Communications in the millimeter-wave region gets more and more attractive due to the availability of higher bandwidths. 3GPP 5G New Radio (NR) allocates channels in the frequency range from 23 to 53 GHz and IEEE 802.11ay between 56 and 75 GHz. Friis’ transmission equation relates the received (Rx) to the transmitted (Tx) power and depends on the Tx and Rx antenna gains and the path loss. The path loss scales as the square of the wavelength, which needs to be compensated at higher frequencies by applying high gain antennas. A common method to increase the antenna gain is to apply antenna arrays consisting of individually controllable radiators. The calibration and defect detection of antenna arrays is an important topic during their fabrication (e.g. mobile backhaul antennas), or conformance testing of user equipment containing millimeter-wave antenna arrays.
This session will introduce a test setup that allows calculating equivalent electric or magnetic currents on an arbitrary Huygens surface. These currents are obtained by applying the fast irregular antenna field transformation algorithm (FIAFTA), which was developed by the Chair of High-Frequency Engineering of the Technical University of Munich, to sets of near-field (NF) data, which were gathered with an R&S WPTC distributed-axis antenna measurement system. In order to apply the algorithm for array calibration or defect detection, the utilized Huygens surface covers the whole antenna array close to its actual geometry.
In an experiment, a Huber&Suhner backhaul antenna is operated at 75 GHz and measured via probing over a sphere of 1.2 m radius. The device under test (DUT) comprises 1024 waveguide antennas fed from a fixed waveguide splitting network. The size (102x106x8 mm3) of the DUT leads to a Fraunhofer distance of approximately 46 m. By conducting the tests under different conditions, the utilized NF inverse-source solutions are demonstrated to enable accurate detection of small defects within the array as well as analysis of the array feeding network performance in both magnitude and phase. In a second part of the study, the applicability of NF transformation in a compact antenna test range (CATR) environment is investigated. A new approach is implemented in order to retrieve the apparent range length and perform accurate back-propagation to the DUT.