Search

Large deployable antennas are one of the key components for advanced missions in the fields of telecom and earth observation. In the recent past, missions have taken on board large deployable reflector (LDR) up to 22 m of diameter and several missions have already planned embarking large reflectors, such as the 12 m of INMARSAT XL or BIOMASS. At the moment, no European LDR providers are available and the market is dominated by Northrop–Grumman and Harris. Consequently, the development of European large reflector technology is considered a key step to maintain commercial and strategic competitiveness (ESA Large Reflector Antenna Working Group Final Report, TEC-EEA/2010.595/CM, 2010). In this scenario, the ESA General Study Project RESTEO (REflector Synergy between Telecom and Earth Observation), starting from the identification of future missions needs, has identified the most promising reflector concepts based on European heritage/technology, able to cover the largest range of potential future missions for both telecom and earth observation. This paper summarizes the activities and findings of the RESTEO Study.

The paper presents the design and validation of a dual band feed system for the reflector antenna of the CoReH2O (Cold Regions Hydrology High-resolution Observatory) SAR instrument, investigated under ESA contract. The antenna is a dual linearly polarized single-offset reflector, illuminated by two side feed arrays operating in X and Ku band respectively. Each array comprises seven compact multimodal horns in quasi rectangular waveguide. The horns are sequentially excited, a couple at a time, for optimum antenna pattern synthesis and secondary beams overlap. Each horn is a multiple step rectangular waveguide structure that provides the proper modal content at aperture, very close to the benchmark patterns analytically synthesized by modal superimposition at feed apertures level. The RF design has been validated through a complete characterization by test of the feeding system, proceeding from the single feeding elements to a complete feeding system composed by 4+4 elements. The measured results showed very good agreement with predictions at each stage of the campaign. Measured pattern has been used as primary source in the antenna model and very good performance have been predicted on secondary beams.

In 2009, Astrium GmbH, RuagSpaceAB and ComDev Europe have been charged by ESA for a Ku-band antenna feed bread-board (B/B) activity. The scope of the activity is to establish sufficient technology readiness for the Ku-band part of the dual-band (X- and Ku-band) and dual-polarized CoReH2O (COld REgions Hydrology High-resolution Observatory) ScanSAR instrument. The low-cost feed system is proposed in this paper based on the multi-feed antenna (MFA) concept. The design, the simulated and measured performance are presented. The measurements of the prototype show very good matching with the simulations, which confirm high performance of the device and its ability of fast beam scan in elevation.

In this paper accurate material measurements at sub-millimetre wave frequencies performed with two different systems are compared. Transmission and reflection results of high quality samples measured with a quasi-optical open resonator and a quasi-optical free-space bench are presented. Based on the comparison between the two results, an accuracy assessment of the transmission set-up is performed.

A dual-polarized Ku-band feed cluster is currently bread-boarded by Astrium GmbH, Ruag Space AB and Com Dev Europe for the ESA. It is proposed to be part of the dual-band (X- and Ku-band) CoReH2O Synthetic Aperture Radar (SAR) instrument. The scope of the paper is to report on the design and the performance of the Ku-band feed cluster as an important part of it. It will be shown that the proposed feed cluster is best suited for CoReH2O. It allows for fast beam scanning in elevation and is characterized by easy manufacturability, low cost, low implementation effort, and high performance.

The paper presents the array-fed reflector antenna of the CoReH2O (Cold Regions Hydrology High-resolution Observatory) SAR instrument currently being investigated within Phase-A under ESA contract. The antenna is a dual linearly polarized single-offset reflector, illuminated by two side linear arrays operating in X and Ku band respectively. Each array comprises seven compact multimodal horns in quasi rectangular waveguide. These are sequentially excited, a couple at a time, for optimum antenna pattern synthesis and secondary beams overlap. Each horn is a multiple step rectangular waveguide structure that provides the right modal content at aperture, very close to the analytical patterns synthesized through benchmarks. The Ku band feed has been subjected to a pre-development activity aimed at validating the design. The measured results at feed level show good agreement with predictions. Measured pattern has been used as primary source in the antenna model and satisfactory performance have been predicted on radiated beams. The X band feed has been designed with the same electromagnetic model adopted for Ku band and all performances are predicted with the same accuracy. Further breadboarding activities are foreseen in X band, finalized to characterize a reduced dual band feed cluster and the relevant switching systems, taking into account the effect of mutual coupling between the two frequency bands.

