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cassegrainOffset

Create offset Cassegrain antenna

    Description

    The cassegrainOffset object creates an offset Cassegrain antenna. 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

    Description

    example

    ant = cassegrainOffset creates a conical-horn-fed offset Cassegrain antenna with dimensions for a resonant frequency of 17.8 GHz.

    example

    ant = cassegrainOffset(Name,Value) sets Properties using one or more name-value pairs. For example, ant = cassegrainOffset('FocalLength', 0.04) creates an offset Cassegrain antenna with the focal length of the main reflector set to 40 mm.

    Properties

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    Antenna type used as exciter, specified as an antenna or an array object.

    Example: 'Exciter',dipole

    Example: ant.Exciter = dipole

    Example: ant.Exciter = rectangularArray('invertedF')

    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]

    Example: ant.Radius = [0.4 0.2]

    Data Types: double

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

    Example: 'FocalLength',0.0850

    Example: ant.FocalLength = 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: 'MainReflectorOffset',0.8

    Example: ant.MainReflectorOffset = 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: 'DualReflectorSpacing',0.8

    Example: ant.DualReflectorSpacing = 0.8

    Data Types: double

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

    Example: 'InterAxialAngle',8

    Example: ant.InterAxialAngle = 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: 'ReflectorTilt',[60 20]

    Example: ant.ReflectorTilt = [60 20]

    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: ant.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.

    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'.

    For more information, see Rotate Antennas and Arrays.

    Example: 'TiltAxis',[0 1 0]

    Example: 'TiltAxis',[0 0 0;0 1 0]

    Example: ant.TiltAxis = 'Z'

    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: ant.Load = lumpedElement('Impedance',75)

    Solver for antenna analysis, specified as the comma-separated pair consisting of 'SolverType' and 'MoM-PO' or 'PO' (Physical Optics) or 'MoM' (Method of Moments) or 'FMM' (Fast Multipole Method).

    Example: 'SolverType','MOM'

    Data Types: char

    Object Functions

    showDisplay antenna or array structure; display shape as filled patch
    solverAccess FMM solver for electromagnetic analysis
    axialRatioAxial ratio of antenna
    beamwidthBeamwidth of antenna
    chargeCharge distribution on metal or dielectric antenna or array surface
    currentCurrent distribution on metal or dielectric antenna or array surface
    designDesign prototype antenna or arrays for resonance around specified frequency
    EHfieldsElectric and magnetic fields of antennas; Embedded electric and magnetic fields of antenna element in arrays
    impedanceInput impedance of antenna; scan impedance of array
    meshMesh properties of metal or dielectric antenna or array structure
    meshconfigChange mesh mode of antenna structure
    optimizeOptimize antenna or array using SADEA optimizer
    patternRadiation pattern and phase of antenna or array; Embedded pattern of antenna element in array
    patternAzimuthAzimuth pattern of antenna or array
    patternElevationElevation pattern of antenna or array
    rcsCalculate and plot radar cross section (RCS) of platform, antenna, or array
    returnLossReturn loss of antenna; scan return loss of array
    sparametersCalculate S-parameter for antenna and antenna array objects
    vswrVoltage standing wave ratio of antenna

    Examples

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    Create a offset cassegrain dual reflector antenna with default properties.

    ant = cassegrainOffset
    ant = 
      cassegrainOffset with properties:
    
                     Exciter: [1×1 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: [1×1 lumpedElement]
    
    

    View the antenna using the show function.

    show(ant);

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

    pattern(ant,18e9);

    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 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 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 contains 2 objects of type line. These objects represent Resistance, Reactance.

    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 linear array as 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 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.

    Introduced in R2021a