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cassegrainOffset

Create offset Cassegrain antenna

Since R2021a

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    Description

    The default cassegrainOffset object creates an offset Cassegrain antenna resonating around 17.8 GHz. The offset Cassegrain antenna is a parabolic antenna, where the feed antenna is mounted off-axis to convex sub reflector and concave main reflector. The asymmetric arrangement of reflectors provides less blockage for waves redirected from main reflector. The advantage of these antennas is high gain, reduced sidelobes and improved cross polarization. The offset Cassegrain antennas are used in satellite communication ground antennas, radar systems, and, radio telescopes among other applications.

    Offset cassegrain antenna geometry, default radiation pattern, and impedance plot.

    Creation

    Syntax

    ant = cassegrainOffset
    ant = cassegrainOffset(Name=Value)

    Description

    ant = cassegrainOffset creates a conical-horn-fed offset Cassegrain antenna with default property values. The default dimensions are chosen for an operating frequency of around 17.8 GHz.

    example

    ant = cassegrainOffset(Name=Value) sets properties using one or more name–value arguments. Name is the property name and Value is the corresponding value. You can specify several name-value arguments in any order as Name1=Value1,...,NameN=ValueN. Properties that you do not specify, retain their default values.

    For example, ant = cassegrainOffset(FocalLength=0.04) creates an offset Cassegrain antenna with the focal length of the main reflector set to 40 mm.

    example

    Properties

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    Exciter antenna or array type, specified as either:

    • Antenna object from the catalog (except reflector type, cavity type and platform-installed antennas)

    • Array object from the catalog (except conformal and infinite arrays)

    • Custom antennas: customAntennaGeometry, customAntennaMesh, customAntenna

    • Measured pattern data of an antenna or array: measuredAntenna

    • Empty array

    To create the reflector backing structure without an exciter, specify this property as an empty array.

    Example: dipole

    Example: rectangularArray(Element=invertedF)

    Example: customAntenna

    Example: measuredAntenna

    Example: []

    Radius of the main and sub reflector, specified as a two-element vector with each element unit in meters. The first element specifies the radius of the main reflector, and the second element specifies the radius of the sub reflector.

    Example: Radius=[0.4 0.2]

    Data Types: double

    Focal length of the main reflector, specified as a positive scalar in meters.

    Example: 0.0850

    Data Types: double

    The distance between the main reflector and x=0 along X-axis, specified as a positive scalar in meters.

    Example: 0.8

    Data Types: double

    The distance between the bottom edge of the main reflector and the top edge of the sub reflector along x -axis, specified as a positive scalar in meters.

    Example: 0.8

    Data Types: double

    Angle between the main reflector and the sub reflector coordinate systems, specified as a positive integer in degrees.

    Example: 8

    Data Types: double

    Tilt angle of the reflectors, specified as a two-element vector with each element unit in degrees. The first element specifies the tilt of the main reflector, and the second element specifies the tilt of the sub reflector.

    Note

    You can use BasisReflectorTilt to obtain initial value of tilt angles of reflectors with respect to reflector dimensions.

    Example: [60 20]

    Data Types: double

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

    Example: 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.

    Data Types: double

    Tilt axis of the antenna, specified as one of these values:

    • 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, specified as a 2-by-3 matrix corresponding to two three-element vectors of Cartesian coordinates. In this case, the antenna rotates around the line joining the two points.

    • "x", "y", or "z" to describe a rotation about the x-, y-, or z-axis, respectively.

    For more information, see Rotate Antennas and Arrays.

    Example: [0 1 0]

    Example: [0 0 0;0 1 0]

    Example: "Z"

    Data Types: double | string

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

    Example: Load=lumpedelement, where lumpedelement is the load added to the antenna feed.

    Example: lumpedElement(Impedance=75)

    Solver for antenna analysis, specified as a string. Default solver is "MoM-PO"(Method of Moments-Physical Optics hybrid). Other supported solvers are: "MoM" (Method of Moments), "PO" (Physical optics) or "FMM" (Fast Multipole Method).

    Example: SolverType="MoM"

    Data Types: string

    Object Functions

    axialRatioCalculate and plot axial ratio of antenna or array
    bandwidthCalculate and plot absolute bandwidth of antenna or array
    beamwidthBeamwidth of antenna
    chargeCharge distribution on antenna or array surface
    currentCurrent distribution on antenna or array surface
    designDesign prototype antenna or arrays for resonance around specified frequency or create AI-based antenna from antenna catalog objects
    efficiencyCalculate and plot radiation efficiency of antenna or array
    EHfieldsElectric and magnetic fields of antennas or embedded electric and magnetic fields of antenna element in arrays
    feedCurrentCalculate current at feed for antenna or array
    impedanceCalculate and plot input impedance of antenna or scan impedance of array
    infoDisplay information about antenna, array, or platform
    memoryEstimateEstimate memory required to solve antenna or array mesh
    meshMesh properties of metal, dielectric antenna, or array structure
    meshconfigChange meshing mode of antenna, array, custom antenna, custom array, or custom geometry
    msiwriteWrite antenna or array analysis data to MSI planet file
    optimizeOptimize antenna or array using SADEA optimizer
    patternPlot radiation pattern and phase of antenna or array or embedded pattern of antenna element in array
    patternAzimuthAzimuth plane radiation pattern of antenna or array
    patternElevationElevation plane radiation pattern of antenna or array
    peakRadiationCalculate and mark maximum radiation points of antenna or array on radiation pattern
    rcsCalculate and plot monostatic and bistatic radar cross section (RCS) of platform, antenna, or array
    resonantFrequencyCalculate and plot resonant frequency of antenna
    returnLossCalculate and plot return loss of antenna or scan return loss of array
    showDisplay antenna, array structures, shapes, or platform
    solverAccess FMM solver settings for electromagnetic analysis
    sparametersCalculate S-parameters for antenna or array
    stlwriteWrite mesh information to STL file
    vswrCalculate and plot voltage standing wave ratio (VSWR) of antenna or array element

