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This project is aimed to study several transmit active array antenna concepts, both in Ku and Ka band, with the capability to address several missions with one competitive antenna in terms of performance and cost. The main technical challenge is to develop efficient reconfigurable antennas capable to support different high data-rate services at a cost that is proportionate to the market benefits and which makes them a viable alternative to reflector-based antennas.
The objectives of the activity are:
This activity is intended to develop a transmit array antenna concept that can penetrate the market as soon as possible, combining the most appropriate solutions to cope with the critical points of the DRAs (mass, volume, efficiency) and identifying a roadmap for the critical elements or promising technologies.
A Ku and Ka band transmit array antenna has been preliminary designed, based on fully commercially available technologies, following a generic and modular approach in order to minimise the recurring cost and reduce the time to market. As well, several technologies which will provide an added value to the proposed concept have been identified and a development plan proposed.
As conclusion of the activity, the proposed antenna concepts is ready to explode those niche markets which demand the fully flexibility that this antennas provides in terms of power allocation, shaping coverages and in-orbit reconfigurability, which makes them capable of affording some changes in the mission scenario during the lifetime, such as a different orbital position or a new coverage to be explode.
After a first proposal of 4 Ka missions, a secondary New Market mission was selected in order to show the capabilities of a Ka band DRA antenna. A preliminary design of the array concept based on a classical BFN was carried out. The proposed architecture allows handling up to 11 simultaneous spot beams with the required EIRP over any direction of the target zone, North Africa, from any of the possible orbital positions of the mission. The array is modular, composed of 432 horns arranged in hexagonal lattice, with a total aperture of 1 meter diameter.
Fig 1. Antenna top floor accommodation
Fig 2. Antenna basic RF module
The architecture is able to provide the required RF performances with a DC consumption and a thermal dissipation which fit within the scope of the defined mission with currently commercially available components. The antenna has a one meter diameter aperture and it is capable to handle 11 simultaneous beams, able to scan over any direction of the visible Earth with:
For this band, a primary telecommunication antenna was selected as the most promising mission to demonstrate the high capabilities of a DRA antenna. A transmit phased array has been designed for future telecommunication payloads. The array comprises 283 feed chains arranged within a circular aperture. Each feed chain consists on an amplifier, filter and radiating element. The amplifiers are based on GaN SSPA technology and the feed elements are linearly polarised horns with integrated filters. The manufacturing costs are reduced by manufacturing the feeds and filters in subarrays using additive layer manufacturing techniques. The assembly is modular, being built in strips which integrate structural support and integral heatpipes for thermal control (see figure below). The array radiates up to 430 watts of RF power distributed between 17 independent beams and has a power consumption of 2770W.
Fig 3. Strip module construction
The proposal for the ITT AO/1-5844/08/NL/CLP was sent in November 2008, and the Kick-off of the activity took place in March 2009.
During the first phase of the project, a survey of possible scenarios in which an array antenna would meet the market demand was done. This phase culminated in a Mission Requirement Review meeting in May 2009, in which the best mission scenario was selected.
This was followed by a study of different antenna concepts to fulfill the mission requirements, which culminated in a Concept Selection Review in November 2009.
The detailed design of the selected concept was done along the third phase of the project, which ended with the Baseline Design Review in September 2010.
Several mission scenarios in which a DRA antenna could solve the market necessities have been identified.
An assessment of different array antenna concepts capable to provide the required performances of the selected mission has been carried out.
The detailed design of the most promising array antenna concept both for Ka and Ku band has been done. The selected concept is based on technologies currently available; nevertheless, a roadmap identifying the activities needed to be pursued to improve the proposed concept has been elaborated. Within the possible improvements, the optical technology to implement the beam forming networks and the GaN technology for the SSPAs are the most remarkable.