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phased.ShortDipoleAntennaElement

Short-dipole antenna element

Description

The phased.ShortDipoleAntennaElement object models a short-dipole antenna element. A short-dipole antenna is a center-fed wire whose length is much shorter than one wavelength. This antenna object only supports polarized fields.

To compute the response of the antenna element for specified directions:

  1. Create the phased.ShortDipoleAntennaElement object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?.

Creation

Syntax

antenna = phased.ShortDipoleAntennaElement
antenna = phased.ShortDipoleAntennaElement(Name,Value)

Description

antenna = phased.ShortDipoleAntennaElement creates the system object, h, to model a short-dipole antenna element.

antenna = phased.ShortDipoleAntennaElement(Name,Value) creates the system object, antenna, with each specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

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Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

Antenna operating frequency range specified as a 1-by-2 row vector in the form of [LowerBound HigherBound]. This vector defines the frequency range over which the antenna has a response. The antenna element has zero response outside this specified frequency range.

Data Types: double

Dipole axis direction, specified as one of 'X', 'Y', 'Z', or 'Custom'. The dipole axis defines the direction of the dipole current with respect to the local coordinate system. 'X' specifies a dipole along the x-axis, 'Y' specifies a dipole along the y-axis, and 'Z' specifies a dipole along the z-axis. An x-axis or y-axis direction is equivalent to a horizontal dipole and a z-axis direction is equivalent to a vertical dipole. When you set the AxisDirection property to 'Custom', you can specify the dipole axis using the CustomAxisDirection property.

Data Types: char

Custom axis direction of the dipole antenna, specified as a real-valued 3-element column vector. Each entry in the vector represents the component of the dipole axis along the x, y, and z axes in the local coordinate system.

Dependencies

To enable this property, set the AxisDirection property to 'Custom'.

Data Types: double

Usage

Description

example

RESP = antenna(H,FREQ,ANG) returns the antenna’s voltage response, RESP, at the operating frequencies specified in FREQ and in the directions specified in ANG. For the short-dipole antenna element object, RESP is a MATLAB® struct containing two fields, RESP.H and RESP.V, representing the horizontal and vertical polarization components of the antenna's response. Each field is an M-by-L matrix containing the antenna response at the M angles specified in ANG and at the L frequencies specified in FREQ.

Input Arguments

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Operating frequency of antenna element, specified as a nonnegative scalar or nonnegative, real-valued, 1-by-L row vector. Frequency units are in Hz.

FREQ must lie within the range of values specified by the FrequencyRange or the FrequencyVector property of the element. Otherwise, the element produces no response and the response is returned as –Inf. Most elements objects use the FrequencyRange property except for phased.CustomAntennaElement, which uses the FrequencyVector property.

Example: [1e8 2e6]

Data Types: double

Azimuth and elevation angles of response directions, specified as a real-valued, 1-by-M row vector or a real-valued, 2-by-M matrix, where M is the number of angular directions. Angle units are in degrees. The azimuth angle must lie in the range –180° to 180°, inclusive. The elevation angle must lie in the range –90° to 90°, inclusive.

  • If ANG is a 1-by-M vector, each element specifies the azimuth angle of the direction. In this case, the corresponding elevation angle is assumed to be zero.

  • If ANG is a 2-by-M matrix, each column of the matrix specifies the direction in the form [azimuth; elevation].

The azimuth angle is the angle between the x-axis and the projection of the direction vector onto the xy plane. This angle is positive when measured from the x-axis toward the y-axis. The elevation angle is the angle between the direction vector and xy-plane. This angle is positive when measured towards the z-axis. See the definition of Azimuth and Elevation Angles.

Example: [110 125; 15 10]

Data Types: double

Output Arguments

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Voltage response of antenna element returned as a MATLAB struct with fields RESP.H and RESP.V. Both RESP.H and RESP.V contain responses for the horizontal and vertical polarization components of the antenna radiation pattern. Both RESP.H and RESP.V are M-by-L matrices. In these matrices, M represents the number of angles specified in ANG, and L represents the number of frequencies specified in FREQ.

Data Types: double

Object Functions

To use an object function, specify the System object™ as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

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beamwidthCompute and display beamwidth of sensor element pattern
directivityDirectivity of antenna or transducer element
isPolarizationCapableAntenna element polarization capability
patternPlot antenna or transducer element directivity and patterns
patternAzimuthPlot antenna or transducer element directivity and pattern versus azimuth
patternElevationPlot antenna or transducer element directivity and pattern versus elevation
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

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Find the response of a short-dipole antenna element at boresight, (0°,0°), and off boresight, (30°,0°). The antenna operates at 256 MHz.

antenna = phased.ShortDipoleAntennaElement(...
    'FrequencyRange',[100 900]*1e6,'AxisDirection','Y');
ang = [0 30;0 0];
fc = 250e6;
resp = antenna(fc,ang)
resp = struct with fields:
    H: [2x1 double]
    V: [2x1 double]

Horizontal response.

disp(resp.H)
   -1.2247
   -1.0607

Vertical response.

disp(resp.V)
     0
     0

Specify a short-dipole antenna with the dipole oriented along the y-axis and operating at 250 MHz. Then, plot the 3-D responses for both the horizontal and vertical polarizations.

antenna = phased.ShortDipoleAntennaElement( ...
    'FrequencyRange',[100e6,600e6],'AxisDirection','Y');
fc = 250.0e6;

Plot the horizontal polarization response.

pattern(antenna,fc,-180:180,[-90:90],'CoordinateSystem','polar', ...
    'Type','powerdb','Polarization','H');

Plot the vertical polarization response.

pattern(antenna,fc,-180:180,[-90:90],'CoordinateSystem','polar', ...
    'Type','powerdb','Polarization','V');

Plot the combined response.

pattern(antenna,fc,-180:180,[-90:90],'CoordinateSystem','polar',...
    'Type','powerdb','Polarization','C');

Specify a short-dipole antenna with the dipole oriented along a custom axis and operating at 250 MHz. Then, plot the 3-D responses for both the horizontal and vertical polarizations.

Create the short-dipole antenna element System object™. An easy way to create a custom axis is to rotate a unit vector using rotation functions.

v = rotx(30)*rotz(45)*[0;0;1];
antenna = phased.ShortDipoleAntennaElement( ...
    'FrequencyRange',[100e6,600e6],'AxisDirection','Custom', ...
    'CustomAxisDirection',v);

Plot the horizontal polarization response.

fc = 250.0e6;
pattern(antenna,fc,-180:180,[-90:90],'CoordinateSystem','polar', ...
    'Type','powerdb','Polarization','H');

Plot the vertical polarization response.

pattern(antenna,fc,-180:180,[-90:90],'CoordinateSystem','polar', ...
    'Type','powerdb','Polarization','V');

Plot the combined response.

pattern(antenna,fc,-180:180,[-90:90],'CoordinateSystem','polar', ...
    'Type','powerdb','Polarization','C');

Algorithms

The total response of a short-dipole antenna element is a combination of its frequency response and spatial response. This System object calculates both responses using nearest neighbor interpolation and then multiplies the responses to form the total response.

References

[1] Mott, H., Antennas for Radar and Communications, John Wiley & Sons, 1992.

Extended Capabilities

Introduced in R2013a