Beamforming Multi-Element Near-Field Probe Scales to Measuring Large Phased Arrays

Over-the-Air measurements are critical for the validation and test of active antenna arrays required to operate at mmWave frequencies. In [1] a novel over-the-air near-field measurement approach was presented that targets specifically the validation and test of 5G mmWave antenna modules. It provides the equivalent quantities as known from classical chamber-based far-field measurements but with a significantly reduced form factor, at lower costs, and with higher measurement speed. This is accomplished by using an array of near-field probes and an algorithm to map near-field measurements to far-field properties. For measuring the receiver characteristics of an active antenna, the early prototypes of this new technique require a number of instrumentation channels commensurate with the number of near-field probes being used. This may become prohibitively expensive. In this paper we propose an algorithmic extension of the original method that would require only one channel (per polarization) in combination with a beamforming/phase shifting network on the probe array side. We use measurement results to show the effectiveness of the method.