Over-the-Air testing

Abstract Ever since 4G, the role of MIMO antennas has become increasingly important in the increased sophistication of mobile communication systems. This has been and continues to be the subject of endless research, some of which has been incorporated into standards. However, the theoretical advantages of advanced antenna techniques are often just that, theoretical. This situation has been exacerbated by the migration to mmWave frequency bands in 5G which, as explained in this chapter, are unable to use the Over The Air (OTA) test systems developed for 4G. Consequently, many performance requirements remain unspecified and untested.. The study of the verification of MIMO radiated performance started in COST around 2008 in COST 2100, continued in COST IC1004 and featured again in COST IRACON. This chapter outlines some of the key technical challenges in emulating the complex 3D EM fields necessary to verify MIMO performance. Despite the apparent need for tests systems capable of proving the theory of MIMO systems, the activities of 3GPP have been muted in that key MIMO performance targets remain undefined several years after 5G was first specified. These include the new aspects of spatial dynamics which are essential to mmWave operation. Several new test methods are introduced including the sectored multi-probe anechoic chamber to overcome the challenges of large electrical device size, and the use of elliptical reflectors to generate the fields needed to test spatial dynamics.