# Limitations of the phase_centre_utility

The phase centre utility has limitations on the θ angle directions, far field point spacing and far field beam direction.

These limitations of the phase centre calculation should be noted:

- At least three distinct θ directions are required that are closely spaced. (There is no limitation on ϕ directions.)
- The far field points should be adequately spaced to allow accurate interpolation of the far field phase. One degree spacing should be sufficient for most cases.
- The far field beam should not be along the Z axis. Better results are expected when the beam is in or close to the XY plane. (This is done by simply rotating the geometry prior to the far field calculation or using a local workplane for the far field request.)

If the results are not in the range that you expected, ensure that the correct far field component has been selected and that the beam does not point along the Z axis. If these are both correct, it could be that the far field has not been sampled finely enough to reconstruct the phase of the far field.