Complex natural resonance Complex natural resonances 1 Directional patterns (antenna) 1 Features extraction 1 Natural frequencies 1 Nondestructive examination 1 Patterns classification 1 Perturbation method 1 Perturbation techniques 1 Radar antennas 1 Radar measurement 1 Radars antennas 1 Shape 1 Signal processing 1 Spectrum analysis 1 Target Classification 1 Time domain analysis 1 Transient analysis 1 Ultra-wideband (UWB) 1 Ultrawide band 1 Uncertainty analysis 1 Wideband sensing 1 Wireless communications 1 pattern classification 1 radar signal processing 1 spectral analysis 1