communications
Jaafar Bazrafshan; Fatemeh Sadeghikia; Ali Karami Horestani; Mohamed Himdi
Articles in Press, Accepted Manuscript, Available Online from 25 September 2023
Abstract
This paper presents a novel approach for designing a reconfigurable and steerable antenna utilizing plasma dielectric slabs along the aperture of a pyramidal horn antenna. The antenna offers electronic control over both the radiation gain and the direction of the main beam. The proposed configuration ...
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This paper presents a novel approach for designing a reconfigurable and steerable antenna utilizing plasma dielectric slabs along the aperture of a pyramidal horn antenna. The antenna offers electronic control over both the radiation gain and the direction of the main beam. The proposed configuration consists of four plasma slabs aligned perpendicular to the horn aperture along the horn axis, complemented by four diagonally connected plasma slabs. Each plasma slab can be independently switched ON or OFF, enabling dynamic adjustment of the radiation gain and steering of the main beam. Numerical investigations demonstrate that toggling the plasma slabs or controlling the plasma frequency of these slabs allows for fine-grained control over the radiation gain and beam steering of the pyramidal horn antenna. The selection of appropriate dimensions and angles for the plasma slabs plays a crucial role in achieving the desired beam steering angle and radiation gain control. To validate the concept, the proposed antenna configuration is designed and numerically simulated at a frequency of 10 GHz. The results indicate that the radiation gain of the antenna can be significantly enhanced, reaching up to 6.5 dBi. Additionally, the main beam direction can be steered within a range of ±12 degrees.
communications
Pedram Hajipour; Hossein Eftekhari; Ali Kheirdoost; Hassan Yeganeh
Articles in Press, Accepted Manuscript, Available Online from 03 March 2024
Abstract
Satellite constellations include a set of similar satellites that are distributed in a specific orbital pattern to accomplish a common mission. Satellite constellations are commonly used to accomplish missions such as global telecommunications, global positioning, and remote sensing. In this article, ...
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Satellite constellations include a set of similar satellites that are distributed in a specific orbital pattern to accomplish a common mission. Satellite constellations are commonly used to accomplish missions such as global telecommunications, global positioning, and remote sensing. In this article, by using scientometric approach, the structure and scientific maps of the field of "satellite constellations" in the world, as well as two leading countries, including the United States and China, have been analyzed based on research documents published in this field. In addition, a comparison has been made between these two countries with the world. The research community includes all scientific documents in the field of "satellite constellations" that have been indexed in the "Scopus" database between 1969 and 2023 AD. Also, in this article, knowledge maps (thematic subfields) and international cooperation maps of countries have been drawn using Bibexcel and VOSViewer software.
communications
Peyman Mohammadi; Mehdi Alemi Rostami
Volume 17, Issue 1 , March 2024, , Pages 37-48
Abstract
One of the most important issues related to the power supply of TWTA lamps in satellites is to have low ripple, high efficiency, high reliability and optimal volume and weight,. In this article, the efficiency and reliability of high voltage DC/DC electronic-power converter is optimized for use in satellite ...
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One of the most important issues related to the power supply of TWTA lamps in satellites is to have low ripple, high efficiency, high reliability and optimal volume and weight,. In this article, the efficiency and reliability of high voltage DC/DC electronic-power converter is optimized for use in satellite and TWTA lamps. The goal of optimization using multi-objective genetic algorithm (NSGA-II) in this article is to minimize the objective function, which includes efficiency and reliability. Markov model is used to evaluate reliability, in which short-circuit and open-circuit errors are considered for circuit switches and diodes, and short-circuit errors are considered for passive circuit elements. for optimization, first, the input variables of the algorithm are determined as the input of the objective function, so that with the help of sensitivity analysis, the parameters that have low sensitivity and their changes do not have a major impact on the objective function are eliminated. parameters of NSGA-II algorithm, including the number of iterations, the number of populations, and the probability have been determined for the accurate calculation of circuit variables. the results section this method, in addition to maintaining high efficiency, with the optimal selection of elements, high reliability can be achieved .
communications
Javad Ranjbar; Mohammad Fathi
Volume 15, Issue 4 , December 2022, , Pages 71-88
Abstract
In this paper, in order to provide telecommunication coverage for a wide geographical area, the use of a network consisting of an LEO satellite and a Tethered-Balloon equipped with antenna pointing mechanism is proposed. The proposed telecommunication network is able to send the collected data to a mission ...
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In this paper, in order to provide telecommunication coverage for a wide geographical area, the use of a network consisting of an LEO satellite and a Tethered-Balloon equipped with antenna pointing mechanism is proposed. The proposed telecommunication network is able to send the collected data to a mission center outside the covered region and receive the required telecommands, while providing a telecommunication link between the users in the covered region. To control and point the antenna beams towards desired targets, an Adaptive Dynamic Surface Controller is designed. Determining the required operating modes, designing a mode management algorithm and extracting the appropriate reference trajectories for each operating mode are among the discussed issues in this paper. The Uniform Ultimate Boundary (UUB) stability of the closed-loop system is proved and the performance of the control system is studied by simulation. The proposed communication network and control system are able to provide wide telecommunication coverage in remote areas or emergency situations.
communications
Mohammad Fathi; Javad Ranjbar
Volume 15, Issue 2 , June 2022, , Pages 27-41
Abstract
In emergency situations, where there is no possibility of using terrestrial-based or space-based telecommunication platforms or when there is a need for providing telecommunication services in remote, rural or hilly areas which are faced with lacking telecommunication infrastructures, typically using ...
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In emergency situations, where there is no possibility of using terrestrial-based or space-based telecommunication platforms or when there is a need for providing telecommunication services in remote, rural or hilly areas which are faced with lacking telecommunication infrastructures, typically using tethered balloon-based telecommunication technology is the best choice. Despite all the advantages of using this technology, small and limited coverage area is the biggest drawback of using tethered balloon platforms. In this paper, using a tethered balloon equipped with antenna pointing mechanism is proposed in order to, extend their small coverage area to a large region, in addition to benefit from inherent tethered balloons technology advantages. In this regard, dynamic and kinematic modeling of the proposed antenna pointing mechanism is discussed. In this research, the kinematic model is validated using RoboAnalyzer software and Robotics MATLAB toolbox. Antenna pointing mechanism provides the rotation ability for the antenna in two Azimuth and Elevation directions which increased the coverage area dramatically.
