Recognition of ground targets with polarimetric seeker radar at 94 GHz

The report investigates the use of radar polarimetry for improving ground target recognition with a mm-wave seeker radar at 94 GHz. Modelling and simulation are used for the investigation, in addition to an experiment of demonstrative character. The scenario is basically static, i.e. no flight simulation is made. Four different box-shaped targets have been generated, on whose contours trihedral and dihedral-type reflectors are distributed to serve as scattering centres. The clutter is modelled on the same principle on a flat surface. Performance statistics have been generated by random draw of the missile azimuth position, keeping elevation and distance constant. Polarimetric features of the radar return are compared with corresponding data in a database of the four targets. The best match gives an estimate of target type and the azimuth angle. The range resolution and the angular density of catalogue data are taken as variable parameters, as is the polarimetric capability of the seeker: two types have been compared, viz. one fully polarimetric, and one operating with horizontal polarization only. Significantly better performance is obtained for the fully polarimetric sensor, which in addition requires high range resolution combined with a small angular increment in catalogue data for acceptable probabilities of correct classification. Ground clutter deteriorates performance severely. The experimental part of the work aims to show that a real system is capable of fulfilling a minimum requirement, viz. to recognize single reflectors of the types used as building blocks in the modelling. To this end, a coherent, fully polarimetric 94 GHz radar has been used to measure the backscatter from 23 single reflectors, treated as unknown objects. A careful polarimetric calibration procedure enabled error-free classification, and raised the possibility of determining the roll-angle of the dihedral-type reflectors with good accuracy.