cassegrainOffset

Create offset Cassegrain antenna

Since R2021a

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.

Creation

Syntax

ant = cassegrainOffset

ant = cassegrainOffset(PropertyName=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.

ant = cassegrainOffset(PropertyName=Value) sets properties using one or more name–value arguments. PropertyName is the property name and Value is the corresponding value. You can specify several name-value arguments in any order as PropertyName1=Value1,...,PropertyNameN=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.

Properties

Exciter — Antenna or array to use as exciter

hornConical (default) | antenna object | array object | custom antenna object | measuredAntenna object | empty array

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 — Radius of main and sub reflector

[0.3175 0.0330] (default) | two-element vector

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

FocalLength — Focal length of main reflector

0.5 (default) | positive scalar

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

Example: 0.0850

Data Types: double

MainReflectorOffset — Distance of center of main reflector along x-axis from x = 0

0.5 (default) | positive scalar

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

DualReflectorSpacing — Distance between bottom edge of main reflector and top edge of sub reflector along X-axis

0.035 (default) | positive scalar

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

InterAxialAngle — Angle between main reflector and sub reflector coordinate systems

5 (default) | positive integer

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

Example: 8

Data Types: double

ReflectorTilt — Tilt angle of reflectors

[53.13 11.37] (default) | two-element vector

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 — Tilt angle of antenna

0 (default) | scalar | vector

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

TiltAxis — Tilt axis of antenna

[1 0 0] (default) | three-element vector | 2-by-3 matrix | "X" | "Y" | "Z"

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

Load — Lumped elements

[1x1 lumpedElement] (default) | lumpedElement object

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)

SolverType — Solver for antenna analysis

"MoM-PO" (default) | "MoM" | "PO" | "FMM"

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

axialRatio	Calculate and plot axial ratio of antenna or array
bandwidth	Calculate and plot absolute bandwidth of antenna or array
beamwidth	Beamwidth of antenna
charge	Charge distribution on antenna or array surface
current	Current distribution on antenna or array surface
design	Create antenna, array, or AI-based antenna resonating at specified frequency
efficiency	Calculate and plot radiation efficiency of antenna or array
EHfields	Electric and magnetic fields of antennas or embedded electric and magnetic fields of antenna element in arrays
feedCurrent	Calculate current at feed for antenna or array
impedance	Calculate and plot input impedance of antenna or scan impedance of array
info	Display information about antenna, array, or platform
memoryEstimate	Estimate memory required to solve antenna or array mesh
mesh	Generate and view mesh for antennas, arrays, and custom shapes
meshconfig	Change meshing mode of antenna, array, custom antenna, custom array, or custom geometry
msiwrite	Write antenna or array analysis data to MSI planet file
optimize	Optimize antenna and array catalog elements using SADEA or TR-SADEA algorithm
pattern	Plot radiation pattern of antenna, array, or embedded element of array
patternAzimuth	Azimuth plane radiation pattern of antenna or array
patternElevation	Elevation plane radiation pattern of antenna or array
peakRadiation	Calculate and mark maximum radiation points of antenna or array on radiation pattern
rcs	Calculate and plot monostatic and bistatic radar cross section (RCS) of platform, antenna, or array
resonantFrequency	Calculate and plot resonant frequency of antenna
returnLoss	Calculate and plot return loss of antenna or scan return loss of array
show	Display antenna, array structures, shapes, or platform
solver	Access FMM solver settings for electromagnetic analysis
sparameters	Calculate S-parameters for antenna or array
stlwrite	Write mesh information to STL file
vswr	Calculate and plot voltage standing wave ratio (VSWR) of antenna or array element

Examples

Create Default Offset Cassegrain Dual-Reflector Antenna

Create an 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]
              SolverType: 'MoM-PO'

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)

Calculate Impedance of Offset Cassegrain Antenna

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: [1×1 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: [1×1 lumpedElement]
              SolverType: 'MoM-PO'

View the antenna using the show function.

show(ant)

View offset cassegrain antenna with optimum reflector tilt angles.

ant.ReflectorTilt = ant.BasisReflectorTilt

ant = 
  cassegrainOffset with properties:

                 Exciter: [1×1 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: [1×1 lumpedElement]
              SolverType: 'MoM-PO'

View the antenna using the show function.

show(ant)

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

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

Create Array-Fed Offset Cassegrain Antenna

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: [1×1 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: [1×1 lumpedElement]
              SolverType: 'MoM-PO'

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

More About

BasisReflectorTilt

Calculates tilt angles of the reflectors as a starting parameter for the given reflector dimensions, specified as a two-element vector with each element unit in degrees. The first element specifies the tilt angle of the main reflector, and the second element specifies the tilt angle of the sub reflector.

Example: ant.ReflectorTilt = ant.BasisReflectorTilt

Parametric Analysis Guidelines

To understand how the properties of the cassegrainOffset antenna object influence the antenna design, use the following parametric analysis guidelines.

• To increase the operating frequency, use Radius decrease the radius of the reflectors of the cassegrainOffset antenna.

• To increase the gain, select hornCorrugated or hornConicalCorrugated as the exciter for the cassegrainOffset antenna object.

• Gain variation depends on InterAxialAngle and DualReflectorSpacing properties.

• Use property BasisReflectorTilt (read only) to calculate theoretical ReflectorTilt value.

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