Real-Time 3D Characterization of Antenna Systems

Abstract

The recent development of commercial phased array antennas for 5G at mm-wave frequencies (20 GHz to 60 GHz) introduces new challenges for radiation pattern characterization. Since these systems aim to employ active beamforming to steer the datastream to specific users, a single base station should be capable of deploying multiple beams simultaneously and electronically steer them to track the user. This introduces the need to characterize a large set of parameters and configurations.
As these modules become more cointegrated with the underlying transceiver chain, its internal modules are becoming less accessible and the device should be considered a unique black box for characterization purposes. Since the difficulty of sub-component testing increases, verifying antenna systems must be performed in an over-the-air (OTA) setup for the entire module.
Current antenna characterization utilizes a single probe, which relies on mechanical rotation to move the sensor around the antenna under test (AUT). This is a proven method, but typically takes several hours, depending on the required resolution. This becomes tedious and commercially unaffordable when multiple measurements are required. Furthermore, these systems require additional instruments, e.g. a vector network analyzer (VNA), which significantly increases the cost of the setups.
The concept proposed in this work avoids these drawbacks. It employs a large number of fixed sensing elements, enabling real-time radiation pattern acquisition. This has the potential to significantly reduce measurement time of 5G antenna systems. A key factor is the sampling of the signal right at the antenna probe, in contrast to the expensive VNA commonly used. This results in a lower complexity and cost, since there are significantly less high frequency components compared to other setups.
A prototype of this concept has been developed for two cross-sections of a dome, which provides real-time antenna pattern tracking capabilities. The high level of flexibility allows easy adaptation to different antenna systems. The sensing probes provide direct downconversion at the antenna, eliminating the need for a VNA. Furthermore, an algorithm is made that calculates the required number of sensor nodes depending on the antenna system under test. The high speed, modularity and low cost allow this setup to be an effective option for instantaneous verification of beam-steer capable antenna systems in the development and fabrication. This can ease the predicted antenna measurement bottleneck expected for the broad employment of small-cell 5G networks. The concept can be expanded to include features such as jammer injection and instantaneous error vector magnitude (EVM) measurement.