On-site Measurement System of Radar Installations successfully tested

As part of the developments in antenna measuring techniques, the Department of High Frequency and Electromagnetic Fields has successfully tested the recently developed sensors for air surveillance radars at airports in Hanover and Wunstorf. Such radar systems are stationary mounted and can therefore neither be measured by means of the antenna scanner nor on the open area test site of PTB. The characterisation of such systems has to be conducted on-site.

Within their research program arcass (advanced remote-controlled airborne sensor systems), the Department of High Frequency and Electromagnetic Fields with project partners from the industry have developed on-site measuring techniques based on an octocopter for several years. The applications of the measuring technique on an unmanned flight system are very diverse and range from the measurement on instrument landing systems (ILS), radio and TV transmitters, the weather radars and wind profiles of the German weather service to the VHF Omnidirectional Radio Range (VOR) of terrestrial flight navigation as well as stationary mounted radar systems.

The octocopter carries newly developed and compact high-frequency measuring instrumentation, which allows the measured signal to be sampled and recorded as a bandpass signal without preprocessing. In addition to the measured data, the time stamp as well as the location information are recorded synchronously. The exact position of the octocopter in the airspace is determined by a precision localization using differential GNSS and displayed in real time to the operator on his smartphone. In addition to the current position, individual measurement data are also processed in real-time so that the operators can easily monitor the measurement process. The octocopter automatically flies on a preprogrammed route and can also hover at measuring points in the space for a time, while recording the time-dependent change of a signal. Because of the compact size of the octocopter, the influence on the electromagnetic field to be measured is minimized. The great advantage of this unmanned aerial system is the property of being able to hover stationary in the ground-level space as well as to be able to specifically target predetermined spatial points. In case of man-carrying helicopters this would be possible only to a limited extent and at significantly higher cost. Due to their minimum speed and the minimum flight altitude, measuring aircraft cannot reach this airspace and can therefore be used only to a limited extent.

A further application of this on-site measuring technique is in the research project WERAN, funded by the Federal Ministry of Economics and Energy on the basis of a decision of the German Bundestag (FZ 0325644A-D). In this case, the possible interaction between wind power plants (wind turbines) and VOR and radars is to be investigated. Together with their project partners, PTB investigates whether and how the navigation or radar signal in the signal transmission channel is modified by wind turbines. On the basis of the change in the signal, the operators of the systems can determine whether disturbance occurs.

Using the new technique, it was thus possible for the first time to test the radar signals at an elevation angle of less than 2 degrees, and at the same time to measure the width of the main lobe, the front-to-back ratio and the side lobe level of the antenna diagram. The recorded radar pulses can be resolved well both in time and spectrally. These data will be made available to manufacturers and operators for further analysis.

Figure: The octocopter after lift-off