Source: {"pile_set_name": "USPTO Backgrounds"}

Electronic equipment, such as mobile communication devices, is subject to various electronic tests after production. Such tests are generally necessary to ensure proper configuration, calibration and functionality of various elements of the devices under test (DUT). For testing purposes, specific testing devices are employed which simulate a testing environment under predefined testing conditions. For example, testing devices may employ one or more specific testing routines with predefined testing schedules. Those testing schedules regularly involve input of particular test signal sequences into the DUT and/or reception of responses to testing signals input to the DUT. Such responses may be evaluated for consistency, constancy, timeliness and other properties of an expected behaviour of the DUT.
With radio-frequency (RF) communications standards having been stablished for wireless communication systems, ways to characterize such wireless communication systems in various signal propagation environments have become desirable. Environments in which electromagnetic waves propagate are subject to multipath effects such as fading or inter-symbol interference which effects influence the quality of signal transmission. Specifically for Multiple-Input Multiple-Output (MIMO) systems with more than one transmission antenna and more than one reception antenna, it is highly desirable to be able to characterize wireless communication systems under realistic conditions, i.e. with testing being performed over-the-air (OTA).
Equipment manufacturers and operators would like to evaluate DUTs by means of standardized measurements performed in realistic environments. As such, the emulation of multipath propagation channels in a controlled environment representing conditions that are substantially equivalent to the real environments is necessary.
For example, document US 2016/0226601 A1 discloses concepts for testing transmitters and/or receivers of wireless communication systems used in conjunction with antenna arrays. Document WO 2010/139840 A1 discloses a testing method in which a simulated radio channel is shifted with respect to a plurality of antenna elements coupled with an emulator for communicating with a DUT by using different directions for the simulated radio channel in an anechoic chamber. Document U.S. Pat. No. 8,912,963 B2 discloses a test system for testing MIMO systems within a test chamber. Rumney, M.; Kong, H.; Jing, Y.: “Practical active antenna evaluation using the two-stage MIMO OTA measurement method”; 8th Europ. Conf. on Antennas and Propagation (EuCAP) 2014, pp. 3500-3503, discloses methods evaluating the performance of active antenna array systems (AAS) using the two-stage MIMO OTA measurement method.
It would be desirable to find solutions for testing mobile communication devices that improve the characterization process of active antenna those arrays in mobile communication devices.