Derivation of Far-field Gain Using a Gain Reduction Effect in the Fresnel Region

A handy method of calculating far-field gain based on the magnitude of the power transmission in a Fresnel region is presented, which can be applied to the phaseless near-field measurement. Due to the short range inside an anechoic chamber, the probe antenna is often placed in the Fresnel region of the antenna under test (AUT). It is well-known that far-field gain of an antenna gradually reduces when one antenna moves to the other one placed in a proximity distance. This fact can be advantageously applied to estimate the far-field gain in a far-field region. The proposed method offers rapid estimation of the far-field gain based on the simple input knowledge such as the probe antenna gain and the magnitude of the power transmission and the separation distance between AUT and probe antenna. The proposed method can be applicable to a wide range of microwave antennas. This feature makes it possible to offer preliminary measurement results and reference parameters of the measurement for the various types of microwave antennas.