A reflectarray antenna that provides a focused beam in Ka band has been designed, manufactured and tested. The antenna demonstrator has been made up using two layers of patches printed on Kapton, which are bonded to low-loss prepreg quartz materials. The effect of the manufacturing tolerance errors in the dimensions and dielectric properties of the materials have been evaluated. A good concordance is achieved between simulations and measurements after taking into account the deviation in dimensions and dielectric constant. The measured 18-cm antenna provides a gain better than 33 dB in a frequency band from 31 GHz to 34 GHz.

Planck is a scientific satellite that represents the next milestone in space-based research related to the cosmic microwave background, and in many other astrophysical fields. Planck was launched on 14 May of 2009 and is now operational. The uncertainty in the optical response of its detectors is a key factor allowing Planck to achieve its scientific objectives. More than a decade of analysis and measurements have gone into achieving the required performances. In this paper, we describe the main aspects of the Planck optics that are relevant to science, and the estimated in-flight performance, based on the knowledge available at the time of launch. We also briefly describe the impact of the major systematic effects of optical origin, and the concept of in-flight optical calibration. Detailed discussions of related areas are provided in accompanying papers.

JIVE -Joint Institute for Very Long Baseline Interferometry (VLBI) in Europe -has managed under ESA contract the VLBI data acquisition of a stabile carrier-signal from Huygens' probe during landing on Titan in January 2004, using ~17 radio telescopes. Evaluation and investigation of the data is included in the same ESA contract. The scenario was described in a previous ICATT Conference (van 't Klooster, 2005). This presentation provides some published information of Huygens descent-trajectory as derived by JIVE. VLBI can be used for special radio-physical investigations, accurate Doppler information is a by-product. VLBI is applied now and in space-missions to come: probes, landers or spacecrafts for navigational, scientific or even telemetry tasks.

This paper presents the development and the ultimate results of the qualification activities of the 12 m unfurlable reflector assembly of the large deployable antenna (LDA), jointly developed by the Prime Contractor: g on a European technology. The paper also dedicates a section to a flight experiment (FE), which is a follow on activity of the LDA qualification, for the in orbit verification of the LDA performance. The final section of the paper provides an overview of the LDA possible applications at system level.

The reflectivity (reflection losses) investigations of high reflective metals like silver, copper, gold and real alloys at 100-200 GHz for applications in high sensitive satellite antennas and for high-power transmission lines and mirrors were made. The roughness values and the mechanical and galvanic surface treatment method are also presented.

The paper describes an example of spin-off of an advanced space technology development for application in an other high tech terrestrial field, namely for sub-millimetre radio telescope antennas

The Huygens Probe landed 14 January 2005 on Titan, the largest moon of Saturn. During and after the landing, Huygens transmitted data to Cassini, which acted as data relay station flying nearby Titan. There were two transmission channels. One of the two channels was very stable in frequency: it was locked to an on-board ultra stable oscillator (USO). Reception of its carrier signal of this transmission from Huygens has been possible with Earth-based radio telescopes at 1,200,000,000 kilometre distance. Frequency stability permitted to process signals received at different radio telescopes with very long baseline interferometry (VLBI) techniques. Exploitation of the latter techniques permits to retrieve the Huygens trajectory through the Titan atmosphere and actual landing location with superb resolution. The scenario for the VLBI experiment is outlined, the direct signal reception at two large radio telescopes is indicated and related descriptive information is given. Post-processing of VLBI data is ongoing at the time of writing in Joint Institute for VLBI in Europe (JIVE). Good progress can be indicated.

The paper describes how an activity is going on for a design, development and realisation of a large 12 meter deployable reflector antenna For space applications. The reflector antenna system is subject of an ESA contract awarded to Alenia Spazio as a prime contractor. The Russian company NPO EGS is responsible as sub-contractor for an important element, which is the deployable reflector. Alenia has provided, together with ESA, instrumentation and testing expertises for assessment of Passive Intermodulation properties of the realised reflector, which is currently being prepared for environmental testing. Background knowledge was fed into the program from the Georgian antenna design, comparable to the one, which did fly on MIR station.

This paper outlines the development status of an L-band synthetic aperture radar (SAR) antenna demonstrator undertaken by an industrial consortium under contract to the European Space Agency (ESA). Its aim is to verify the technology and the satisfactory performance of the SAR active antenna in advance of the development of the full L-band SAR instrument

Reflectivity (reflection loss) investigations of nickel samples with different types of surface finish, with and without rhodium coating, have been carried out in the 110-200 GHz frequency range on an installation developed in the Applied Physics Institute of Russia. The reflectivity measurements of high quality silver coated and gold coated mirrors are also presented. The reflectivity (reflection loss) investigations of some carbon fibre samples with and without aluminium coating have been made. Results are interesting, in view of the anisotropy of the carbon fibre material.

