High resolution harmonic radar imaging for safety and security applications

Harmonic radar is used in solving the problem of detecting and localizing electronic devices within a given measurement scene. The underlying measurement principle utilizes the frequency conversion, mixing and harmonics generation of the harmonic radars transmit signal in systems with nonlinear transfer functions. The nonlinearities in the signal transfer behavior of the targets of interest are due to electronic circuit elements and predominantly semiconductor components. Comparable to classic radar imaging techniques, it is possible to generate maps that give knowledge about the presence and the location of electronic devices within the observed scene. This work presents the current research done at the German Aerospace Center (DLR) in the field of harmonic radar. The development of a dual-mode (classic and harmonic radar) measurement system is shown. In addition, we present a signal processing algorithm for harmonic radar imaging based on wideband, pre-steered, frequency-smoothed robust capon direction-of-arrival estimation. The developed algorithm is analyzed and compared to classic imaging techniques using synthetic data. Concluding measurement results show the capabilities of the experimental measurement setup and validate the performance of the devised imaging algorithm and system demonstrator.