RF measurements in a 5G world

While many IT and networking experts may consider the physical layer of a wireless network as nothing more than a major inconvenience like a bad Ethernet cable, there's an incredible amount of complexity to the operation of a single radio and to being able to make a wireless link between two radios. Most of the tests needed to qualify the functionality of a radio are traditionally done in a conducted environment using an RF cable, with only the final transmitter and receiver radiated performance of the fully integrated device having to be evaluated through the antenna. However new technologies being incorporated into the 5G New Radio will make that process impractical if not completely impossible. For 5G, high gain beamforming arrays will be used to direct a given signal to a specific user thereby increasing the network density by allowing multiple users in the same space without causing mutual interference. By directing the energy for a signal to the targeted user rather than broadcasting it to everyone on the network, power requirements are significantly reduced as well. So although these 5G radios will be much more efficient both in spectrum and power usage, they do so at a cost of complexity in design. These beamforming phased arrays replace a single antenna with tens or hundreds of antenna elements, each with their own associated RF circuitry. Even if one wanted to test each path separately, the physical constraints make adding connectors to each antenna element impractical at best, and impossible at the higher frequencies where the physical size and spacing of the elements shrink to a few millimeters. More importantly, since the net performance experienced by the user occurs in the main beam of the antenna after the power from each element is combined over the air, most of the desired operational and performance criteria can only be evaluated in a radiated over-the-air test. In addition, the added functionality of the beamformer itself, including its ability to track a target as a mobile device or other objects in the environment move, requires the development of new test requirements. This paper will cover these topics in detail and discuss the latest progress in the 3GPP 5G New Radio RF Test work item.