The ALMA (Atacama large millimetre array) project aims at a realisation of a 64-element radiotelescope ground array with 12 m Cassegrain antennas as single receiving elements. The receivers will operate between 30 and 900 GHz, thus putting very stringent requirements on each separate element or 12 m Cassegrain antenna. National Radio-Astronomy Organisation, NRAO, (USA) and European Southern Observatory, ESO, (Europe) have collaborated to realise, in 2003, two prototype antennas (for details, see www.eso.org under Atacama project). Surface accuracy requirements are below 10 /spl mu/m rms. An interesting technology has been selected for the reflector panels in one prototype: electroforming. The technology applied for the antenna reflector panels comes as a spin-off from a dedicated space technology development carried out for the XMM X-ray satellite project (www.esa.int and search for XMM). The technological developments needed to arrive at such accurate reflector panels are described, together with results and related achievements.

Results are presented of investigations with a laboratory model of a reconformable reflector for mm and sub-mm applications. A configuration with 19 actuators to control the surface has been realised. Several configuration shapes have been evaluated to prove the concept, using an accurate 3D measurement machine by Media Lario. With a reconformable reflector as sub-reflector one can alleviate requirements for a main reflector in a dual reflector system, which otherwise would be very challenging and expensive for sub-mm applications. This is of interest for instance for radiometers, sounders or ground-based radio-telescopes. The technological implementation here makes use of an electroformed nickel shell that allows a deformation as needed at sub-MM wavelength. The subject has been reported previously but without realised results. Here we present the latest status, which confirms this interesting and promising approach.

We present the results of investigations in order to design wideband horn antennas both with respect to the return loss and the cross polarisation level. The work reported was intended to design a microwave source with less than 40 dB VSWR, less than -50 dB cross polarisation and low sidelobes over 20% bandwidth. Two analysis techniques may be used for the simulation of such antennas: the method of moment (MoM) based on solution of integral equations, and the scattering matrix technique. The results presented have been obtained using the MoM technique by means of 1D integral equations.

The paper describes investigations and use of a reconformable reflector. Implementation is discussed for millimetre and/or sub-millimetre wave antenna configurations. The perspectives of alleviating requirements for the high-accuracy main reflector, which can be very expensive, are of great interest. This is the case in particular for space applications, with stringent environmental constraints. Applications for radiometers, sounders or ground-based radio-telescopes are of interest. The technological implementation is based on a galvanic electroformed nickel shell as developed by Media-Lario, which permits deformation capabilities suitable for mm/sub-mm applications.

Ultra high accuracy was achieved by Media Lario in the realization of large grazing incidence mirrors for the XMM telescope by electroformed nickel technology. The development of this technique also to the manufacturing of reflector antennas operating at centimeter and millimeter wavelength, has been carried out, achieving a surface accuracy of the order of the microns. The electroforming Ni technology, due to the high repeatability of the process which allows for the mass production with reduced recurring costs, is therefore to be considered as a cost effective approach for the realization of reflector panels for large ground station antennas.

Satellites in an orbit at a low or medium altitude require wide-angle shaped-beam antennas to realize a data link in an optimum fashion. RYMSA (Spain) owns the patent on a small, lightweight antenna with such characteristics, which has been developed in part, with ESA funding. The antenna is based on a balanced combination of two elements, namely a horn and a bi-conical horn. An antenna has been optimized for use on-board the METOP satellites.

A triple-frequency feed for a proposed satellite mission is discussed. The realized feed combines good radiation characteristics with a good match to free space over a large bandwidth in each of the three frequency bands (around 1.6, 5 and 22 GHz). Use has been made of a coaxial matching network, realized using an analytical model. Overall performance parameters for the feed combined with a parabolic reflector are presented. >

The purpose of the present paper is to describe computational methods for the analysis of a realistic beam waveguide (BWG) at X-band, using physical optics (PO) and the geometrical theory of diffraction (GTD). The results presented illustrate that both PO and GTD are very useful tools for the analysis of even large and complicated reflector antenna systems. The agreement between the methods provides a good check of the validity of the results. Further, GTD gives the user an insight in the actual diffraction processes that are taking place, a feature which is very helpful during the design of the antenna system. The applicability of GTD has been demonstrated at X-band. Since GTD is a high frequency approximation it will be even more valid at Ka-band. This is an important conclusion because the computer time for PO increases with the frequency raised to the power of four and a PO calculation at Ka-band is therefore not practically feasible.

