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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.

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.

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 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.

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.

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. >