Reduction of RCS by Plasma Shielding: 3-D FDTD and Ray Tracing Calculations

Summary form only given. When a plane electromagnetic wave, traveling in free space, falls on an object, it gives rise to a scattered field in all directions. The ratio of the scattered field to the incident field intensity is related to the radar cross-section (RCS). A collisional unmagnetized plasma; which has a complex dielectric constant, can be used as a good absorber of electromagnetic waves over a wide range of frequencies. This absorption leads to a reduction in the RCS. We have performed simulations of this process using the 3-D finite difference time domain (FDTD) method. Apart from absorption we find that plasma-induced refraction of waves away from the scatterer can also play a significant role. While the FDTD technique is quite general, it is rather expensive computationally. Hence, for parametric studies, it is necessary to identify a faster procedure. Plasma refraction can also be studied using the ray tracing technique, which is less computationally demanding. However, it is only valid under certain conditions, e.g. gradient scale lengths being much greater than the wavelength. Hence it is important to identify the conditions under which FDTD and ray tracing results match reasonably well. In this paper, we will present the results of a comparative study of refraction by plasmas, using 3-D FDTD as well as ray tracing