Probing the Early Universe with the PLANCK Surveyor

Abstract included in text

Quasi-optical multiplexing using reflection phase gratings

Heterodyne array receiver systems for both ground based and satellite telescope facilities are now becoming feasible for imaging in the submillimetre/terahertz regions of the EM spectrum. Phase gratings can be usefully employed as high efficiency passive multiplexing devices in the local oscillator (LO) injection chain of such receivers, ensuring that each element of the array is adequately biased and that the reflected LO power level at the array is minimised. For the wavelengths of interest both transmission and reflection gratings can be manufactured by milling an appropriate pattern of slots into the surface(s) of a suitable material. Thus, the required phase modulation is produced by the resulting pattern of varying optical path lengths suffered by the incident wave-front. We report on work we are undertaking to develop all reflection quasi-optical multiplexing systems so as to reduce reflection losses at the grating and minimise the number of surfaces that can contribute to standing wave effects in the optical system. As part of this endeavour we have also developed a quasi-optical technique for analysing the inevitable degradation due to multiple reflections on transmission grating design. This analysis is based on the Gaussian beam mode technique, and a further application of this technique allows one to assess tolerance limitations on the grating

Determination of the Phase Centers of Millimeter-Wave Horn Antennas Using a Holographic Interference Technique

In this paper, we discuss how a holographic interference technique can be applied in the experimental determination of the phase centers of non-standard horn antennas in the millimeter-waveband. The phase center is the point inside the horn from which the radiation appears to emanate when viewed from the far-field, and knowing its location is necessary for optimizing coupling efficiencies to quasi-optical systems. For non-standard horn designs, and other feed structures, the phase center may be difficult to reliably predict by simulation, in which case, before committing to antenna manufacture, there is a requirement for it to be determined experimentally. Although the phase center can be recovered by direct phase measurement of the far-field beam pattern, this usually involves expensive instrumentation such as a vector network analyzer for millimeter wave horn antennas. In this paper, we describe one inexpensive alternative, which is based on measuring the interference pattern in intensity between the radiation from the horn of interest and a reference beam derived from the same coherent source in an off-axis holography setup. The accuracy of the approach is improved by comparison with the interference pattern of a well-understood standard horn (such as a corrugated conical horn) in the same experimental setup. We present an example of the technique applied to a profiled smooth-walled horn antenna, which has been especially designed for cosmic microwave background (CMB) polarization experiments

Quasi-optical phase retrieval of radiation patterns of non-standard horn antennas at millimetre and submillimetre wavelengths

The location of the phase centres of antenna feeds is critical for optimised sensitivity and resolution on reflector antennas and telescopes. While the measurement of the far-field intensity patterns of such feeds is relatively straightforward, the direct recovery of their phase patterns requires access to expensive phase sensitive instrumentation such as a vector network analyzer. We present an inexpensive alternative quasi-optical technique, analogous to off-axis holography at visible wavelengths, that allows for the phase curvature of the feed pattern, and thus the phase centre, to be recovered with sufficient accuracy for optimizing aperture efficiency and resolution on a reflector antenna. We discuss the accuracy of the technique and compare results for the case of a specialized horn antenna for CMB polarization operating at 100GHz, using both the quasi-optical method and a vector network analyzer as a bench mark measurement tool for verification of the approach. We also include some measurements made of a lens antenna fed by a bare waveguide radiator

Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the “Centro Astron´omico de Yebes” is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens

Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the “Centro Astron´omico de Yebes” is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens

Experimental Verification of Electromagnetic Simulations of a HIFI Mixer Sub-Assembly

Phase II of the study "Far-Infrared Optics Design & Verification", commissioned by the European Space Agency (ESA), we investigate the ability of several commercial software packages (GRASP, CODEV, GLAD and ASAP) to predict the performance of a representative example of a submillimeter-wave optical system. In this paper, we use the software packages to predict the behaviour of a Mixer Sub-Assembly (MSA) of HIFI, and we compare the simulations with near-field measurements at 480 GHz. In order to be able to distinguish between the predictions of the packages, we move the corrugated horn of the MSA through its nominal focus position. A unique feature of the experimental arrangement is that the measured position of every field point is known absolutely to within fractions of a wavelength. In this paper we present the results of this through-focus experiment, which give a good first-order indication of the agreement between measured and simulated behaviour of a typical submillimeter-wave optical system

Optical requirements and modelling of coupling devices for the SAFARI instrument on SPICA

The next generation of space missions targeting far-infrared bands will require large-format arrays of extremely low-noise detectors. The development of Transition Edge Sensors (TES) array technology seems to be a viable solution for future mm-wave to Far-Infrared (FIR) space applications where low noise and high sensitivity is required. In this paper we concentrate on a key element for a high sensitivity TES detector array, that of the optical coupling between the incoming electromagnetic field and the phonon system of the suspended membrane. An intermediate solution between free space coupling and a single moded horn is where over-moded light pipes are used to concentrate energy onto multi-moded absorbers. We present a comparison of modelling techniques to analyse the optical efficiency of such light pipes and their interaction with the front end optics and detector cavity

Multimode simulations of a wide Field of View double-fourier far-infrared spatio-spectral interferometer

In the absence of 50 m class space-based observatories, sub-arc-second astronomy spanning the full far-infrared wavelength range will require space-based long-baseline interferometry. The long baselines of up to 10’s of meteres are necessary to achieve sub arcsecond resolution demanded by the science goals. Also, practical observing times command a field of view toward an arc minute or so, not achievable with a single on-axis coherent detector. This paper is concerned with an application of an end-to-end instrument simulator PyFIInS, developed as part of the FISICA project under funding from the European Commission’s 7th Framework Programme for Research and Technological Development (FP7). Predicted results of wide field of view spatio-spectral interferometry through simulations of a long-baseline, double-Fourier, far-infrared interferometer concept are presented and analysed. It is shown how such an interferometer, illuminated by a multimode detector can recover a large field of view at sub-arcsecond angular resolution, resulting in similar image quality as that achieved by illuminating the system with an array of coherent detectors. Through careful analysis, the importance of accounting for the correct number of higher-order optical modes is demonstrated, as well as accounting for both orthogonal polarisations. Given that it is very difficult to manufacture waveguide and feed structures at sub-mm wavelengths, the larger multimode design is recommended over the array of smaller single mode detectors. A brief note is provided in the conclusion of this paper, addressing a novel, more elegant solution to modelling far-infrared interferometers, which holds promise for improving the computational efficiency of the simulations presented here

Rectangular to Large Diameter Conical Corrugated Waveguide Converter Based on Stacked Rings

This paper considers the design and manufacture, using stacked rings, of a standard corrugated antenna for the WM-380 band for use as a converter from a WM-380 rectangular aperture to a large diameter conical corrugated waveguide. In-house mode matching software is utilised for the design and three prototypes manufactured using stacked rings. The level of agreement of the stacked ring prototypes with the design predictions for the return loss and HE11 modal coupling is measured and found to demonstrate high levels of agreement