    Examples

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    Open Live Script

    Create an offset Cassegrain dual-reflector antenna with default properties. 

    ant = cassegrainOffset
    ant = 
  cassegrainOffset with properties:

                 Exciter: [1x1 hornConical]
                  Radius: [0.3475 0.0650]
             FocalLength: 0.5000
     MainReflectorOffset: 0.5000
         InterAxialAngle: 5
    DualReflectorSpacing: 0.0350
           ReflectorTilt: [53.1300 11.3700]
                    Tilt: 0
                TiltAxis: [1 0 0]
                    Load: [1x1 lumpedElement]
              SolverType: 'MoM-PO'

    View the antenna using the show function.

    show(ant)

    Figure contains an axes object. The axes object with title cassegrainOffset antenna element, xlabel x (mm), ylabel y (mm) contains 7 objects of type patch, surface. These objects represent PEC, feed.

    Plot the radiation pattern of offset Cassegrain dual-reflector antenna at a frequency of 18 GHz.

    pattern(ant,18e9)

    Figure contains 2 axes objects and other objects of type uicontrol. Axes object 1 contains 7 objects of type patch, surface. Hidden axes object 2 contains 19 objects of type surface, line, text, patch.

    Open Live Script

    Create and view offset Cassegrain antenna with optimum reflector tilt angles and with a focal length of 0.8 meters and an interaxial angle of 5 degrees.

    ant = cassegrainOffset(InterAxialAngle=5,FocalLength=0.8)
    ant = 
  cassegrainOffset with properties:

                 Exciter: [1x1 hornConical]
                  Radius: [0.3475 0.0650]
             FocalLength: 0.8000
     MainReflectorOffset: 0.5000
         InterAxialAngle: 5
    DualReflectorSpacing: 0.0350
           ReflectorTilt: [53.1300 11.3700]
                    Tilt: 0
                TiltAxis: [1 0 0]
                    Load: [1x1 lumpedElement]
              SolverType: 'MoM-PO'

    View the antenna using the show function.

    show(ant)

    Figure contains an axes object. The axes object with title cassegrainOffset antenna element, xlabel x (mm), ylabel y (mm) contains 7 objects of type patch, surface. These objects represent PEC, feed.

    View offset cassegrain antenna with optimum reflector tilt angles.

    ant.ReflectorTilt = ant.BasisReflectorTilt
    ant = 
  cassegrainOffset with properties:

                 Exciter: [1x1 hornConical]
                  Radius: [0.3475 0.0650]
             FocalLength: 0.8000
     MainReflectorOffset: 0.5000
         InterAxialAngle: 5
    DualReflectorSpacing: 0.0350
           ReflectorTilt: [34.7080 0.9748]
                    Tilt: 0
                TiltAxis: [1 0 0]
                    Load: [1x1 lumpedElement]
              SolverType: 'MoM-PO'

    View the antenna using the show function.

    show(ant)

    Figure contains an axes object. The axes object with title cassegrainOffset antenna element, xlabel x (mm), ylabel y (mm) contains 7 objects of type patch, surface. These objects represent PEC, feed.

    Calculate the impedance of the antenna over a frequency span 17 GHz - 18 GHz.

    impedance(ant,linspace(17e9,18e9,27))

    Figure contains an axes object. The axes object with title Impedance, xlabel Frequency (GHz), ylabel Impedance (ohms) contains 2 objects of type line. These objects represent Resistance, Reactance.

    Open Live Script

    Create a linear array of bowtie antennas.

    e = bowtieTriangular(Tilt=90,TiltAxis=[0 1 0]);
arr = linearArray(Element=e, ElementSpacing=0.25);

    Create an offset Cassegrain antenna with the linear array as the exciter.

    ant = cassegrainOffset(Exciter=arr)
    ant = 
  cassegrainOffset with properties:

                 Exciter: [1x1 linearArray]
                  Radius: [0.3475 0.0650]
             FocalLength: 0.5000
     MainReflectorOffset: 0.5000
         InterAxialAngle: 5
    DualReflectorSpacing: 0.0350
           ReflectorTilt: [53.1300 11.3700]
                    Tilt: 0
                TiltAxis: [1 0 0]
                    Load: [1x1 lumpedElement]
              SolverType: 'MoM-PO'


    show(ant)
view([-22 1])

    Figure contains an axes object. The axes object with title cassegrainOffset antenna element, xlabel x (mm), ylabel y (mm) contains 9 objects of type patch, surface. These objects represent PEC, feed.

    More About

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    References

    [1] Granet, C. “Designing Classical Offset Cassegrain or Gregorian Dual-Reflector Antennas from Combinations of Prescribed Geometric Parameters.” IEEE Antennas and Propagation Magazine 44, no. 3 (June 2002): 114–123.

    Version History

    Introduced in R2021a

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