mm and sub-mm reflector system design ,
Antenna design ,
Automated test equipment ,
Quasi-Optical Network systems ,
Antenna testing ,
project managment
Publications (4)
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The Heterodyne Instrument for the Far-Infrared (HIFI) of the ESA cornerstone mission Herschel is required to operate at wavelengths between 157 and 625 μm. Because of the long-wavelength character, and the complexity and modularity of the optical design, there is a clear need for accurate electromagnetic simulations supported by experimental verification. The need for a compact layout in order to reduce mass and volume as far as possible has important optical consequences. Several mirrors are illuminated in the propagating near-field rather than in the far-field. Consequently the classical geometrical design and analysis approach is inadequate. The long-wavelength character of the system can not be ignored and the associated diffraction effects inevitably become important. In this paper we describe the results of electromagnetic simulations of the optical system for band 1 of HIFI at a wavelength of 625 μm. In order to verify the results of the front-to-end coherent propagation of the detector beams, near-field facilities capable of measuring both amplitude and phase of the electromagnetic field have been developed. A unique feature of these facilities is that the absolute coordinates of the measured field components are known within a fraction of a wavelength. Therefore a true comparison with theoretical predictions can be made. We compare measurement data taken at 625 μm with simulations and discuss to what extent measured and simulated results may be expected to agree. We conclude by presenting the consequences of our observations in terms of system performance.
This paper presents the key findings of an ESA-funded programme of work to investigate refractive systems and their application to precision polarimetry experiments. We briefly summarize the derivation of requirements on the optical system for CMB polarimetry, and the design of a refractive telescope system which meets these stringent requirements. An extensive programme of experimental work was undertaken in order to better understand the optical, thermal and mechanical characteristics of the lens material, and of lenses made from this material. A repeatable and controllable antireflection coating procedure was developed and validated, and used to coat lenses used in this study. Optical measurements before and after coating have been used to validate a new module for an industry-standard antenna modelling software package.
The Atacama Large Millimetre Array will be a single research instrument composed of up to 50 high precision antennas,
located at the Chajnantor plain in the district of San Pedro de Atacama, 5000m above sea level. Each ALMA telescope
will contain 10 frequency channels/bands, ranging from 30 to 950GHz. Radiation from the secondary reflector is
collected to the receivers of each wavelength channel through their accompanying front end optics. We present a full
electromagnetic treatment of the front end optics for band 5 (163 - 211 GHz) and band 9 (602 - 720 GHz). A full quasi
optical and physical optics analysis of the band 5 front end optics, using the antenna analysis tool, GRASP9 [1] is
presented. Potential optimisation for the system is presented, namely a reflector edge taper and a comparison of two
surface geometries. A similar analysis of the band 9 system is presented. Full electromagnetic simulations are compared
with cold beam pattern measurements made at the Space Research Organisation of the Netherlands [2, 3]. Analysis of the
effect of the polarizing grid is presented, with suggested modifications to improve cross polar levels.
KEYWORDS: Mirrors, Beam propagation method, Near field optics, Wave propagation, Telescopes, Near field, Radio propagation, Antennas, Black bodies, Scattering
HIFI is one of the three instruments for the Herschel Space Observatory, an ESA cornerstone mission. HIFI is a high resolution spectrometer operating at wavelengths between 157 and 625 μm. The need for a compact layout reducing the volume and mass as much as possible has important consequences for the optical design. Many mirrors are located in the near-field of the propagating beam. Especially in the long wavelength limit diffraction effects might therefore introduce significant amplitude and phase distortions. A classical geometrical optical approach is consequently inadequate. In this paper we present a rigorous quasi-optical analysis of the entire
optical system including the signal path, local oscillator path and onboard calibration source optical layout. In order to verify the results of the front-to-end coherent propagation of the detector beams, near-field measurement facilities capable of measuring both amplitude and phase have beam developed. A remarkable feature of these facilities is that the absolute coordinates of the measured field components are known to within fractions of a wavelength. Both measured and simulated fields can therefore compared directly since they are referenced to one single absolute position. We present a comparison of experimental data with software predictions obtained from the following packages: GRASP (Physical Optics Analysis) and GLAD (Plane Wave Decomposition).
We also present preliminary results for a method to correct for phase aberrations and optimize the mirror surfaces without changing the predesigned mechanical layout of the optical system.
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