The Meteosat Second Generation (MSG) program concerns the launch and operation of three new satellites. The MSG continues meteorological services, which are currently provided by the very successful first generation of satellites (Meteosat Operational Program-MOP), operated by Eumetsat. The MSG expands on services offered by MPO by providing more frequently data in more observation bands, with higher resolution. A telecommunication system on-board the MSG satellite transmits measured data to the primary ground station and receives and re-transmits pre-processed images and meteorological data as received from the latter station. Meteorological data are collected from data collection platforms. The MSG satellite carries a search and rescue transponder. The antenna sub-system has been specifically designed for the telecommunication functions and permits appropriate data throughput with the satellite spinning at a rate of 100 revolutions per minute. The antenna sub-system for the MSG is described, after a short general description.

Antennas with a shaped pattern are attractive for Low Earth Orbiting (LEO) Satellites. The use of a strong shaping assists to maintain a nearly constant power density level on the ground during the passage of the satellite over the groundstation. A lightweight but very solid antenna has been developed by RYMSA (Spain) to provide such characteristics. The antenna exploits a balanced combination of a biconical horn antenna and a hybrid mode feed and its performances are a result of dedicated theoretical and experimental investigations. The antenna configuration as such is of interest for various applications. It has been selected as data downlink antenna for the polar orbiting satellites of the METOP program.

The authors present a calibration technique for improving the accuracy of the near-field measurement with a 2D modulated scattering array. It is explained how the nonuniform characteristics in amplitude and in phase of a 2D array can be corrected by using a separate assessment of the array with a plane wave illumination. The calibration file is obtained by measuring a reference electric field provided by the ESTEC compact antenna test range. A comparison of a near-field measurement of a pyramidal horn is shown before and after such calibration. >

An efficient code for the analysis of beam waveguides and multireflector antennas by PO (physical optics) integration is presented. In the ELAB PO-code, there is no restriction on the number of reflectors, each reflector can be numerically specified to any shape, and the reflectors may be plane or parts of ellipsoids, with elliptical contours. The code has been applied to analyze a beam waveguide with six reflectors. The computer time was 177 s on a CRAY supercomputer. A comparison is made with Gaussian multimode analysis. >

A major step in the computation required to transform a plane-polar near-field into the far-field is the Hankel transform. One of the simplest ways to circumvent numerical Hankel transform evaluations is the interpolation method which converts the polar grid to a rectangular grid. This method turns out to be the most efficient plane-polar near-field to far-field transformation method

Planar near-field measurements were carried out on a single panel of the engineering model (EM) of the Synthetic Aperture Radar (SAR) antenna of the European Remote Sensing satellite ERS-1. The radiation behaviour was determined before and after exposure of the panel to a number of thermal cycles in vacuum. Transformation of measured near-field data back to the aperture plane has been exploited for antenna diagnostics to study anomalies found in the aperture distribution.

A technique involving the use of a 2-D fast Fourier transform has been developed to evaluate the plane-polar near-field-to-far-field transformation. Because of the efficiency of the interpolation, which makes it possible to compute the field in any plane comprising the origin of the polar grid, a software package including probe correction has been written to perform both plane-polar and plane-rectangular near-field-to-far-field transformations. A highly directive antenna with rapidly varying near fields has been used to test the proposed method. >

The engineering model (EM) of the synthetic aperture radar (SAR) antenna for the European remote sensing satellite ERS-1 has been electrically tested on a dedicated planar near-field test facility. An outline description of both antenna and test facility is given. Radiation characteristics of the antenna are presented that show good electrical performances for the model antenna. >

An electrically small offset reflector antenna (operating at 5.3 GHz) with very low sidelobes is presented. The antenna is envisaged for use in a transportable earth-based transponder for calibration of the active microwave instrument (AMI, which includes a synthetic aperture radar and a windscatterometer) onboard the European remote sensing satellite ERS-1. Antenna requirements, design, and performance are discussed. It is pointed out that stringent requirements on accuracy have pushed the testing to its limits in the far-field range. >

This paper presents the development and the ultimate results of the qualification activities of the 12m unfurlable Reflector Assembly of the Large Deployable Antenna (LDA), jointly developed by the Prime Contractor: Alcatel Alenia Space Italia and several Partners, under an ESA contract. The qualification campaign will be finalized within September 2006, opening near term opportunities for space applications relying on a European technology.