Skew Incidence Plane-Wave Scattering From 2-D Dielectric Periodic Structures: Analysis by the Mortar-Element Method

A full-wave simulator of 2-D dielectric periodic structures under skew plane wave incidence is presented in this paper. A differential formulation is used and the boundary value problem is solved by means of a multi-domain spectral method. Suitable mappings allow the efficient analysis of dielectric elements with rounded corner cross sections. A comparison with the results obtained by the method of moments and with a commercial simulator is presented for an array of dielectric rods and for a surface-relief diffraction grating

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

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

When Meta-Surfaces Meet Users: Optimization of Smart Radio Environments in 6G Sub-THz Communications

We consider a smart radio environment where meta-surfaces are employed to improve the performance of wireless networks working at sub-THz frequencies. To this end, we propose a comprehensive mathematical channel model, taking into account both the ability of the meta-surfaces to redirect the impinging signal towards a desired direction, and the signal reflection due to large objects. We show how the design of both the meta-surface and the transmitter precoder influences the network throughput. Furthermore, we compare several algorithms to optimize the effect of the meta-surfaces in a realistic scenario. As a result, a simpler algorithm that associates network users and meta-surfaces provides a performance comparable to more complex numerical optimization methods. Simulation results suggest how many users are supported in the designed system

UAV-aided calibration for commissioning of phased array radio telescopes

Calibration of antenna positions and instrumental response is a crucial step in the commissioning of a phased array radio telescope. The Low Frequency Aperture Array system of the Square Kilometre Array (SKA) is envisaged to consist of about 131,000 antennas. In this paper, we propose a strategy to efficiently conduct commissioning calibration of such a large phased array radio telescope using a near-field probe mounted on an nmanned Aerial Vehicle (UAV). We demonstrate the effectiveness of the proposed method using simulations. This indicates that potentially cost-saving relaxation of requirements on placement accuracy is possible. We also propose to validate this method in practice using the Low Frequency Array (LOFAR)

Life Fertility Tables of Piophila casei L. (Diptera: Piophilidae) Reared at Five Different Temperatures

Abstract Piophila casei L. or cheese skipper is a well-known fly with a controversial role: it is considered harmful in the food industries but important in nature as a detritivore and useful for studies in forensic entomology. The temperature response of P. casei was studied at five constant temperatures: 15, 19, 25, 28, and 32°C. The lowest mortality percentage of eggs was recorded at 15°C and the highest at 32°C. Conversely, less mortality was observed for maggots at higher temperatures. The developmental time from first instar to adult decreased with temperature reaching the lowest value at 32°C (13.7 d). Adult longevity was strongly affected by temperature, decreasing from 20.5 d at 15°C to 6.6 d at 32°C. Mean total fecundity per female was higher at 25°C and lower at 15 and 19°C, whereas the best performance in mean daily total fecundity per female was recorded at 32°C. Male longevity followed a similar trend to the one observed for females. The net reproductive rate (R0) was greatest at 25°C, where..

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

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

Additive Manufacturing of RF Waveguide Components

The exponential growth of publications, in the last years, on the use of additive manufacturing (AM) technologies in the microwave field proves the increasing interest of research institutions and industries in these techniques. Some advantages of AM with respect to conventional machining are weight reduction, design flexibility, and integration of different functionalities (electromagnetic, thermal, and structural) in a single part. This chapter presents the most employed AM technologies for the manufacturing of RF waveguide components. First, an overview of the AM processes is discussed with particular care on material properties and post-processing. Then, an extensive survey on microwave-guided components fabricated by AM processes published in literature is shown