=== Computing Far-Field Characteristics in FDTD ===
Far fields are the asymptotic form the fields when R r → ∞ or k<sub>0</sub>R r >> 1. Under these assumptions, the fields propagate outward as transverse electromagnetic (TEM) waves:
<math> \mathbf{H_H^{ff}(r)} = \frac{1}{\eta_0} \mathbf{ \hat{k} \times E_E^{ff}(r)} </math>
Far fields are typically computed in the spherical coordinate system as functions of the elevation and azimuth observation angles θ and φ. Only far-zone electric fields are normally considered. From a knowledge of the far fields, you can compute the radiation patterns, other radiation characteristics and radar cross section of targets.
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