The Spillover Effect on the Directivity Calculation of Reflector Antennas in Planar Near-field Measurements [Measurements Corner]

The knowledge of an antenna´s directivity (or gain) performance is sometimes the most important information in designing a communication link. Depending on the application, one might be interested in a very accurate measure of the directivity value. This paper focuses on the accurate estimation of antenna directivity in planar near-field measurements. Planar near-field chambers are the most natural systems for the measurement of highly directive antennas such as reflectors, the weight and bulkiness of which may prevent one from using any other system. The main drawback of these systems is that only the forward-directed wave emanating from the antenna will be measured. The spillover energy cannot be captured, and therefore the value calculated for the directivity will be higher than the actual value. This paper develops a systematic approach for the accurate measurement of the spillover losses to compensate for the inaccuracies of the directivity calculation.