cassegrain

Create Cassegrain antenna

Description

The default cassegrain object creates a Cassegrain antenna resonating around 18.35 GHz. A Cassegrain antenna is a parabolic antenna using a dual reflector system. In this antenna, the feed antenna is mounted at or behind the surface of the main parabolic reflector and aimed at the secondary reflector. For more information see, Architecture of Cassegrain Antenna.

Cassegrain antennas are used in applications such as satellite ground-based systems.

Creation

Syntax

ant = cassegrain

ant = cassegrain(Name=Value)

Description

ant = cassegrain creates a conical horn fed Cassegrain antenna with default property values. The default dimensions are chosen for an operating frequency of around 18.35 GHz.

ant = cassegrain(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 = cassegrain(Radius=[0.4 0.22]) creates a Cassegrain antenna with the main reflector with radius 0.4 m and the secondary reflector with radius 0.22 m.

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: linearArray(Element=patchMicrostrip)

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: [0.4 0.2]

Data Types: double

FocalLength — Focal length of main and sub-reflector

[0.2536 0.1416] (default) | two-element vector

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

Example: [0.35 0.2]

Data Types: double

Load — Lumped elements

[1x1 lumpedElement] (default) | lumped element object

Lumped elements added to the antenna feed, specified as a lumped element object. 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. lumpedelement is the object for the load created using lumpedElement.

Example: lumpedElement(Impedance=75)

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

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

Default Cassegrain Antenna and Radiation Pattern

Create and view a Cassegrain antenna.

ant = cassegrain

ant = 
  cassegrain with properties:

        Exciter: [1x1 hornConical]
         Radius: [0.3175 0.0330]
    FocalLength: [0.2536 0.1416]
           Tilt: 0
       TiltAxis: [1 0 0]
           Load: [1x1 lumpedElement]
     SolverType: 'MoM-PO'

show(ant)

Plot the radiation pattern of the antenna at 18.3 GHz.

mesh(ant,maxEdgeLength=14e-3)

figure;
pattern(ant,18.3e9)

Create Array-fed Cassegrain Antenna

Create a rectangular array of crossed dipole antennas.

e = dipoleCrossed(Tilt=90,TiltAxis=[0 1 0]);
arr = rectangularArray(Element=e,Rowspacing=0.03,ColumnSpacing=0.03);

Use the rectangular array arr to excite a Cassegrain antenna.

ant = cassegrain(Exciter=arr)

ant = 
  cassegrain with properties:

        Exciter: [1x1 rectangularArray]
         Radius: [0.3175 0.0330]
    FocalLength: [0.2536 0.1416]
           Tilt: 0
       TiltAxis: [1 0 0]
           Load: [1x1 lumpedElement]
     SolverType: 'MoM-PO'

show(ant)

More About

Parabolic Reflector Antennas

A typical parabolic antenna consists of a parabolic reflector with a small feed antenna at its focus. Parabolic reflectors used in dish antennas have a large curvature and short focal length and the focal point is located near the mouth of the dish, to reduce the length of the supports required to hold the feed structure. In more complex designs, such as the Cassegrain antenna, a sub reflector is used to direct the energy into the parabolic reflector from a feed antenna located away from the primary focal point. Cassegrain provides an option to increase focal length, reducing side lobes. Such type of antennas can be used in satellite communications and Astronomy and other emerging modes of communications

Architecture of Cassegrain Antenna

Cassegrain antenna consists of three structures:

• Primary parabolic reflector

• Hyperbolic concave sub-reflector

• Exciter element

Focus of the main reflector and the near focus of the sub-reflector coincides. The energy is transmitted from the subreflector to the primary parabolic reflector. The parabolic reflector converts a spherical wavefront into a plane wavefront as the energy directed towards it appears to be coming from focus.

Cassegrain Antenna in Receive Mode

In the receive mode, consider that energy in the form of parallel waves is incident up on the reflector system. This energy is intercepted by the main reflector, a large concave surface,and reflected towards the sub-reflector. The convex surface of the sub-reflector collects this energy and directs it towards the vertex of the main dish. If the rays directed towards this main dish are parallel, then the main reflector is parabolic and the sub-reflector is hyperbolic and the rays will focus on a single point. You then place the receiver at this focusing point.

Cassegrain Antenna in Transmit Mode

In the transmit mode, repeat the experiment to find the focusing point as in the receive mode. Place the feed at the focusing point. The feed is usually small and the sub reflector is in the far-field region of the feed. The size of the sub-reflector is large enough that it intercepts most of the radiation from the feed point. Because of the geometry and the shape of the main reflector and the sub-reflector the rays from the main dish are usually parallel.

References

[1] Dandu, Obulesu. "Optimized Design of Axillary Symmetric Cassegrain Reflector Antenna Using Iterative Local Search Algorithm"

[2] Balanis, C.A. Antenna Theory: Analysis and Design. 3rd Ed. New York: Wiley, 2005.

Version History

Introduced in R2019b