For next generation SAR products, Thales Alenia Space Italy (TAS) has developed and qualified dual-polarization array antennas, based on slotted waveguides fully realized in aluminum technology. In large deployable active array implementations, the proposed solution offers significant advantages over other existing technologies, in terms of reduced ohmic losses, improved mechanical stiffness, thermal dissipation capabilities, manufacturing and assembly. A qualified dip-brazing technology is employed for manufacturing the slotted waveguide sub-array panels, achieving a compact envelope and reduced overall antenna mass. A radiating panel demonstrator has been manufactured and qualification tested, showing very good performances, in full agreement with design predictions.

This paper describes developments at Thales Alenia Space in Italy aimed at a next generation of products for spaceborne SAR active arrays at C, X and Ka band, based on GaN frontends.

The article presents the design of a Ka-band synthetic aperture radar (SAR) instrument based on innovative phased-array antennas, with steering capability in azimuth and elevation. To limit the complexity and costs associated with conventional large active arrays with regular layouts, a sparse array concept is presented. The proposed approach results in a 40% reduction in the number of active controls, with a marginal reduction in performance compared to conventional phasedarray solutions previously developed for SAR instruments. Additionally, a preliminary thermomechanical design is presented to assess the challenges associated with the industrial production and to identify options for accommodation on the spacecraft.

A novel sparse layout for the receiving aperture of a Ka-band spaceborne SAR has been designed. The devised array antenna layout allows reducing the number of active controls of 40%, from 10000 to 6000. The antenna is designed to steer the beam ±10° in elevation and ±2° in azimuth, and satisfies the prescribed pattern mask. In this paper, after briefly recalling the electromagnetic design of the antenna, the arrangement of the electronic layeris described in detail, together with the thermomechanical design and the aspects concerning the accommodation of this sparse SAR array antenna in the satellite bus.

The paper provides an overview of the most significant space antenna products and technologies for Observation, Exploration and Navigation (OEN) developed by ThalesAleniaSpace-Italia (TAS-I) over more than 30 years. These antennas provided a determinant contribution to the scientific community in understanding earth environment and solar planets. An outline of today key developments is also presented.

This paper focuses on the introduction of sparsity in a planar spaceborne SAR antenna array operating in Ka-band. Given the different requirements in azimuth and elevation, and the large size of the array, sparsity is introduced along the two dimensions separately. While sparsity along the azimuth dimension was considered in an earlier paper, the application of density tapering along the elevation dimension is described here and preliminary results are reported.

The design, manufacturing, and testing of a slot-coupled multilayer dual-polarized X-band radiating element is presented. The proposed architecture provides an isolation between polarization ports better than 34 dB over a 16% frequency band. The selected technology is particularly suitable for large-scale, low-cost, and high reliable manufacturing. This work has been carried out in the frame of a research program funded by the Italian Space Agency and aimed to the development of enabling technologies exploitable in next-generation spaceborne synthetic aperture radar (SAR) antennas.

The design, manufacturing and testing of a planar technology, fully integrated, multilayer, dual-polarized power distribution network, feeding a six element X-band linear array is presented. The selected technology, not used yet for space applications, is particularly suitable for large scale, low cost manufacturing. The proposed architecture provides an isolation between the two polarizations better than 40 dB, an input ports return loss better than 25 dB, and a 0.6 dB worst case amplitude unbalancing with a maximum phase shift of about 9 degrees between output ports, within a 16.7% bandwidth.

"COSMO - SkyMed di Seconda Generazione" (COSMO SG) is a programme funded by the Italian Ministry of Research and by the Italian Ministry of Defence (I-MoD), and conducted by the Italian Space Agency (ASI) with I-MoD at the aim of pursuing a twofold goal: assuring SAR data continuity to the users of "COSMO - SkyMed" (CSK) and enhancing the capability of that system in terms of functionalities and performance. In accordance with the mentioned objectives, COSMO SG will enable astonishing Earth observation capabilities, satisfying emerging needs of both civilian and military users. Within the frame of this programme, to comply to the applicable user's requirements, Thales Alenia Space Italia S.p.A is charged of developing an innovative multi-mode X-band Synthetic Aperture Radar (SAR), to confirm the image quality performance of CSK, to improve the resolution achievable by the system and to provide the novel capability of supporting acquisitions based on simultaneous dual polarisation on receive. This paper provides a description of the SAR instrument design, gives an outline of the key parameters of the instrument and describes the main enabling technologies developed in order to implement this design.

A brand-new design of the Synthetic Aperture Radar (SAR) instrument has been conceived, capable to make the space resolution of the "narrow field images" finer than COSMO-SkyMed First Generation satellites (CSK), while providing multi-polarization. The technologies necessary to sustain improved performances interest all SAR payload elements, realizing completely renewed design of SAR central electronics and active phased array antenna with respect to CSK. A renewed Payload Data Handling and Transmission (PDHT) design significantly improves the performances of the PDHT currently in use in CSK, in terms of on-board data storage capacity (doubled), space-to-ground data transmission throughput (doubled), data reception rate from SAR. The technology innovations relate to all composing elements of PDHT, such as on-board memory cells, command & control software, data encryption, modulation scheme, communication devices. The Satellite Platform has been enhanced with respect to CSK, in terms of augmented electrical power (necessary to cope with the increased peak power required by the payload), an Avionics Subsystem (AVS) new state-of-the-art design (enhanced sensors technology and a very high satellite agility), a new transponder with enhanced data rates and an increased propulsion fuel tank capacity for an extended operative lifetime. This paper describes the COSMO Second Generation challenging technologies and design put in place in the LEO SAR Satellites context.

An innovative three-step procedure for the synthesis of linear phased arrays with nonuniformly spaced elements is presented. The main objective is to obtain an array with a minimal number of elements and an optimal efficiency of the amplifiers driving the elements. The procedure consists of three steps. First of all, a periodic array with a single-amplitude tapering and as much phase tapering as there are required shaped patterns is derived. Then, starting from the results of the first step, an equiamplitude nonperiodic array, with a number of phase tapering equal to the number of required patterns and with a minimum number of radiators is synthesized. Finally, a numerical optimization permits refining the results so as to satisfy the design constraints.

The paper presents the design guidelines for Active SAR Antennas followed for the development of COSMO Sky Med SAR Antenna Subsystem. They have brought to define the antenna architecture, the RF, and electrical requirements for all the antenna RF, digital and power units, taking into account the available technologies and achievable performance. The antenna design is described for what the main subsystems is concerned, such as RF, power, digital, including mechanical and thermal aspects. Finally the paper reports also a brief description of the most recent development carried out in Canada and in Europe in the last ten years, including the on-going programs.

The authors present the design technique and the measured results of a planar circularly polarized microstrip patch array composed of 4/spl times/4 patches for space applications at S-band. A comparison of the two array configurations shows that the use of hybrid power splitters improves the return loss and the peak axial ratio but drastically reduces the antenna efficiency. The improved array configuration keeps high efficiency over a wide frequency band.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>