cassegrain

Create Cassegrain antenna

Description

The cassegrain object creates a Cassegrain antenna. 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 a resonating frequency of 18.51 GHz. This antenna gives maximum gain when operated at 18 GHz.

ant = cassegrain(Name,Value) sets properties using one or more name-value pairs. 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 type used as exciter

hornConical (default) | antenna object | array object

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

Example: 'Exciter',dipole

Example: ant.Exciter = dipole

Example: ant.Exciter = linearArray('patchMicrostrip')

Radius — Radius of main and subreflector

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

Radius of the main and subreflector, 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 subreflector.

Example: 'Radius',[0.4 0.2]

Example: ant.Radius = [0.4 0.2]

Data Types: double

FocalLength — Focal length of main and subreflector

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

Focal length of the main and subreflector, 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 subreflector.

Example: 'FocalLength',[0.35 0.2]

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

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: 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.

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: ant.TiltAxis = 'Z'

Note

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

Data Types: double

SolverType — Solver for antenna analysis

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

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

Example: 'SolverType','MOM'

Data Types: char

Object Functions

show	Display antenna or array structure; display shape as filled patch
solver	Access FMM solver for electromagnetic analysis
axialRatio	Axial ratio of antenna
beamwidth	Beamwidth of antenna
charge	Charge distribution on metal or dielectric antenna or array surface
current	Current distribution on metal or dielectric 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 or 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

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 subreflector

• Exciter element

Focus of the main reflector and the near focus of the subreflector 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 subreflector. The convex surface of the subreflector 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 subreflector 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 subreflector 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 subreflector 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