SNIFT

 SNIFT is the tool for transforming antenna data that have been obtained in a spherical near-field test facility. The accurate and highly stable algorithm generates the spherical wave expansion of the field that can be reconstructed on any other sphere, in particular the far field.

• SNIFT accounts for the influence of the measuring probe when it has a rotationally symmetry – in spherical wave terms the probe pattern contains only m=±1 harmonics.
• The computed field will in all points have an accuracy of 70 dB or better relative to the isotropic level of the field, provided that both the input field is determined with the same accuracy and the sampling theorem is fulfilled.
• Full-sphere measurements is not a requirement; partial-sphere measurements, however, obviously limits the accuracy of the transformed data to a certain angular region.
• The efficient numerical implementation implies that there is no practical limitations on the size of antennas that can be handled.

SNIFT comes with an auxiliary program, ROSCOE, that performs a rotation of the spherical wave coefficients to account for any misalignment between the measurement- and antenna-coordinate systems.