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Antenna Modeling and Analysis

This example shows how to construct, visualize and analyze the antenna elements in the Antenna Toolbox.

Define Antenna Element Using the Antenna Library

Define a helix antenna using the helix antenna element in the Antenna Modeling and Analysis library.

hx = helix
hx = 
  helix with properties:

               Radius: 0.0220
                Width: 1.0000e-03
                Turns: 3
              Spacing: 0.0350
     WindingDirection: 'CCW'
       FeedStubHeight: 1.0000e-03
    GroundPlaneRadius: 0.0750
            Conductor: [1x1 metal]
                 Tilt: 0
             TiltAxis: [1 0 0]
                 Load: [1x1 lumpedElement]

Show Structure of Antenna

Use the show function to view the structure of the helix antenna. A helical antenna consists of a helical shaped conductor on a ground plane. The ground plane of the antenna is in the X-Y plane.

show(hx)

Figure contains an axes object. The axes object with title helix antenna element contains 4 objects of type patch, surface. These objects represent PEC, feed.

Modify Properties of Antenna

Modify the following properties of the helix antenna: Radius = 28e-3, Width = 1.2e-3, Number of Turns = 4 Display the properties of the antenna. View the antenna to see the change in structure.

hx = helix('Radius',28e-3,'Width',1.2e-3,'Turns',4)
hx = 
  helix with properties:

               Radius: 0.0280
                Width: 0.0012
                Turns: 4
              Spacing: 0.0350
     WindingDirection: 'CCW'
       FeedStubHeight: 1.0000e-03
    GroundPlaneRadius: 0.0750
            Conductor: [1x1 metal]
                 Tilt: 0
             TiltAxis: [1 0 0]
                 Load: [1x1 lumpedElement]

show(hx)

Figure contains an axes object. The axes object with title helix antenna element contains 4 objects of type patch, surface. These objects represent PEC, feed.

Plot Radiation Pattern of Antenna

Use pattern function to plot the radiation pattern of the helix antenna. The radiation pattern of an antenna is the spatial distribution of power of an antenna. The pattern displays the directivity or gain of the antenna. By default, the pattern function plots the directivity of the antenna.

pattern(hx,1.8e9)

Figure contains an axes object and other objects of type uicontrol. The axes object contains 4 objects of type patch, surface.

Plot Azimuth and Elevation Pattern of Antenna

Use patternAzimuth and patternElevation functions to plot the azimuth and elevation pattern of the helix antenna. This is the 2D radiation pattern of the antenna at a specified frequency.

patternAzimuth(hx,1.8e9)

Figure contains an object of type uicontainer.

figure
patternElevation(hx,1.8e9)

Figure contains an object of type uicontainer.

Calculate Directivity of Antenna

Use Directivity name-value pair in the output of the pattern function to calculate the directivity of helix antenna. Directivity is the ability of an antenna to radiate power in a particular direction. It can be defined as ratio of maximum radiation intensity in the desired direction to the average radiation intensity in all other directions. Note that the antenna Gain and Directivity are measured at a distance of 100*lambda.

Directivity = pattern(hx,1.8e9,0,90)
Directivity = 10.0444

Calculate EHfields of Antenna

Use the EHfields function to calculate the EH fields of the helix antenna. EH fields are the x, y, z components of electric and magnetic fields of an antenna. These components are measured at a specific frequency and at specified points in space.

[E,H] = EHfields(hx,1.8e9,[0;0;1]);

Plot Different Polarizations of Antenna

Use the Polarization name-value pair in the pattern function to plot the different polarization patterns of the helix antenna. Polarization is the orientation of the electric field, or E-field, of an antenna. Polarization is classified as elliptical, linear, or circular. This example shows the Right-Hand Circularly Polarized(RHCP) radiation pattern of the helix.

pattern(hx,1.8e9,'Polarization','RHCP')

Figure contains an axes object and other objects of type uicontrol. The axes object contains 4 objects of type patch, surface.

