Forward-Scatter Bistatic RCS of a PEC Sphere: A Mie-Theory Analysis

Abstract

Forward-scatter radar (FSR) represents an extreme bistatic configuration in which the transmitter--target--receiver geometry approaches collinearity, yielding a bistatic angle near $180^\circ$. In this regime, diffraction-dominated scattering can produce bistatic radar cross sections (RCS) that substantially exceed their monostatic counterparts, a property that underpins FS and passive bistatic radar concepts. This paper presents a rigorous electromagnetic study of the bistatic RCS of a perfectly electrically conducting (PEC) sphere using exact Lorenz--Mie theory. The analysis addresses two practical objectives: (i) quantifying the sensitivity of FS enhancement to deviations from the ideal $180^\circ$ bistatic angle as a function of electrical size, and (ii) decomposing the FS response into the canonical Lorenz--Mie polarization channels $S_1$ and $S_2$, thereby establishing a polarization-resolved benchmark. The results, however, are governed by the dimensionless size parameter $ka$ and therefore generalize directly to other frequencies and bistatic configurations. By explicitly relating full-wave simulation results to Babinet-based FS scaling and optical-theorem interpretations in the high-frequency limit, the paper provides a physically transparent benchmark for FS and passive bistatic radar analysis.