Theta, phi spherical coordinate system.
Observation point at $(\theta, \phi) = (35^\circ, 70^\circ)$ in the theta, phi coordinate system.

XF uses the theta, phi coordinate system's $\theta$ and $\phi$ values to define far zone observation points and a plane wave's incident direction. In the coordinate system, $\theta$ is defined as the angle between the positive Z-axis and an observation point and has a typical range of 0 to 180 degrees. The $\phi$ angle is defined as being between the positive X-axis and the observation point projected onto the XY plane and its typical range is between 0 and 360 degrees.

Electromagnetic fields can be broken into $\hat\theta$ and $\hat\phi$ vector components at the observation point ($\theta$, $\phi$).

Alpha, epsilon Ludwig 2 coordinate system.
Observation point at $(\alpha, \epsilon) = (50^\circ, 70^\circ)$ in the alpha, epsilon Ludwig 2 coordinate system.

XF uses the alpha, epsilon Ludwig 2 coordinate system's $\alpha$ and $\epsilon$ values to define far zone observation points. In the coordinate system, $\alpha$ is defined as the angle between the positive Z-axis and the observation point projected onto the XZ plane and has a typical range of -90 to 90 degrees. The $\epsilon$ angle is defined as being between the positive Z-axis and the observation point projected onto the YZ plane and its typical range is between 0 and 360 degrees.

Electromagnetic fields can be broken into $\hat\alpha$ and $\hat\epsilon$ vector components at the observation point ($\alpha$, $\epsilon$).

Elevation, azimuth Ludwig 2 coordinate system.
Observation point at $(E, A) = (50^\circ, 70^\circ)$ in the elevation, azimuth Ludwig 2 coordinate system.

XF uses the elevation, azimuth Ludwig 2 coordinate system's $E$ and $A$ values to define far zone observation points. In the coordinate system, $E$ is defined as the angle between the positive Z-axis and the observation point projected onto the YZ plane and has a typical range of -90 to 90 degrees. The $A$ angle is defined as being between the positive Z-axis and the observation point projected onto the XZ plane and its typical range is between 0 and 360 degrees.

At the observation point (E, A), electromagnetic fields can be broken into $\hat E$ and $\hat A$ vector components.