Most radar systems emit electromagnetic signals to perform their main tasks – the detection and localisation of targets. These electromagnetic emissions can also be received, analysed and used by a third party, for example by an enemy party to a conflict, in order to obtain information such as emitting waveform and operating mode via the radar system and to identify it in this manner. This type of reconnaissance and information collection from electronic signals is described as «electronic intelligence» (ELINT), and the equipment required for this purpose is known as an ELINT receiver.

Traditional radar systems use a set of previously defined waveforms. These can be described by certain parameters, which are known as pulse description words, such as centre frequency, modulation, pulse duration or pulse repetition rate. The reconnaissance of a traditional radar consists of identifying these pulse description words from the emissions. The radar system can be detected with this type of signature and a library of known reference signatures.

Adaptive radar systems

Future adaptive, also known as cognitive, multifunctional radar systems (MFR) are increasingly deviating from this traditional pattern. Thanks to freely programmable signal generators, new radars can adapt their transmission patterns even better to the time-varying environment and the current task or even continuously recalculate their transmission signals. Thanks to this continuous adaptation, these systems are no longer identifiable from their pulse description words by third parties. This thus poses the question of how this type of adaptive MFR can be identified and analysed in the future. New methods must be developed and evaluation for this purpose. A data record of MFR emissions is required as a basis for this.

First trials performed in Thun

In a project as part of the Research Programme «Reconnaissance and Surveillance» and together with the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR), employees from the Specialist Area Sensory Analysis, armasuisse Science and Technology (S+T), performed an experiment this summer at the military training area in Thun. For this purpose, they modified an ELINT receiver such that adaptive radar signals can also be recorded and analysed. armasuisse S+T deployed the adaptive radar network called «miniCODIR» as a simplified model for an adaptive MFR. This system consists of four radar units and a central control computer, which defines the optimal transmission waveform and transmission power for each unit. It can thus optimally perform its main task, the detection and tracking of a target, with as little transmission effort as possible. Thus, for example, not all radar units always transmit, but only the unit which best sees the target to be pursued.

During the experiment, a large amount of data was collected and emissions recorded. In the first step, this signal data is now used to analyse which optimisations «miniCODIR» has performed on the transmission forms. In the second step, the aim is to clarify the purpose for which these optimisations were performed. The radar experts thus hope to be able to understand and analyse the optimisation algorithms of their model system «miniCODIR», using recorded signal data. In follow-up work, it is planned to also generalise the findings in the model system «miniCODIR» in future, adaptive multifunctional radar systems.