Over-the-Air test method for 5G mmWave devices with beamforming capabilities

Ever since millimetre-wave (mmWave) frequencies were considered as one of the key enabling technologies for fifth generation (5G) mobile communications, due to the availability of spectrum to achieve high data rates, increasing attention has been drawn towards how to evaluate the radiated performance of future 5G mmWave devices. Existing over-the-air (OTA) test methods for legacy mobile communications systems below 6 GHz are not directly scalable to mmWave frequencies. Conformance testing of mmWave devices requires a radically different approach than used previously since all test must be performed in a radiated fashion due to lack of connectors. Further, the signals in the mmWave propagation channel have narrow beamwidth and exhibit dynamic behaviours. This means OTA test systems need to be capable to emulate such conditions. Test signals must illuminate the device under test from multiple angles of arrival simultaneously and vary their direction electronically. This paper presents a novel OTA test method that offers a compact solution for the creation of such test environments, offering an alternative to the multi probe anechoic chamber method used previously below 6 GHz. The new method exploits the reflective properties of concave surfaces to provide cost-effective emulation of real-life dynamic angles of arrival, typical of real-life environments.