Electromagnetic modeling of FOPEN targets and clutter in a lossy half-space

There has been considerable interest in evaluating the use of a low frequency, ultra-wideband (UWB) imaging radar to detect tactical vehicles concealed by foliage. This interest stems from the fact that while high-frequency imagery has shown near-literal imaging capability for targets positioned in open areas, it cannot penetrate tree canopy effectively. However, at low frequencies, the tree canopy is effectively transparent. We examine the issues related to foliage penetrating (FOPEN) radar by first considering VHF scattering from a T-72 tank over soil using a method of moments (MoM) analysis. The MoM analysis considers arbitrary dielectric and perfectly conducting targets in a layered medium, with the lossy, dispersive layers representing the typical layered character of many soils. The solution obtained via the MoM is based on a full-wave formulation of Maxwell's equations. For the clutter, we model both tree trunks as well as a full tree model (trunk and branch structure). The tree trunk is modeled as a dielectric body of revolution (BoR), again using a MoM half-space analysis, while the "tree" is modeled as an arbitrary dielectric target. The scattering of the tank model is compared with the backscatter from typical tree-trunk models. Results show that while the backscatter from the tree trunk is rotationally invariant, the tank scattering is highly aspect dependent, despite the low frequencies considered. Results also show that at certain pose angles, the tree-trunk backscatter is greater than the tank backscatter. The backscatter from the tree model is next compared to the tree-trunk model. Results show that the branch structure can contribute appreciably to the overall backscatter.