Analytical Expression for Brewster Effect Prediction in Bistatic Radar Scattering from Sea Surfaces

A dip induced by the Brewster effect exists in the VV-polarized bistatic normalized radar cross section (NRCS) of sea surfaces. The azimuth angle of this dip is determined by the dielectric constant of seawater and the bistatic geometry, unlike the local minimum of the HH-polarized NRCS, which consistently appears at azimuth angles of ±90°. In this paper, an approximate analytical expression is derived to predict the azimuth angle of the Brewster-induced dip for VV polarization. The applicability of the expression for L through W bands is validated based on numerical analysis. To evaluate its accuracy and practical potential, two sets of simulations are conducted. First, using the second-order small-slope approximation (SSA2), the bistatic NRCS of sea surfaces is calculated. Simulation results demonstrate that the expression accurately predicts the NRCS dip under a variety of incidence elevation angles, sea states, and radar frequencies. Second, initial investigations are performed on bistatic radar detection in two composite scenes, which involve, respectively, a cylindrical buoy floating on sea surface and a generic missile low-flying over sea surface. It is seen that in extremely low signal-to-clutter ratio (SCR) cases at small to medium incidence angles, a significant SCR gain might be obtained if bistatic radar detection geometries along the predicted dips are used.