1,721,047 research outputs found
Characteristic modes analysis of mutually coupled log-periodic dipole antennas
No full textCharacteristic Modes Analysis (CMA) is a widely used method with recent progress in multi-antenna systems. We employ this method to characterize the mutual coupling phenomenon between two SKALA4.1 antennas, the low-frequency array elements of the future radiotelescope Square Kilometer Array (SKA-Low). The CMA accuracy is first validated at the lowest frequency range of interest with respect to a standard Method of Moments (MoM) solution by decomposing the single antenna into its characteristic modes. We then examine critical frequencies of a two-antenna system in modal decomposition, and characterize those responsible for the radiated electric field spurious spectral features owing to the mutual coupling. We connect these modes to first-order coupling of single antenna CMA modes, by using the eigenvalue data of both single- and two-antenna simulations
Dielectric Contrast Assessment for Skin Cancer Detection in the Terahertz Band
Full text linkIn the field of biomedical imaging, Terahertz waves offer significant advantages, such as non-ionizing radiation, excellent spatial and temporal resolution, and compact instrumentation size. Although the high absorption of water at these frequencies limits the penetration into biological tissues, it also serves as a source of contrast between healthy and pathological states, as the latter typically exhibit increased vascularization and, consequently, higher water content.
This study addresses the current landscape in which, despite the clinical application of Terahertz waves being far from routine practice due to unresolved challenges, there is a significant focus on skin diseases. The goal of this work is to identify a measurable and distinguishable contrast between healthy and pathological states, in the frequency band 0.4-1.6 THz, using dielectric property measures of healthy skin and basal cell carcinoma, along with an analytical model grounded in transmission line theory
Array Elements for LEO SatCom Payloads
Full text linkWith each generation of mobile communications, there is an exponential demand for both data transmission and a larger coverage footprint. One of the proposed solutions to these needs may be the deployment of communications via low orbit satellites, LEO SatCom. For this purpose, different types of antennas have been reviewed, such as waveguide-based aperture and All-Metal Vivaldi antenna
INVERSE RELATIONSHIP BETWEEN CHOROIDAL THICKNESS AND SUBCLINICAL RENAL DAMAGE IN ESSENTIAL HYPERTENSION
No full textThe introduction in last years of advanced techniques of optical coherence
tomography (OCT) has greatly increased our understanding of the choroid, that is
the most important vascular layer of the eye. Our study was aimed to assess
choroidal thickness by using Swept-Source OCT (SS-OCT) in essential hypertensive
patients (EHs) with and without subclinical renal damage (SRD).
We enrolled 100 EHs of which 65 without kidney damage and 35 with SRD. In all the
participants SS-OCT and a routine biochemical workup were performed. Glomerular
filtration rate (GFR) was estimated by the CKD-EPI equation (eGFR). SRD was
defined, by the presence of microalbuminuria or eGFR between 30 and 60
mL/min/1.73 m2. OCT measurements were performed according to the Early
Treatment Diabetic Retinopathy Study (ETDRS) protocol, that divides the macula into
9 subfields. The circular grid consists of 3 concentric rings.
EHs with SRD showed thinner choroidal thicknesses than those without kidney
damage (all p < 0.05), even after adjustment for age. Overall choroidal thickness
correlated significantly and directly with eGFR (r = 0.36) and negatively with urinary
albumin excretion (r = – 0.39). The association of choroidal thickness with SRD was
confirmed in multiple logistic regression analyses once the effect of age, antihypertensive
therapy and triglycerides was accounted for. The odds ratio of having
SRD associated with a standard deviation increase of overall choroidal thickness was
0.43 (0.24–0.75, 95% confidence interval; p = 0.007).
In conclusion, our study confirms the close relationships between changes in ocular
microcirculation and renal dysfunction
Platelet Orthomode Transducer for Q -Band Correlation Polarimeter Clusters
No full textThis paper presents a Q-band orthomode transducer (OMT) that has been designed according to the mechanical constraints of the platelet (multi-layer) manufacturing strategy. It is composed of a twofold symmetric coupling section with two electrically identical recombination networks. The two OMT outputs lay on the same plane to provide a suitable interface to the correlation unit. The two channels are equalized in both magnitude and phase according to the correlation polarimeter requirements. They also exhibit a very low cross-coupling (-50 dB) and good reflection levels (-28 dB) in the 21% bandwidth
Complex-Valued DNN for Broadband Dielectric Characterization of Dispersive Lossy Materials
Full text linkThis paper presents a broadband dielectric characterization method based on a Complex-Valued Deep Neural
Network (CVNN) that allows the retrieval of permittivity and
conductivity of dispersive lossy materials using ad-hoc setups. To
validate the method, we numerically tested it employing a partially filled custom-made double-ridge waveguide setup, working
from 0.95 to 4.2 GHz. Moreover, we include a feature importance
analysis using agnostic explainable-AI (XAI) techniques. The
results demonstrate the flexibility and the retrieval capabilities
of the method, as well as the advantages and drawbacks in
comparison with traditional techniques. We publicly release the
dataset and codes to support further research
Electromagnetics-Aware Path for UAV-Based Near-Field Antenna Measurements Implemented With a High Dynamic Range SDR
Full text linkAn electromagnetics-aware path for drone-based near-field (NF) antenna measurements is implemented in an outdoor experimentation. This technique allows us to significantly reduce the scan duration with respect to a standard half-wavelength NF scanning, using knowledge of the antenna under test (AUT) electrical size only. The validity of our approach is corroborated with planar outdoor NF measurements performed with an untethered drone transmitting at 750 MHz. To deal with the absence of phase coherence, the phase information is retrieved from a reference antenna, while a software-defined radio (SDR) having four super-heterodyne receiving channels is used to properly sample the high-dynamic signals resulting from the large scanning surface
Multi-Beam Arrays for Future LEO SatCom Payloads
Full text linkLEO satellite antennas must provide several beams at the same time up to Ka-band over a large scanning angle (up to ±60°). For this reason, high performance radiating elements and beamforming circuitry becomes crucial for the development of new constellations. This paper outlines the challenges and limitations of both waveguide-based and Vivaldi-based solutions and their impact on the beam-formed patterns
UAV-based measurement of sharp spectral resonances in mutually coupled SKA-low elements
Full text linkStrong mutual coupling between antennas can have detrimental effects in very sensitive radio telescopes based on aperture arrays. For the low-frequency instrument of the square kilometer array, narrowband perturbations in the radiation patterns of the inner elements have been predicted through electromagnetic simulations. This phenomenon deteriorates the spectral smoothness properties and disturbs the station calibration at very specific frequencies. In this letter, we present a new unmanned aerial vehicle (UAV)-based methodology to experimentally characterize such narrowband phenomena with a high-frequency resolution by means of independently-sweeping transmitting and receiving equipment. This solution does not add complexity to the system (e.g., by tethering the UAV). Results and predictions are in good agreement confirming both the presence of spurious resonances and the validity of the simulation approach
Skew Incidence Plane-Wave Scattering From 2-D Dielectric Periodic Structures: Analysis by the Mortar-Element Method
Full text linkA 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
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