Telecommunication
elham sharifi; Arash Ahmadi; Mohammad Fazaelifar
Abstract
The antenna of a high throughput satellite payload should generate multiple spot beams simultaneously to provide frequency reuse by creating cellular coverage for the satellite. The phased array antenna is a proper option for this application. In geostationary orbit, the satellite field of view is limited, ...
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The antenna of a high throughput satellite payload should generate multiple spot beams simultaneously to provide frequency reuse by creating cellular coverage for the satellite. The phased array antenna is a proper option for this application. In geostationary orbit, the satellite field of view is limited, and dividing it to several tight beams poses many challenges to the antenna design. The large dimensions of the radiating aperture, high number of radiant elements, the need for dividing the array into several sub-arrays, which lead to appearance of grating lobes, and the orthogonality of the beams with tiny angular distance from each other, are the challenges of the antenna design. In this article, a multiple beam phased array antenna in Ka-band with microwave beam forming network has been synthesized and designed to meet aforementioned challenges. The sub-beam technique has been used for decreasing the array dimensions. For eliminating the grating lobes, the array has been divided into interleaved sub-arrays in two dimensions. A new beam forming network has been designed in this paper which can generate several simultaneous orthogonal beams for interleaved sub-arrays
Telecommunication
Arda Afzali; Bahman Ghorbani Vaghei
Abstract
Finding the best possible scheduling to maximize observations and transfer them to the ground station as a function of satellite characteristics, orbital mechanics, attitude control system, field of view and observational objectives, is very important. The combination of the agility of the satellite ...
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Finding the best possible scheduling to maximize observations and transfer them to the ground station as a function of satellite characteristics, orbital mechanics, attitude control system, field of view and observational objectives, is very important. The combination of the agility of the satellite with regard to the ability to quick maneuver along the three axes of roll, pitch and yaw, with a suitable software can significantly improve the response rate, revisit time and satellite coverage and respond to users’ needs. In this regard, the design of a comprehensive scheduling that automatically creates an optimal operational sequence for the maximum utilization of agile Earth observation satellites during a certain period of time in order to respond to the needs and priorities of the users and to satisfy the operational limitations of the satellites. Therefore, in this article, the design of an automatic software for scheduling Earth observation satellites is presented, which after receiving observational targets from the user and assigning observation priority to each task, the ability to implement and execute observation tasks is checked by the attitude control subsystem to satisfy the attitude maneuver limit around the roll and pitch axes and orbital mechanics subsystem to satisfy the target access time window limit. Then, by using discrete event supervisory control, constraints are applied to the transfer system to add specific features and requirements to the mission. With the help of an optimal search algorithm based on the Bellman-Ford method, the optimal program sequence for the maximum use of the satellite while meeting the operational limitations of the mission is obtained automatically. Finally, a remote sensing mission is simulated to demonstrate the planned verification
Telecommunication
Hossein Eskandari; Razieh Narimani; Elham Hosseini
Abstract
In this paper a waveguide antenna to create a saddle shaped pattern for remote sensing satellite applications has been introduced, and a method to excite a waveguide as feeding X-band antenna with the aim of achieving circular polarization has been presented. With the use of a circular microstrip probe, ...
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In this paper a waveguide antenna to create a saddle shaped pattern for remote sensing satellite applications has been introduced, and a method to excite a waveguide as feeding X-band antenna with the aim of achieving circular polarization has been presented. With the use of a circular microstrip probe, the mode inside the cylindrical waveguide is stimulated in such a way that the antenna has circular polarization with only one feeding input, and in addition, the input impedance of the antenna is fifty ohms. To achieve the saddle-shaped pattern, plus-shaped guides have been used. These guides are printed as microstrips on the Rogers 5880 substrate. The innovation of this article is in the simultaneous use of directional elements to create a saddle-shaped pattern and a circular probe to create circular polarization in order to design a suitable antenna for LEO remote sensing satellites. After simulation, the antenna was fabricated and tested. The test results show that the antenna has a real gain of more than 3 dBi at angles of θ = ±65. The axial ratio of the antenna is less than 3 dB in the working frequency for θ values between ±50, which shows that the antenna has a desired circular polarization in this θ angle range.
Telecommunication
Sahar Abdi; Morteza Cheheltanan
Abstract
In this paper, a wideband high-gain microstip patch array antenna for high resolution synthetic aperture radar applications is presented. The antenna operation frequency is in the X-band and the antenna structure is a four-layer configuration consisting of radiating patches, slots, coupling cavities, ...
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In this paper, a wideband high-gain microstip patch array antenna for high resolution synthetic aperture radar applications is presented. The antenna operation frequency is in the X-band and the antenna structure is a four-layer configuration consisting of radiating patches, slots, coupling cavities, and a corporate feeding network, which in turn is fed by a coaxial probe. The increased frequency bandwidth of the radiating patch is achieved by employing a square slot, which appears as a cavity for it, and improves the gain and impedance bandwidth of the antenna array by isolating the patch feeding slot and eliminating the mutual coupling effect. The whole antenna structure is fabricated by using a combination of the milling process and printed circuit technology. Measurement results show a relative gain bandwidth of more than 10%, in which the antenna gain is measured above 28.8 dBi over the frequency band of more than 1 GHz. Moreover, the relative impedance bandwidth of the antenna for VSWR>2 is more than 16%.
