Analysis of Signal-to-Noise For Estimating Far Fields from Near Field Measurements

Near-Field (NF) measurements have become the standard approach for estimating far-field (FF) patterns. The measurement system comprises computer controlled robotics and measurements, with the RF measurements via multiple frequency-dependent components: several cables, some of which must physically move during the measurements; connectors, usually including a rotating joint; an amplifier and perhaps other active components; and the free-space path between the probe and the antenna-under-test (AUT) in the presence of scattering and high loss absorber. When the frequencies become high, for example, mmWaves, the calibration process becomes more demanding, with the cable loss limiting the primary measurement parameter, Signal-to-Noise Ratio (SNR). This paper presents a process for configuring the RF measurement system in order to extend its frequency range by optimizing the SNR.