K. van't Klooster

Novel Isoflux Antenna Alternative for LEO Satellites Downlink

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.

Large deployable antenna for various space applications

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.

Results of reflection loss measurements of sample material for radio astronomy telescope antenna for Planck Project

Advanced radio telescope antennas for space applications are realised by the use of stable composite materials, which are lighter in general than various metal realisations. Reflectivity measurements have been carried out on high technology samples for the Planck radio telescope. Highly accurate results have been obtained at the Applied Physics Institute in Nizhny Novgorod, and an independent measurement with a totally different setup at the University of Stuttgart confirmed that one of the samples showed a strange behaviour. Moreover, it confirmed the high accuracy of the testing method.

Modulated scattering techniques calibration procedure for a 2D array

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.<<ETX>>

Radiation Characteristics of a SAR Antenna Panel of ERS-1 Determined from Planar Near-Field Measurements

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.

17 radio telescopes observing the Huygens signal coming from 1,200,000,000 kilometer distance

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.

Radio astronomical phased arrays with fiber-optic design architecture

Fiber optics and microwave photonics are considered to be the technological basis for the solution of at least the two main design problems in large radio astronomical active phased arrays (RAAPA): phase stabilized LO reference signal transmission to each antenna element or subarray; antenna array beamforming. We describe in detail the solution to the former problem. It is the experimental version of a new fiber-optic link, operating in the remote heterodyning mode, with phase stability (<1/spl deg/ of phase) and full compensation of the insertion loss in the RF, microwave and millimeter wave frequency regions. Two principal methods of fiber-optic beamforming in a big RAAPA are also described in detail. The first one is based on an optical true-time delay (TTD) technique to realize the classic beamforming strategy by optical means. Systems of the second kind actively use hybrid coherent optical processors, replacing the classic beamforming strategy by holographic principles and avoiding the necessity of microwave radiation delay or phase shift evaluation in every array radiator in the real-time domain.

SOPERA: a new antenna concept for low Earth orbit satellites

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.

Design and validation of a X/ Ku band feed system for ScanSAR antenna

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.

Design and characterization of the CoReH2O Ku-band multi-feed antenna

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.