There are technical challenges associated with testing 5G subscriber devices, too. The active antenna systems needed to ensure efficient beamforming for operation at mm-wave frequencies require highly integrated PCBs comprising antennas, amplifiers and analog phase shifters to keep internal attenuation low and circuit dimensions small. RF connectors for traditional conducted measurements are not available, so testing has to be done Over the Air (OTA). With OTA the distance between the DUT and the antenna of the measurement system needs to be considered. This distance is linked to the so called Fraunhofer distance describing the boundary between near field and far field. In far field the wave propagation can be described as plane wave and all measurements like modulation quality, transmit power and receiver sensitivity can be performed. The far field distance depends on the wavelength and the dimensions of the antenna aperture under test. At higher frequencies, the resulting larger distance would make far field analysis more difficult, particularly for FR1 tests that would require a very large test chamber, maybe 10 metres or more in length. New test techniques, and equipment such as Compact Antenna Test Range (CATR) solutions that are suitable for laboratory use, are emerging to overcome these challenges.
Another concern that arises during product testing is assessing the temperature sensitivity of the amplifiers and phase shifters used for beam forming and steering in the complex antenna array systems of 5G NR mm-Wave radios. Rapidly heating or cooling a large test chamber is impractical, so Rohde & Schwarz has developed a solution for isolating the environment around the DUT allowing the temperature to be varied without affecting the radiation parameters.
Test practices are also set to change significantly with the change to OTA testing. For example, tests must be performed in three dimensions to check for proper beam-forming operation, so a suitable 3D positioner must be used and the position of the unit under test recorded accurately in each case.