Ramp response signatures of dielectric targets, especially land mines

The ramp response of a radar target is defined as the far zone backscattered time domain waveform resulting from illumination by a plane electromagnetic wave with a time domain ramp waveshape. It has been shown using physical optics (PO) that the ramp response of a metallic target traces out the transverse cross sectional area of the target along the line-of-sight. The ramp response of a target of simple shape yields information about target size, orientation and geometrical shape. The ramp response of a target is simply the second integral of the impulse response and it emphasizes the lower frequency components of the target backscattered frequency response. This is very important for Ground Penetrating Radar (GPR) applications since the wave attenuation in most soil increases as frequency increases. However, for the dielectric targets, the critical angle and internal scattering mechanisms can change the ramp waveform from the desired transverse cross sectional area. The ramp response signatures of some dielectric targets, especially land mines, have been obtained, with internal scattering mechanisms reduced, from the experimentally measured data for broadside and endfire incidences. The ramp waveforms of these targets obtained from orthogonal look angles have been used to generate their three-dimensional (3-D) images.