Modeling and design of a plasma-based transmit-array with beam scanning capabilities

Abstract This work presents the proof of concept of a novel plasma-based transmit-array antenna with beam scanning capabilities. The transmit-array operates above the GHz (precisely at 1.6 GHz) and is capable of steering its main lobe up to thirty degrees. A metallic half-wave dipole is used as the active element of the transmit-array, while twenty-five cylindrical plasma discharges are adopted to steer the beam of the antenna simply by turning them on or off. These passive elements are geometrically displaced in a triangular lattice. A customized two-steps optimization strategy is used to choose the best geometrical parameters of the array and to select the subset of plasma discharges that maximizes the gain of the antenna for each desired scanning angle. Towards this aim, a particle swarm optimization is first used to optimize the geometrical parameters of the array, and then a genetic algorithm is adopted to select the optimal subset of plasma discharges that need to be turned on to scan the beam towards different directions. The designed transmit-array was modeled in CST Microwave Studio, using realistic plasma parameters extrapolated from measurements of a fabricated plasma discharge prototype

Gauss-PSO algorithm for too short arc initial orbit determination for groud spot

The paper presents a new approach for the Initial Orbit Determination (IOD) from short observations of Resident Space Objects (RSOs). The work is in the framework of the development of the system SPOT promoted by the Italian Space Agency. The system SPOT (Star sensor image on-board Processing for orbiting Objects deTection) is composed by On-board SPOT, to detect potential RSOs from the on-board processing of star sensor images against the fixed stars, and the Ground SPOT which receives the observation data to perform the orbit determination and tracking of the RSOs. SPOT is a suitable system to detect small RSO (< 7 mm) that usually cannot be detected by ground-based observations. Due to the relative dynamics between the orbital observer and RSOs, an orbiting object appears as a streak in the star sensor image. As a result, the observation is a too short arc, which makes difficult to solve the initial orbit determination. The paper studies the IOD algorithm of Ground SPOT by devising a modified Gauss' Algorithm for space-based observer. Knowing the orbit of the observer, the measurements of the lines of sight of a RSO are used to find the state of the target orbit by the Particle Swarm Optimization (PSO) technique. The PSO is implemented in order to find the solution by minimizing a suitable cost function of the lines of sight. The developed algorithm it is able to provide a close estimate of the true state of the observer using too short arcs and it can autonomously choose a root of the Gauss' eighth grade equation

Star sensor image on-board processing for orbiting objects detection-spot

The increasing number of space activities has led to the growth of the population of Resident Space Objects (RSOs), i.e., satellites and space debris. The existing catalogues for RSOs are essentially based and updated by on-ground radars or optical measurements and their main limitation is related to the distance between the observer and the RSOs and the not continuous monitoring of the space segment. Such a limitation can be solved by using a network of space-based measurements. This work proposes the use of star sensors as RSOs detectors, taking advantage of their presence on many platforms. The status of the study conducted by the School of Aerospace Engineering of Sapienza University of Rome in the framework of the Italian Space Agency project SPOT (Star sensor image on-board Processing for Orbiting objects deTection) is described together with the architecture, design, state of development and preliminary results both for the on-board part of the system and the ground one. In the end, future developments will be presented and discussed

Stress competitivo e modificazioni cardiovascolari nell'ipertensione arteriosa essenziale Studio di un campione di dipendenti ENEA dell'area di Bologna

SIGLEITItal

L-band Plasma Turnstile Antenna for GPS applications

This work presents the preliminary results of a crossed dipole antenna that works in the L-band and that exploits plasma technology to generate and receive a circularly polarized electromagnetic field. The study considered in a first stage a simplified plasma crossed dipole and successively it included a more realistic design that comprises the plasma generation equipment, more realistic glass vessels and the electrodes used to generate the plasma. The simplified design can achieve good results in terms of axial ratio (i.e., circular polarization), directivity, and input impedance if compared to its metallic counterpart. However, when the more realistic antenna is considered, a down-shift in the operation frequency can be observed. Furthermore, the influence of the plasma parameters on the antenna parameters has been analyzed. All the results have been obtained through full-wave numerical simulations in CST Microwave Studio

The Alphasat Propagation Experiment: Interim Results from ASI and NASA Ground Stations

This contribution presents results obtained from the Italian ground stations in the frame of the Alphasat propagation experiment. Yearly statistics of the atmospheric attenuation as inferred from the received beacon signals (19.7 and 39.4 GHz) are reported and discussed for the two receiving stations installed in Spino d’Adda and Milan, whose experimental data are also combined to evaluate the advantage that would originate from a two-station diversity configuration

Endocrine and psychophysiological aspects of human adaptation to the extreme

Human beings need to adapt to any extreme, unknown, or isolated environment. This adaptation requires changes in the normal regulation of psychophysiological homeostasis, as described in terms of stress reaction. The aim of the present study was to monitor the processes of human adaptation to cold and isolated areas in Antarctica during the 12th expedition of the Italian National Research Program. Nine healthy subjects (experimental subjects), members of the expedition, and nine controls in Italy, were studied over a period of 2 months. Anterior pituitary hormone secretion, insulin, and melatonin, plus routine blood test, blood pressure, and ECG were performed. In addition, psychophysiological correlates were also recorded before and after the expedition period. In experimental subjects results of metabolic data suggested the presence of an increased peripheral insulin sensitivity at the end of the permanence in the station and a significant increased of total cholesterol. Hematocrite also significantly increased due to the conditions of hypobaric hypoxia. Results of endocrine data showed a significant decrease (p= 0.05) of hormone levels, which was associated with a significant decrement of the Galvanic Skin Response (GSR) activity to a standardized cognitive stress. No significant differences were reported in the controls. The data suggest that the exposure to the extreme environment develops a possible psychophysiological mechanism(s) that decreases the individual arousal

Design and numerical characterization of a realistic plasma dipole

This work presents the numerical results for a plasma dipole antenna that exploits plasma technology to generate and receive electromagnetic fields. Two models have been considered, namely an ideal plasma dipole, and a realistic plasma dipole. The latter comprises part of the plasma generation equipment (e.g. metal terminations, inductors). The realistic plasma dipole was realized in practice and tested for the plasma density. Moreover, a preliminary test by means of a vector network analyzer with the plasma turned off was undertaken to verify the accuracy of the simulation models. Both the models can achieve good antenna performances. However, a downshift in the operational frequency can be observed when a more realistic design is considered. All the simulated results have been obtained through full-wave numerical simulations in CST Microwave Studio