90 GHz, 3-D Scattered Field Measurements for Investigation of Foreign Object Debris

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Scattering properties of millimeter waves (mmW) remain relatively unknown compared to lower frequency bands, although their study is of interest considering the increasing number of civil applications, especially in the $W$ -band. In this communication, we present an efficient measurement setup that provides scattering measurements with spatial and polarization diversities. The targeted application is foreign object debris (FOD) detection and identification for surveillance of airport runways. Most existing systems are monostatic but rapid advances in mmW technology pushes toward the deployment of multistatic radars on either side of airport runways. In the following, we investigate the contribution of multistatic measurements with a special focus on the reconstruction of glass and brake pad debris, courtesy of DGAC (French civil aviation). We also present an efficient approach for making images of FODs. For this, we process scattered field measurements with an additive (with respect to polarization) backpropagation algorithm. First images include all measured points taken from the upper hemisphere. In order to get closer to the final application, we restrict the field of view to receivers facing the transmitter. Both approaches provide very good shape reconstruction of the glass debris and the central zone of the brake pad. To the best of our knowledge, this is the first time that full-3-D measurements have been conducted on FODs in the $W$ -band. It is also the first example of a 3-D qualitative image of FOD obtained from measured data in the $W$ -band.