Effect of Conductive Propellers on VHF UAV-based Antenna Measurements: Experimental Results

Professional Unmanned Aerial Vehicles (UAVs) are generally equipped with carbon fiber propellers. Their conductivity and significant size can potentially increase both noise and systematics of UAV-based antenna measurement systems operating in the VHF band. A set of alternative fiberglass propellers has been manufactured and tested. This paper present measured results on the signal stability achieved with both fiberglass and carbon-fiber propellers at 175 MHz

Measurement of the LOFAR-HBA beam patterns using an unmanned aerial vehicle in the near field

An unmanned aerial vehicle (UAV) is exploited to characterize in situ the high-band antennas (HBAs) of the low-frequency array (LOFAR) CS302 station located in Exloo, The Netherlands. The size of an HBA array is about 30 m. The Fraunhofer distance (a few kilometers) is not reachable in the frequency band (120 to 240 MHz) within the flight regulation limits. Therefore, far-field patterns cannot be directly measured. The UAV, equipped with an radio frequency synthesizer and a dipole antenna, flies in the near-field region of the considered array. Measurement of three different frequencies (124, 150, and 180 MHz) is efficiently made during the same UAV flight. The near-field focusing method is exploited to validate the far-field pattern of the array under test within an angular range around the beam axis. Such a technique avoids both the time consuming λ∕2 sampling of the aperture field and the further application of computationally heavy near-field to far-field transformations. The array beam is well reconstructed in the main lobe and first sidelobes within a 2D scan plane sampled with a radial raster. A further postprocessing technique is proposed and validated on a subarray of HBAs. It suggests efficient ways for the future characterization of regular aperture arrays for SKA-MID Phase 2

Design and Verification of a Q-Band Test Source for UAV-Based Radiation Pattern Measurements

In the last years, the unmanned aerial vehicles (UAVs) generated significant innovations in in situ antenna measurements. UAV-mounted test sources have been exploited to characterize the radiation pattern of receiving antennas and arrays for HF radars, radio telescopes in very high-frequency (VHF) band, and up to the X-band for radar characterization. A UAV test source operating in the Q-band has been recently developed within the large-scale polarization explorer (LSPE) project. It will be used for the in situ validation of a ground-based cluster of coherent polarimeters for cosmology observation. This article presents the payload solution that is actually applicable to general UAV-based radiation pattern measurements in the Q-band. It is based on a phase-locked loop synthesizer and an active multiplier coupled with a power detector to compensate for signal power drifts in postprocessing. Relevant system tests have been performed in both laboratory environment and operative conditions. The measured outdoor radiation patterns are in good agreement with both the anechoic chamber measurements and simulated data

high performance microwave waveguide devices produced by laser powder bed fusion process

Abstract Additive manufacturing technologies are currently envisaged to boost the development of a next generation of microwave devices intended for satellite telecommunications. Due to their excellent electromagnetic and mechanical properties, metal waveguide components are key building blocks of several radio frequency (RF) systems used in these applications. This article reports the perspectives deriving from the use of laser powder bed fusion (L-PBF) technology to the production of high-performance microwave waveguide devices. A robust design of filters has been implemented in several prototypes manufactured in AlSi10Mg alloy. The corresponding measured performance confirm the applicability of the L-PBF process to the intended application

UAV-Based Antenna Measurements: Improvement of the Test Source Frequency Behavior

Drone-based radiation pattern measurements require the knowledge of the whole test-source radiation pattern in order to reach the expected measurement accuracy. However, the radiation pattern of the onboard antenna can be highly distorted by the metal frame of the vehicle, particularly in the VHF and UHF bands, showing highly resonant behaviors. This paper presents a preliminary analysis aimed to highlight such behavior and adopt compatible solutions to minimize or avoid the pattern distortion in the frequency of interest

Test-Driven Design of an Active Dual-Polarized Log-Periodic Antenna for the Square Kilometre Array

An active dual-polarized Log-Periodic antenna has been designed to meet the requirements of the low-frequency (50 - 350 MHz) radio telescope of the Square Kilometre Array (SKA). The integration of antenna and low noise amplifier has been conceived in order to achieve a high degree of testability. This aspect has been found to be crucial to obtain a smooth frequency response compatible with the SKA science cases. The design has also been driven by other factors such as the large-volume production (more than 130 000 antennas will be built) and the environmental conditions of the harsh Australian desert. A specific verification approach based on both wideband radiometric spectral and spatial measurements in relevant laboratory and in-situ conditions has been developed. Electromagnetic analyses and experimental results exhibit a very good agreement. In December 2019, this antenna was part of the reference solution for the System Critical Design Review of the SKA

SKA-low prototypes deployed in Australia : synoptic of the UAV-based experimental results

As the Square Kilometre Array progresses toward the construction phase, the first prototypes of the low-frequency instrument were deployed in Australia. To support such a crucial phase, a measurement campaign took place in the Murchison Radio-astronomy Observatory area to validate the electromagnetic models of the arrays by characterizing the embedded element patterns and the array beams. This article shows the significant campaign results in a comprehensive and readable way. Such a synoptic visualization allows for a direct evaluation of the complete dataset.peer-reviewe

3D Printing of a Monolithic K/Ka-Band Dual-Circular Polarization Antenna-Feeding Network

In this paper, a Ka/K-band antenna-feeding network in dual-circular polarization is reported. The design of the system was carried out in view of its monolithic manufacturing through selective laser melting in AlSi10Mg alloy. As a proof-of-concept for satellite telecommunication multi-beam applications, the feeding network operates in the K band (19.25, 20.75) GHz and in the Ka band (27.0, 29.0) GHz. The system provides four rectangular-waveguide ports and a common dual-polarized circular-waveguide port to be connected to the feed horn. The prototype exhibits measured values of in-band return loss better than 28 dB and a port-to-port isolation better than 19 dB (in polarization) and 50 dB (in frequency). The cross-polar discrimination is higher than 20 dB. In this regard, an elliptical-waveguide line was specifically designed and manufactured to recover a value higher than 30 dB in both frequency bands. The line can be easily integrated in the feed horn to be connected to the feeding-network thanks the ease of customization provided by 3D printing. The insertion losses are lower than 0.5 and 0.2 dB in the K and Ka bands, respectively. The weight of the prototype is approximately 130 g