EBG enhanced feeds for the improvement of the aperture efficiency of reflector antennas

We describe the use of electromagnetic bandgap (EBG) super-layers to improve the shape of reflectors illumination function. Following an investigation of the leaky wave pole singularities of the EBG Green's function, the shape of the radiation patterns of small apertures in ground planes are optimized. The maximization of the reflector aperture efficiency can be obtained by properly tuning the super layers geometrical parameters. A prototype of such feed has been designed, manufactured and tested. The results indicate that the inclusion of the EBG, increases the aperture efficiency of the feed+reflector system to values higher than 80%, over a 10% bandwidth. These low profile feeds are compatible with printed circuit board and/or integrated technology

Properties of leaky waves supported by grounded dielectric super-layers and implications on the design of reflector feeds

The design strategy that uses dielectric super-layers with neighboring wave-guides closed in matched loads constitutes a worst case scenario as far as the performance enhancement is concerned and finds applicability in radiometric imaging arrays. On the other side the design strategy that uses dielectric super-layers with neighboring wave-guides closed in properly tuned reactive loads can be seen as best case scenario representative of a multi beam system for a telecommunication satellite with independent channels

Metop-GRAS in-orbit instrument performance

The GRAS instrument on the Metop-A satellite provides more than 600 radio occultation measurement profiles per day. The instrument is characterized by its wide antenna coverage, high signal-to-noise ratio and an ultra-stable clock reference. The conventional dual-frequency tracking of GPS signals is under dynamic atmosphere conditions complemented by open loop tracking with sampling of the signal at a 1 kHz rate, providing an unprecedented view of the signal spectral environment. This paper presents the instrument performance as derived from analysis of in-orbit measurement data. We show that the noise figure is low enough to enable mapping of external radio noise variations over the earth\u27s surface. An error propagation model is presented to relate instrument characteristics to bending angle performance. This model is also used to illustrate the relation between filter bandwidth, resolution and measurement noise. The Doppler model, guiding open loop measurements, is found to be accurate to better than 20 Hz with a possibility for improvement to 10 Hz. The high performance at low altitudes enables the presence of surface reflections at the -20-dB level to be identified in more than 50% of the occultations. The potential performance improvements for next generation receivers are discussed

A dual beam slotted waveguide array antenna for SAR applications

the paper describes the design process and test results of a dual beam array antenna model. The objective of this ESA funded program is to study the realization of dual beams in a waveguide slotted array of the ERS-1 SAR type (10 m*1 m). The experimental model is 1 m*1 m and comprises 24 slotted waveguides and a Blass matrix feed network. The synthesis and design of the array and Blass matrix is described. Calculated and measured results of the experimental model are presented. The key component in the Blass matrix is a crossguide coupler. The authors present a novel design of a crossguide coupler which makes it possible to realize very tight coupling. Het betreft een dual-beam antenne voor active remote sensing (synthetic aperture radar SAR). Het ontwerp en realisatie proces en de test resultaten worden globaal beschreven. Een experimenteel 1x1meter slotted waveguide array model met Blass distributie netwerk laat toe om twee nagenoeg orthogonale (onafhankelijke) antenne bundels te realiseren. Hiermee zou de SAR werking verbeterd kunnen worden door de betere coverage vanaf de satelliet, ongeveer een factor 2

Metop-GRAS in-orbit instrument performance

The GRAS instrument on the Metop-A satellite provides more than 600 radio occultation measurement profiles per day. The instrument is characterized by its wide antenna coverage, high signal-to-noise ratio and an ultra-stable clock reference. The conventional dual-frequency tracking of GPS signals is under dynamic atmosphere conditions complemented by open loop tracking with sampling of the signal at a 1 kHz rate, providing an unprecedented view of the signal spectral environment. This paper presents the instrument performance as derived from analysis of in-orbit measurement data. We show that the noise figure is low enough to enable mapping of external radio noise variations over the earth\u27s surface. An error propagation model is presented to relate instrument characteristics to bending angle performance. This model is also used to illustrate the relation between filter bandwidth, resolution and measurement noise. The Doppler model, guiding open loop measurements, is found to be accurate to better than 20 Hz with a possibility for improvement to 10 Hz. The high performance at low altitudes enables the presence of surface reflections at the -20-dB level to be identified in more than 50% of the occultations. The potential performance improvements for next generation receivers are discussed

Multiple beam slotted waveguide antenna for spaceborne synthetic aperture radar

Not available