# 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.

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.