Air-traffic control systems

Photo of an air surveillance radar
© Noël Magis -
Results of an interference simulation for an ILS
© IHF/TU Graz
Assessment of aircraft tracks
© IHF/TU Graz


The Institute of Microwave and Photonic Engineering provides a number of research, supporting and engineering services in the area of air-traffic control and surveillance systems. The major tasks are research studies regarding the analysis of surveillance data (from secondary surveillance radars and wide area multilateration systems) and concerning the impacts of interference on radars (e.g. by wind-turbines).

Our main partners are Austro Control GmbH and the Austrian Armed Forces. In the past there were also cooperations with Eurocontrol, ANA (Luxembourg) and skyguide (Switzerland).

Analysis of surveillance data

Assessment of aircraft tracks
© IHF/TU Graz

This includes performance evaluation of surveillance sensors (e.g. radar) by using the recorded output data of the system. Those are normally available in a format called ASTERIX. The analyses are carried out either on sensor- (radar data) or system-level (tracker data) using either existing (e.g. SASS-C suite by Eurocontrol) or self-developed software tools.

Symbolphoto of analysis results of a multilateration system
© IHF/TU Graz

A major project of the last years has been providing support to Austro Control GmbH regarding the implementation of a new sensor-system the so called wide-area-multilateration. Our institute provided independent evaluations necessary for site acceptance tests and system optimization. The figure shows a exemplary - not real data - distribution of the horizontal positional error.

Interference simulations

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

Because air-traffic surveillance systems are essential for safe air-traffic it is necessary to avoid interference to those systems. E.g. the erection of a building in the vicinity of a radar can cause reflections of the radar waves at the fronts of the building which will result in multi-path propagation and in the occurance of a second (ghost) target at an incorrect position on the air-situation display.

Wind-turbines are a major cause for interference to primary radars (not only air-surveillance but also weather-radars) because due to their size and the resulting high radar cross-section they can produce large echo-signals while due to the rotation of the blades the will occure as moving targets. In the worst case this can lead to the loss of real aircraft targets.

Further information on this topic can be found in the section wave propagation.

Aircraft transponder load

© IHF/TU Graz

In the context of a research project IHF studied the load on aircraft transponders. These transponders are interrogated by various systems - secondary surveillance radars (SSR), mode-S radars, multilateration systems (MLAT), collision-avoidance-systems (TCAS) - and respond to those interrogations. Especially MLAT-systems and their typically high numbers of transmitters can produce a heavy load on the transponders resulting in cases where the transponder may not be able to reply which makes the aircraft - for a short time - "invisible". To avoid this, limits for the occupancy of transponders have been introduced.  This project analyzes different airtraffic and infrastructure - deployment of radars - scenarios regarding their influence on the transponder load.

Further information can be found on the TOPAS webpage.

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