# spiralArchimedean

Create Archimedean spiral antenna

## Description

The spiralArchimedean object creates a planar Archimedean spiral antenna on the xy- plane. The default Archimedean spiral is always center fed and has two arms. The field characteristics of this antenna are frequency independent. A realizable spiral has finite limits on the feeding region and the outermost point of any arm of the spiral. The spiral antenna exhibits a broadband behavior. The outer radius imposes the low frequency limit and the inner radius imposes the high frequency limit. The arm radius grows linearly as a function of the winding angle.

The equation of the Archimedean spiral is:

$r={r}_{0}+a\varphi$

where:

• r0 is the inner radius

• a is the growth rate

• ϕ is the winding angle of the spiral

Archimedean spiral antenna is a self-complementary structure, where the spacing between the arms and the width of the arms are equal. The default antenna is center fed. The feed point coincides with the origin. The origin is in the xy- plane.

## Creation

### Description

ant = spiralArchimedean creates a planar Archimedean spiral on the X-Y plane. By default, the antenna operates over a broadband frequency range of 3–5 GHz.

example

ant = spiralArchimedean(Name,Value) sets properties using one or more name-value pairs. For example, ant = spiralArchimedean('Turns',6.25) creates a Archimedean spiral of 6.25 turns.

### Output Arguments

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MATLAB object, returned as scalar spiralArchimedean object.

## Properties

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Number of arms, specified as a scalar integer. You can also create a single arm Archimedean spiral by specifying NumArms is equal to one.

Example: 'NumArms',1

Example: ant.NumArms = 1

Data Types: double

Number of turns of the spiral antenna, specified as a scalar.

Example: 'Turns',2

Example: ant.Turns = 2

Data Types: double

inner radius of the spiral antenna, specified as a scalar in meters.

Data Types: double

Outer radius of the spiral antenna, specified as a scalar in meters.

Data Types: double

Direction of the spiral turns (windings), specified as 'CW' or 'CCW'.

Example: 'WindingDirection','CW'

Example: ant.WindingDirection = CW

Data Types: char | string

Type of the metal used as a conductor, specified as a metal material object. You can choose any metal from the MetalCatalog or specify a metal of your choice. For more information, see metal. For more information on metal conductor meshing, see Meshing.

Example: m = metal('Copper'); 'Conductor',m

Example: m = metal('Copper'); ant.Conductor = m

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

Example: 'Load',lumpedelement. lumpedelement is the object 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 Antennas and Arrays.

Example: Tilt=90

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

Note

The wireStack antenna object only accepts the dot method to change its properties.

Data Types: double

Tilt axis of the antenna, specified as:

• Three-element vector of Cartesian coordinates in meters. In this case, each coordinate in the 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: TiltAxis = 'Z'

Note

The wireStack antenna object only accepts the dot method to change its properties.

Data Types: double

## Object Functions

 show Display antenna, array structures or shapes info Display information about antenna or array axialRatio Axial ratio of antenna beamwidth Beamwidth of antenna charge Charge distribution on antenna or array surface current Current distribution on antenna or array surface design Design prototype antenna or arrays for resonance around specified frequency efficiency Radiation efficiency of antenna 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, dielectric antenna, or array structure meshconfig Change mesh mode of antenna structure optimize Optimize antenna or array using SADEA optimizer 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 rcs Calculate and plot radar cross section (RCS) of platform, antenna, or array returnLoss Return loss of antenna; scan return loss of array sparameters Calculate S-parameter for antenna and antenna array objects vswr Voltage standing wave ratio of antenna

## Examples

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Create and view a 2-turn Archimedean spiral antenna with a 1 mm starting radius and 40 mm outer radius.

show(sa)

Calculate the impedance of an Archimedean spiral antenna over a frequency range of 1-5 GHz.

impedance(sa, linspace(1e9,5e9,21));

Create and view a single-arm Archimedean spiral.

ant = spiralArchimedean;
ant.NumArms = 1
ant =
spiralArchimedean with properties:

NumArms: 1
Turns: 1.5000
WindingDirection: 'CCW'
Conductor: [1x1 metal]
Tilt: 0
TiltAxis: [1 0 0]

show(ant)

## References

[1] Balanis, C.A. Antenna Theory. Analysis and Design, 3rd Ed. New York: Wiley, 2005.

[2] Nakano, H., Oyanagi, H. and Yamauchi, J. “A Wideband Circularly Polarized Conical Beam From a Two-Arm Spiral Antenna Excited in Phase”. IEEE Transactions on Antennas and Propagation. Vol. 59, No. 10, Oct 2011, pp. 3518-3525.

[3] Volakis, John. Antenna Engineering Handbook, 4th Ed. McGraw-Hill

## Version History

Introduced in R2015a