Cassegrain Antenna
Cassegrain antennas are a subcategory of reflector
antennas. Reflector antennas have been used fromdiscovery of electromagnetic wave propagation
onwards. The most important applications of reflector
antennas are in radar, space communications, radio
astronomy and wireless communications.
Cassegrain antenna consists of two reflectors (primaryand secondary) and a feeder. The main characteristics
of Cassegrain antennas is their high directivity. The
bigger diameter of antenna reflector is used, the better
gain is achieved.

WIPL-D Simulation
A model of Cassegrain antenna created in WIPL-D Pro
is shown in Fig. 1. We will assume that given antenna
is used for satellite communications in Ka band. A
close-up of the feeder and the primary reflector isshown in Fig. 2. Note that the primary reflector iscurved, unlike in splash-plate reflector antennas.

Figure 2. Cassegrain primary reflector, half antenna
model

Figure 3. Feeder, half antenna model

Figure 1. Cassegrain antenna

In reflector antenna systems, horn antennas are often
used as feeders (Fig. 3). In this project, feeder is
specially designed in order to suppress back radiation.
That was done by adding a choke to horn aperture edge.
Length of choke is equal to quarter of free-space
wavelength (parameter Lam/4 on Fig. 3). Axial twolevel design enables dual mode electromagnetic wave
propagation.

In WIPL-D Pro, reflectors and feeders can be
efficiently designed using built-in parameterized
objects (BoR, Reflector, Circle, ...). One can use (Anti-)
Symmetry feature to reduce the computational burden of
simulation, so in this problem only quarter of theantenna is modeled (Fig. 1). All the antenna parts areconsidered to be perfectly conducting.
Operating frequency is 26.5 GHz (Ka-band).
For model parameters given in Tab. 1, we will calculateantenna gain. In this case, the dish radius is equal to
100 wavelengths, which makes this model challenging
due to its vast electrical size.

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Table 1. Dish radius

Table 2. Simulation data

Parameter

Value [mm]Value[multiplicationwavelength]

Model

No. of unknowns(memory [GB])Time @ 26.5 GHz[min]Dish radius

1132

100quarter

38525 (11.9)

117.2

Radiation pattern in 2D (phi-cut), where phi=0, isshown in Fig. 4. Please note that the theta angle ismeasured with respect to the xOy plane.

Conclusion
WIPL-D Pro offers specialized geometrical objects to
be used as building blocks for complex antenna systemmodels. Reflector shapes can also be imported from a
CAD file, or they can be customized according to auser-defined shape (script file). Hence, practically any
type of a reflector antenna can be easily modeled.
Proper usage of WIPL-D Pro features (for example,Symmetry), enables simulation using only quarter ofstructure, which is very important for analysis ofelectrically big structures, since we reduce memory
used and simulation time dramatically.

Figure 4. Radiation pattern, phi-cut

Number of unknowns, memory requirements, andsimulation time of analysis are given in Tab. 2.
Computer used for these calculations is Intel® Core2
Quad CPU at 2.83 GHz, 8 GB RAM.

Cassegrain antenna of this size is a challenging
simulation task and this sort of antenna is usually
analyzed using geometrical optics methods. However,
WIPL-D Pro successfully simulates this antenna using
very accurate higher order MoM.

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