Far-field Reference Distance Criteria for Compact OTA Testing Ranges

Analyzed are three criteria for the computation of a reference distance marking the start of the far-field region in antenna measurements. The analysis is based on a correction factor for the Friis formula at boresight in the Fresnel zone. Closed form equations are obtained as a function of frequency, the gains of the transmit and receive antennas and a user-defined accuracy factor. Based on the above a far-field reference distance similar to the Fraunhofer distance criterium is defined. The presented results will be essential to design cost-efficient characterization of wireless devices of any size with user-defined accuracy.