PAGE CONTENTS
Objectives
The objective of the ESA-funded RESKUE project is to design and implement a prototype of a novel antenna for a portable satellite user terminal for provision of high data rates via a GEO satellite in Ku-band. The satellite terminal has to be easy to transport without a vehicle and easy to deploy. The antenna design is novel in that it comprises fine electronic pointing capability by means the reconfigurability of PIN-diode controlled elementary cells on the main reflector of a reflectarray. To keep the design cost efficient a reconfigurable elementary cell with 1-bit phase resolution is adopted.
Bidirectional high data rate ad-hoc satellite links are needed in several security and emergency scenarios to exchange various data information in remote locations where other telecommunication infrastructures may be either not available or inadequate.
Antenna apertures based on flat active reflectarray panels may allow the realization of large high gain deployable antennas with beam agility at this frequency band. By employing simple deployment mechanisms, reflectarray antennas composed of flat panels can be folded in a compact way and rapidly installed in a given location.
A certain level of beam agility eases the pointing of the antenna, allowing the user to only roughly align the antenna towards the satellite and then leaving the reflectarray antenna to perform the fine pointing in an automatic way.
The objective of the activity is to design, manufacture and test a portable and deployable transmit/receive Ku-band antenna composed of small flat active reflectarray panels. The antenna shall include a limited beam steering functionality and support self pointing once integrated with the transceiver.
When compared to existing systems, designed reflectarray antenna shall exhibit a reduced cost, a limited folded volume and an easy deployment while providing comparable radiofrequency performances.
Challenges
The ResKue project reflectarray shows a lot of challenging aspects. In order to obtain a full electronic reconfigurability of a reflectarray of these dimensions is necessary to find state-of-the art solutions able to allow at the same time an easy control of the reconfigurable devices and a low power consumption.
The specifications of the project moreover impose a very large relative bandwidth (more than 40%) in order to cover both the TX and RX bandwidth necessary for a bidirectional satellite link. The antenna must be operative also for both the possible linear polarizations. Considering all these aspect together the ResKue project represent a potenital brakthrough for the advances of the satellite systems.
Plan
The project plan starts with a review of the state of the art technologies related to the field of transportable transmit/receive antennas and with an identification of the most suitable architectures.
Two of them were selected for an RF preliminary design and optimization. Proposed reflectarray architectures were then compared in a review meeting in order to select the most suited to the project objectives.
According to the selected structure (shown in the previous sections) the RF design of the antenna has been carried out as well as the control circuit and the mechanical design. The RF design involve the project of PIN-diode based reconfigurable elementary cells, the sub-reflector, the feed and the dimensioning of the geometry of the antenna necessary to accomplish the requirements. The control circuit has been designed in order to drive all the elementary cells on the main reflector with a binary stream generated by a micro-controller integrated in the structure. The mechanical design focused on the need of a deployable and light structure easy to transport.
The results of all these activities converged in the prototype shown in the following figure (antenna during the measurements).
Results of the measurements validated the principle of operation of the antenna. The antenna properly reconfigured is able to point the radiation pattern in the desired direction and scan the beam both in azimuth and elevation in a wide scanning range as shown by the next figure.
Current Status
The project is currently closed. A wideband dual-polarization TX-RX reconfigurable reflectarray for emergency satellite communications in Ku-band has been developed within RESKUE project. The results of all the activities carried out resulted in a prototype of a full-reconfigurable reflectarray whose performance has been experimentally evaluated in anechoic chamber.
The results obtained validate the principle of operation of the design adopted: the antenna is able to completely reconfigure its main reflector in order to scan the main lobe in the desired direction with a very good accuracy. The results show that the state-of-the-art antenna proposed could open the road for systems able to innovate modern satellite communications.