Calculate Axial Ratio of Antenna

Use the axialRatio function to calculate the axial ratio of the helix antenna. Antenna axial ratio (AR) in a given direction quantifies the ratio of two orthogonal field components radiated in a circularly polarized wave. An axial ratio of infinity, implies a linearly polarized wave. The unit of measure is dB.

ar = axialRatio(hx,1.8e9,20,30)
ar = 24.4335

Calculate Beamwidth of Antenna

Use the beamwidth function to calculate the beamwidth of the antenna. Antenna beamwidth is the angular measure of the antenna pattern coverage. Beamwidth angle is measured in plane containing the direction of main lobe of the antenna.

[bw, angles] = beamwidth(hx,1.8e9,0,1:1:360)
bw = 57.0000
angles = 1×2

    60   117

Calculate Impedance of Antenna

Use the impedance function to calculate and plot the input impedance of helix antenna. Input impedance is a ratio of voltage and current at the port. Antenna impedance is calculated as the ratio of the phasor voltage (which is 1V at a phase angle of 0 deg as mentioned earlier) and the phasor current at the port.

impedance(hx,1.7e9:1e6:2.2e9)

Figure contains an axes object. The axes object with title Impedance contains 2 objects of type line. These objects represent Resistance, Reactance.

Calculate Reflection Coefficient of Antenna

Use the sparameters function to calculate the S11 of the helix antenna. Antenna reflection coefficient, or S_1_1, describes a relative fraction of the incident RF power that is reflected back due to the impedance mismatch.

S = sparameters(hx,1.7e9:1e6:2.2e9,72)
S = 
  sparameters: S-parameters object

       NumPorts: 1
    Frequencies: [501x1 double]
     Parameters: [1x1x501 double]
      Impedance: 72

  rfparam(obj,i,j) returns S-parameter Sij

rfplot(S)

Figure contains an axes object. The axes object contains an object of type line. This object represents dB(S_{11}).

Calculate Return Loss of Antenna

Use the returnLoss function to calculate and plot the return loss of the helix antenna. Antenna return loss is a measure of the effectiveness of power delivery from a transmission line to a load such as antenna. The calculations are displayed in logscale.

returnLoss(hx,1.7e9:1e6:2.2e9,72)

Figure contains an axes object. The axes object with title Return Loss contains an object of type line.

Calculate Voltage Standing Wave Ratio (VSWR) of Antenna

Use the vswr function to calculate and plot the VSWR of the helix antenna. The antenna VSWR is another measure of impedance matching between transmission line and antenna.

vswr(hx,1.7e9:1e6:2.2e9,72)

Figure contains an axes object. The axes object with title VSWR contains an object of type line.

Calculate Current and Charge Distribution of Antenna

Use the charge function to calculate the charge distribution of the helix antenna. Charge distribution is the value of charge on the antenna surface at a specified frequency. Use the current function to calculate the current distribution of the helix antenna. Current distribution is the value of current on the antenna surface at a specified frequency.

charge(hx,2.01e9)

Figure contains an axes object. The axes object with title Charge distribution contains 4 objects of type patch.

figure
current(hx,2.01e9)

Figure contains an axes object. The axes object with title Current distribution contains 4 objects of type patch.

Show Mesh of Antenna

Use the mesh function to create and show a mesh structure of the helix antenna. mesh is used to discretize antenna surface. In this process, the electromagnetic solver can process the geometry and material of the antenna. The shape of the basis or the discretizing element for subdividing the antenna surface is a triangle.

figure
mesh(hx)

Figure contains an axes object and other objects of type uicontrol. The axes object with title Metal mesh contains 2 objects of type patch, surface.

Mesh Antenna Manually

Specify the maximum edge length for the triangles using the 'MaxEdgeLength' name-value pair. This name-value pair meshes the helix structure manually.

figure
mesh(hx,'MaxEdgeLength',0.01)

Figure contains an axes object and other objects of type uicontrol. The axes object with title Metal mesh contains 2 objects of type patch, surface.

Change Meshing to Automatic

meshconfig(hx,'auto')
ans = struct with fields:
     NumTriangles: 914
    NumTetrahedra: 0
         NumBasis: []
    MaxEdgeLength: 0.0100
         MeshMode: 'auto'

See Also:

Antenna Near-Field Visualization

Array Modeling and Analysis

References

[1] Balanis, C.A. "Antenna Theory. Analysis and Design", p. 514, Wiley, New York, 3rd Edition, 2005.