Wave propagation


3D - Visualisation of the antenna gain of a Yagi-Uda antenna
© IHF/TU Graz
Calculated coverage diagram of a multilateration system in an alpine setting
© IHF/TU Graz
Results of an interference simulation for an ILS
© IHF/TU Graz

General

Wave propagation problems need often electromagnetic field simulations. Especially the interference caused by scattering objects (like buildings or wind turbines) and its impact on radar systems in air-traffic control and meteorology has been subject of several research assignments in the past.

The frequencies covered in those studies lie mainly in the microwave band, but also in the VHF- and UHF-bands (ILS).

Reflections and interference

Simulation result of reflections of a radar beam caused by a high building
© IHF/TU Graz

One of the most important reasons for performance degradation of air-surveillance radars (but also of other radio systems) are reflections with the resulting multi-path propagation causing interference. Those reflections may occur at large structures like buildings or wind turbines. The figure on the left shows the calculated reflections of the signal of a secondary surveillance radar (1030 MHz) at a tower building a few kilometres west of the radar. Additionally the beam on the left side of the figure is caused by the shadowing.  

Simulated difference between an undisturbed and an disturbed antenna diagram
© IHF/TU Graz

Such interference will also affect the antenna diagram. This figure shows the result of simulations how the horizontal diagram of an antenna changes when the beam is in the general direction of a steel tower located nearby.

Results of an interference simulation for an ILS
© IHF/TU Graz

A further example is the simulation of the interference of an instrument landing system (ILS) caused by aircraft moving on nearby taxiways or parked on the apron. The aim of this study was to determine which areas have to be kept free during the critical part of the approach.

Antenna- and field-simulations

For electromagnetic field simulations we use for research and teaching (beside other software tools) the program suite CST STUDIO SUITE ™. The animation below shows the calculated absolute E-field intensity of a Yagi-Uda-array at 150 MHz:

3D - Visualisation of the antenna gain of a Yagi-Uda antenna
© IHF/TU Graz

The resulting 3D-radiation diagram of the same antenna:

Radar and radio coverage

Calculated coverage diagram of a multilateration system in an alpine setting
© IHF/TU Graz

When siting radars (or wireless radio systems in general) it is important to prevent possible shadowing caused by mountains. While lower frequencies (like FM-radio) propagate into the optical shadow area behind the obstacle due to diffraction, this mechanism is negligible at microwave frequencies and above. Therefore the antenna site has to be selected carefully with the help of the so-called coverage diagrams.

This picture shows the coverage of the Inn valley around Innsbruck airport provided by the local multilateration system 5000 ft above sealevel.

Precipitation scattering

Results of scattering calculations for precipitation particles
© IHF/TU Graz

As part of the research the scattering properties of precipitation particles (rain drops, snow flakes, ice crystals and hail) have been calculated for microwave- and mm-wave frequencies.

Contact
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Helmut Schreiber
Dipl.-Ing. Dr.techn.
Phone
+43 316 873 - 7930
Fax
+43 316 873 - 7941