Reflector Antennas

Introduction

WIPL-D Pro is a Method of Moments (MoM) based code which enables very accurate EM simulation of arbitrary 3D structures. Among them are antennas in various technologies: wire antennas, horn and aperture antennas, reflector antennas, microstrip antennas, phased array antennas, helical antennas etc. For parabolic reflector antennas, a special type of aperture antennas, MoM based simulation gives more accurate results than approximate techniques based on physical optics PO and/or uniform/geometrical theory of diffraction (UTD/GTD) which are widely used for simulation of dishes.

A model of the reflector is built in WIPL-D Pro using predefined Reflector object editor, shown to the right. Automatic geometry and mesh generation enable creation of parabolic reflector of circular, elliptic or rectangular shape (with or without rounded corners), with central or offset feed. Two types of meshing are available: Classic and Advanced. Advanced meshing is customized for reflectors of circular and elliptical shape and simulation of such reflector requires less unknowns than with classic meshing. This way the simulation time for large reflectors is decreased.

Alternatively, a model of the reflector can be imported from a CAD file, or custom-defined by the user, through a script file.

Example: Cassegrain Antenna

Cassegrain antennas are a subcategory of reflector antennas. Reflector antennas have been used from discovery 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 (primary and 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 is shown in Fig. 2. Note that the primary reflector is curved, unlike in splash-plate reflector antennas.


Figure 1. Cassegrain antenna


Figure 2. Cassegrain primary reflector, half antenna model


Figure 3. Feeder, half antenna model

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 two-level 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 the antenna is modeled (Fig. 1). All the antenna parts are considered to be perfectly conducting.

Operating frequency is 26.5 GHz (Ka-band). For model parameters given in Tab. 1, we will calculate antenna gain. In this case, the dish radius is equal to 100 wavelengths, which makes this model challenging due to its vast electrical size.

Number of unknowns, memory requirements, and simulation time of analysis are given in Tab. 2. Computer used for these calculations is Intel® Core(TM) i7 CPU 950 @3.07 GHz, 24GB RAM, 1 GPU card Nvidia GeForce GTX 470. Simulation was performed using 1 GPU card to achieve the best performance. Radiation pattern in 2D (phi-cut), where phi=0, is shown in Fig. 4. Please note that the theta angle is measured with respect to the xOy plane.

Table 1. Dish radius

Parameter Value [mm] Value [wavelengths]
Dish radius 1132 100

Table 2. Simulation data

Model No. of unknowns Memory [GB] CPU Time @ 26.5GHz [min] GPU Time @ 26.5GHz [min]
quarter 38525 11.06 44.9 11.6


Figure 4. Radiation pattern, phi-cut

Conclusion

WIPL-D Pro offers specialized geometrical objects to be used as building blocks for complex antenna system models. Reflector shapes can also be imported from a CAD file, or they can be customized according to a user-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 of structure, which is very important for analysis of electrically big structures, since we reduce memory used and simulation time dramatically.

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. Simulation time dramatically changes when GPU solution is introduced.

PDF application note

If you have a specific problem in mind and you are not sure if WIPL-D software can handle that problem, contact us. We will analyze your needs and try to help, and if our products satisfy your requirements, we will make you the best possible offer for purchase.