Low Cost Millimetre Wave Over-the-Air Testing Method For 5G and Beyond

Abstract

In order to deliver the high capacity and throughput goals for 5G and beyond wireless connectivity,the effective use of Millimetre Wave (mmWave) spectrum is necessary. When compared to sub-6GHz spectrum, these higher frequencies incur greater attenuation due to path loss and blockages,necessitating the use of directional antennas at both ends of the communications link. These are most likely to be implemented by means of an antenna array and beamformer in a highly integrated form within the RF transceiver. In such compact devices, antenna connectors are typically not available, thus negating the use of connective testing methodologies. Further, the mmWave operational environments synonymous with 5G New Radio (NR), are known to be highly dynamic in both spatial and temporal domains, hence the need for effective low cost mmWave Over-the-Air (OTA) testing for both product development, optimisation and compliance testing.The novel millimetre wave OTA architecture described herein, importantly facilitates the excitation of the Device Under Test (DUT) from multiple dynamic angles of illumination, thus representing realistic operating conditions for 5G NR, as well as the handover operation between multiple access points (APs). The method exploits the reflective properties of the ellipse, overcoming the pin-point focal regions by means of multiple discrete plane reflectors configured onan ellipsoidal frame. The evolved architecture offers a test zone commensurate with integrated mmWave antennas and beamformers as well as compliance with the testing specifications of the 3GPP standardisation body. The research presented is based on theoretical analysis and raytracing to develop the highly novel solution, culminating with a series of practical measurements.The technique developed offers a low-cost novel solution for testing devices operating at mmWaves frequencies (e.g. 28 GHz) with screen size of up to 7 inches (≈18 cm). The laboratory-based prototype offers multi-source excitation and a test zone volume of 20 cm by 20 cm by 20cm. The main advantage of this method is that the multiple signals illuminating the DUT can be generated from a single location by an individual two-dimensional (2D) phase antenna arrayconformed by multiple sub-arrays. To mimic real link conditions the feeder antenna must be connected to a base station emulator in order to stimulate the DUT with the test signals. Ifrequired, an optional channel emulator can create temporal, and frequency fading conditions.With a 2D array facet, it is possible to electronically beam steer the signals in both azimuth and elevation from the source point. The signals will be redirected by means of one or more reflectors towards the DUT, thereby creating a 3D spatially addressable stimulus. This architecture can be readily enhanced to improve the characteristics of the test zone through the use of specially shaped reflector, active reflectarrays or active metasurfaces.

Date of Award	21 Jan 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Mark A Beach (Supervisor) & Geoff Hilton (Supervisor)