Setting Up the Model in CADFEKO

Three spheres are solved with a full method of moments (MoM) solution to obtain the backscattered RCS.

The model Three_Spheres_VPol_MoM.cfx contains three spheres with radii r1 = 0.0125 m, r2 = 0.0125 m and r3 = 0.0125 m positioned at points A1 (-0.6, -0.5, 0.2), A2 (0.2, 0, 0) and A3 (0.6, 0.4, 0).

The CADFEKO CF_ISAR_Resolution.lua application macro is used to calculate the required frequency and angular ranges and associated sampling to create a 3.5 m x 3 m (down-range x cross-range) ISAR image with 0.05 m resolution in both down-range (X) and cross-range (Y). The application macro calculates the required start frequency (f1), end frequency (f2) and the number of frequency samples (nf) for a given centre frequency (f0). It also calculates the required start angle (phi1), end angle (phi2) and angular increment (dphi). The application macro assumes that the polar to Cartesian interpolation will be applied to the RCS data.

Figure 1. The ISAR Resolution and Range dialog.

The XY_plane solution configuration uses the above-mentioned angular and frequency variables to create a plane wave excitation (XY_v0) in the global coordinate system with the ISAR view direction along the X axis.

The UV_plane solution configuration uses the same angular and frequency variables in its plane wave excitation (UV_v0), but the excitation is defined using a local workplane. The workplane is obtained from the XY workplane, rotating it by 20° around the local N axis and then by 10° around the local V axis.

Each configuration contains a far field request set to calculate fields in the plane wave incident direction.

Figure 2. Top view of the XY_plane solution configuration (left) and normal view of the UV_plane solution configuration (right) showing the positions of the three spheres with the plane wave excitation. The yellow frame dimensions are 3.5 m x 3 m.