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.

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

expand all

`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`	Design prototype antenna or arrays for resonance around specified frequency or create AI-based antenna from antenna catalog objects
`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`	Mesh properties of metal, dielectric antenna, or array structure
`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 or array using SADEA optimizer
`pattern`	Plot radiation pattern and phase of antenna or array or embedded pattern of antenna element in 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

collapse all

Create Default Offset Cassegrain Dual-Reflector Antenna

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.

Calculate Impedance of Offset Cassegrain Antenna

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.

Create Array-Fed Offset Cassegrain Antenna

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

expand all

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

cassegrainOffset

Description

Creation

Syntax

Description

Properties

`Exciter` — Antenna or array to use as exciter
`hornConical` (default) | antenna object | array object | custom antenna object | `measuredAntenna` object | empty array

`Radius` — Radius of main and sub reflector
`[0.3175 0.0330]` (default) | two-element vector

`FocalLength` — Focal length of main reflector
`0.5` (default) | positive scalar

`MainReflectorOffset` — Distance of center of main reflector along x-axis from x = 0
`0.5` (default) | positive scalar

`DualReflectorSpacing` — Distance between bottom edge of main reflector and top edge of sub reflector along X-axis
`0.035` (default) | positive scalar

`InterAxialAngle` — Angle between main reflector and sub reflector coordinate systems
`5` (default) | positive integer

`ReflectorTilt` — Tilt angle of reflectors
`[53.13 11.37]` (default) | two-element vector

`Tilt` — Tilt angle of antenna
`0` (default) | scalar | vector

`TiltAxis` — Tilt axis of antenna
`[1 0 0]` (default) | three-element vector | 2-by-3 matrix | `"X"` | `"Y"` | `"Z"`

`Load` — Lumped elements
[1x1 `lumpedElement`] (default) | `lumpedElement` object

`SolverType` — Solver for antenna analysis
`"MoM-PO"` (default) | `"MoM"` | `"PO"` | `"FMM"`

Object Functions

Examples

Create Default Offset Cassegrain Dual-Reflector Antenna

Calculate Impedance of Offset Cassegrain Antenna

Create Array-Fed Offset Cassegrain Antenna

More About

BasisReflectorTilt

Parametric Analysis Guidelines

References

Version History

See Also

Topics

cassegrainOffset

Description

Creation

Syntax

Description

Properties

Exciter — Antenna or array to use as exciter hornConical (default) | antenna object | array object | custom antenna object | measuredAntenna object | empty array

Radius — Radius of main and sub reflector [0.3175 0.0330] (default) | two-element vector

FocalLength — Focal length of main reflector 0.5 (default) | positive scalar

MainReflectorOffset — Distance of center of main reflector along x-axis from x = 0 0.5 (default) | positive scalar

DualReflectorSpacing — Distance between bottom edge of main reflector and top edge of sub reflector along X-axis 0.035 (default) | positive scalar

InterAxialAngle — Angle between main reflector and sub reflector coordinate systems 5 (default) | positive integer

ReflectorTilt — Tilt angle of reflectors [53.13 11.37] (default) | two-element vector

Tilt — Tilt angle of antenna 0 (default) | scalar | vector

TiltAxis — Tilt axis of antenna [1 0 0] (default) | three-element vector | 2-by-3 matrix | "X" | "Y" | "Z"

Load — Lumped elements [1x1 lumpedElement] (default) | lumpedElement object

SolverType — Solver for antenna analysis "MoM-PO" (default) | "MoM" | "PO" | "FMM"

Object Functions

Examples

Create Default Offset Cassegrain Dual-Reflector Antenna

Calculate Impedance of Offset Cassegrain Antenna

Create Array-Fed Offset Cassegrain Antenna

More About

BasisReflectorTilt

Parametric Analysis Guidelines

References

Version History

See Also

Topics

`Exciter` — Antenna or array to use as exciter
`hornConical` (default) | antenna object | array object | custom antenna object | `measuredAntenna` object | empty array

`Radius` — Radius of main and sub reflector
`[0.3175 0.0330]` (default) | two-element vector

`FocalLength` — Focal length of main reflector
`0.5` (default) | positive scalar

`MainReflectorOffset` — Distance of center of main reflector along x-axis from x = 0
`0.5` (default) | positive scalar

`DualReflectorSpacing` — Distance between bottom edge of main reflector and top edge of sub reflector along X-axis
`0.035` (default) | positive scalar

`InterAxialAngle` — Angle between main reflector and sub reflector coordinate systems
`5` (default) | positive integer

`ReflectorTilt` — Tilt angle of reflectors
`[53.13 11.37]` (default) | two-element vector

`Tilt` — Tilt angle of antenna
`0` (default) | scalar | vector

`TiltAxis` — Tilt axis of antenna
`[1 0 0]` (default) | three-element vector | 2-by-3 matrix | `"X"` | `"Y"` | `"Z"`

`Load` — Lumped elements
[1x1 `lumpedElement`] (default) | `lumpedElement` object

`SolverType` — Solver for antenna analysis
`"MoM-PO"` (default) | `"MoM"` | `"PO"` | `"FMM"`