CONCEPT OF
UAV-BASED ANTENNA MEASUREMENTS
UAV-based near-field probing allows sampling the electromagnetic near-field of an antenna in its very close vincinity and in unmatched large scan dimensions. At the same time UAV-based antenna measurement systems are extremely mobile and can be operated at nearly any spot in the world.
Tethered version of the HERCULES-ONE UAV during near-field probing of a wired standard gain horn antenna for 110 MHz from Technical University of Braunschweig / Institute for EMC (TUBS) at the Open Area Test Site of the Physikalisch Technische Bundesanstalt (PTB), being the German National Metrology Institute located also in Braunschweig. The measurement campaign was conducted in the frame of the NAVANT-NG project.
For extreme accurate determination of the positions of the measured NF-sample points, state-of-the-art laser metrology can be used. For the accuracte transmission of the RF-measurement signal between UAV and ground fibre-optic technology is used as well possibly in future also free-space laser technology might be used or even phaseless NF-FF transformation technologies.
However most important in the context of UAV-based near-field measurements is the need for an advanced near-field to far-field (NF-FF) transformation algorithm being able to efficiently and accurately transform irregularily and arbitrarily sampled near-fields into the antenna's far-field being of major interest for nearly all applications.
The need to use the advanced NF-FF transformation technology is based on the fact that UAVs can not fullfill the scanning requirements requested from the conventional FFT near-field far-field transformation asking for nearly ideal conical scan coutours with very equidistant distances between the sampled NF-points with an accuracy of app. 1/30 of the measured wavelength.
With considerable efforts over many years of intensive research an outstanding advanced NF-FF transformation algorithm was developped by the Chair of High-Frequency Engineering (HFT) of the Technical University of Munich (TUM) being an international acknowledged institue in the domain of computational electromagnetic field transformations.
Depending on the mission requirements the HERCULES-ONE platform can be operated in different configurations. Currently 2 types of UAVs are about to go into service. Details of the "HERCULES MICRO" and the "HERCULES-ONE" UAVs can be found in the table in the section "SPECIAL UAV MISSONS".
"HERCULES-ONE" Performances when using State-Of-The-Art RF-Instrumentation and Laser Trackers
| Scan Area Dimensions | Vertical planar: 300 m x 50 m (W x H) Cylindrical: 100 m x 50 m (∅ x H) |
| Frequency Range | 5 MHz to 20 GHz |
| Polarisations | Two orthogonal polarisations for linear and circular polarisations |
| Rx / Tx Mode | Covering transmitting and receiving DUTs |
| Dynamic Range | Better 80 dB in far-field |
| Pattern Accuracy | < ±3.0 dB @ -30 dB sidelobe level |
| Gain Accuracy | Better 0.5 dB |
| Data Collection | High-speed on-the-fly measurements, multi-frequency, multi-channel and multi-probe @ two orthogonal polarisations during one interleaved data collection / flight campaign |
| DUT Motions | None - "DUT motion-free" measurements |
