnds: 0
WindingDirection: 'CCW'
FeedStubHeight: 1.0000e-03
FeedVoltage: 1
FeedPhase: 0
Tilt: 0
TiltAxis: [1 0 0]

show(ant)

Create and view a conical multifilar helix antenna of radii, 0.0220 m and 0.00800 m respectively.

ant =
helixMultifilar with properties:

NumArms: 4
Width: 1.0000e-03
Turns: 3
Spacing: 0.0350
ShortEnds: 1
WindingDirection: 'CCW'
FeedStubHeight: 1.0000e-03
FeedVoltage: 1
FeedPhase: 0
Tilt: 0
TiltAxis: [1 0 0]

show(ant)

Plot the pattern of the antenna at 3 GHz.

pattern(ant,3e9)

Overlay the antenna on the pattern.