  Cellular-connected unmanned aerial vehicles (UAVs) have recently attracted a
surge of interest in both academia and industry. Understanding the
air-to-ground (A2G) propagation channels is essential to enable reliable and/or
high-throughput communications for UAVs and protect the ground user equipments
(UEs). In this contribution, a recently conducted measurement campaign for the
A2G channels is introduced. A uniform circular array (UCA) with 16 antenna
elements was employed to collect the downlink signals of two different Long
Term Evolution (LTE) networks, at the heights of 0-40m in three different,
namely rural, urban and industrial scenarios. The channel impulse responses
(CIRs) have been extracted from the received data, and the spatial/angular
parameters of the multipath components in individual channels were estimated
according to a high-resolution-parameter estimation (HRPE) principle. Based on
the HRPE results, clusters of multipath components were further identified.
Finally, comprehensive spatial channel characteristics were investigated in the
composite and cluster levels at different heights in the three scenarios.
