cassegrainOffset

Create offset Cassegrain antenna

Since R2021a

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.

Creation

Syntax

ant = cassegrainOffset

ant = cassegrainOffset(Name=Value)

Description

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

ant = cassegrainOffset(Name=Value) creates an offset Cassegrain antenna, with additional Properties specified by 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 not specified retain their default values. 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

Exciter — Antenna or array to use as exciter

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

Exciter antenna or array type, specified as an antenna object, an array object, measured pattern data of an antenna, or an empty array. To create the reflector backing structure without the exciter, specify this property as an empty array.

Example: dipole

Example: rectangularArray(Element=invertedF)

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, specified as a scalar or vector with each element unit in degrees. For more information, see Rotate Antennas and Arrays.

Example: 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.

Note

The wireStack antenna object only accepts the dot method to change its properties.

Data Types: double

TiltAxis — Tilt axis of antenna

[1 0 0] (default) | three-element vector of Cartesian coordinates | two three-element vectors of Cartesian coordinates | 'X' | 'Y' | 'Z'

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: TiltAxis = 'Z'

Data Types: double

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

show	Display antenna, array structures or shapes
solver	Access FMM solver for electromagnetic analysis
axialRatio	Axial ratio of antenna
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
EHfields	Electric and magnetic fields of antennas; Embedded electric and magnetic fields of antenna element in arrays
impedance	Input impedance of antenna; scan impedance of array
mesh	Mesh properties of metal, dielectric antenna, or array structure
meshconfig	Change mesh mode of antenna structure
optimize	Optimize antenna or array using SADEA optimizer
pattern	Radiation pattern and phase of antenna or array; Embedded pattern of antenna element in array
patternAzimuth	Azimuth pattern of antenna or array
patternElevation	Elevation pattern of antenna or array
rcs	Calculate and plot radar cross section (RCS) of platform, antenna, or array
returnLoss	Return loss of antenna; scan return loss of array
sparameters	Calculate S-parameter for antenna and antenna array objects
vswr	Voltage standing wave ratio of antenna

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: [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)

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: [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)

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)

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: [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])

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