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Billingshurst, United Kingdom

Murk A.,University of Bern | Schroder A.,University of Bern | Winser M.,Airbus | Yichen Q.,ANSYS Inc. | Wylde R.,Thomas Keating Ltd.
2016 10th European Conference on Antennas and Propagation, EuCAP 2016 | Year: 2016

In the frame of the MetOp-SG MWS microwave radiometer, we determine the expected radiometric calibration bias caused by temperature gradients in the blackbody target. The target consists of a pyramidal array of metal pyramids coated with microwave absorber. The temperature gradients within the absorber layers are simulated using the Ansys NLT software, and the microwave volume loss density using HFSS. The effective brightness temperature of the target is obtained by integrating the product of these two spatial-depend variables. © 2016 European Association of Antennas and Propagation. Source

Holler C.M.,University of Oxford | Holler C.M.,Esslingen University of Applied Sciences | Taylor A.C.,University of Oxford | Jones M.E.,University of Oxford | And 9 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2013

We describe the development of two circularly symmetric antennas with high polarization purity and low spill-over. Both were designed to be used in an all-sky polarization and intensity survey at 5 GHz (the C-Band All-Sky Survey, C-BASS). The survey requirements call for very low cross-polar signal levels and far-out sidelobes. Two different existing antennas, with 6.1-m and 7.6-m diameter primaries, were adapted by replacing the feed and secondary optics, resulting in identical beam performances of 0.73\circ FWHM, cross-polarization better than - 50 dB, and far-out sidelobes below -70 dB. The polarization purity was realized by using a symmetric low-loss dielectric foam support structure for the secondary mirror, avoiding the need for secondary support struts. Ground spill-over was largely reduced by using absorbing baffles around the primary and secondary mirrors, and by the use of a low-sidelobe profiled corrugated feedhorn. The 6.1-m antenna and receiver have been completed and tested. Results show that the co-polar beam matches the design simulations very closely in the main beam and down to levels of - 80 dB in the backlobes. With the absorbing baffles in place the far-out (>100{\circ}) sidelobe response is reduced below -90 dB. Cross-polar response could only be measured down to a noise floor of - 20 dB but is also consistent with the design simulations. Temperature loading and groundspill due to the secondary support were measured at less than 1 K. © 1963-2012 IEEE. Source

Kawahata K.,Japan National Institute for Fusion Science | Nagayama Y.,Japan National Institute for Fusion Science | Tsuchiya H.,Japan National Institute for Fusion Science | Mase A.,Kyushu University | And 4 more authors.
Plasma and Fusion Research | Year: 2011

A broadband heterodyne radiometer system has been developed and installed on KSTAR to measure second harmonic electron cyclotron emission (ECE) at the magnetic field of 3 T. The system consisting of two radiometers (110-162GHz and 164-196GHz) can cover a frequency range of 110-196GHz. The unique and key components to construct this ECE diagnostic instrument are specially-designed detector modules and a diplexer for splitting ECE radiation with high efficiency. The minimum detectable electron temperature with a time response of 1μs is about 0.23eV. The observed signal intensity is roughly consistent with the value estimated by using characteristics of various components (waveguide components, sub-harmonic mixers, amplifiers, and intermediate frequency detectors). In this article, design considerations and preliminary ECE measurements will be described. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research. Source

Murk A.,University of Bern | Wylde R.,Thomas Keating Ltd. | Bell G.,Thomas Keating Ltd. | McNamara A.,EnerSys | And 4 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

Microwave radiometers are widely used for remote sensing and radio astronomical observations. Their absolute accuracy depends on the performance of the blackbody targets which are used for the radiometric calibration. In this paper we summarize the performance aspects of such calibration targets and present different designs for upcoming ESA missions. © 2012 IEEE. Source

McKay J.E.,National HighMagnetic Field Laboratory | Robertson D.A.,University of St. Andrews | Speirs P.J.,Ecole Polytechnique Federale de Lausanne | Hunter R.I.,University of St. Andrews | And 3 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2016

We demonstrate that very high performance, extremely compact, scalar corrugated feedhorns can be designed and constructed by optimizing the excitation and phasing of the HE11, HE12, and HE13 modes near the throat of the horn while limiting excitation of higher order modes. We present the design and measurement of two families of dualprofiled horn, both with a directivity of 20 dBi that couple with very high efficiency to a fundamental Gaussian mode. The first was optimized for sidelobe performance and features sidelobes approaching .60 dB for a horn length of only 15.6. The second was designed to minimize horn length and to achieve sidelobe levels below .35 dB for a horn that is only 4.8 long. The horns exhibit excellent coupling to the fundamental freespace Gaussian mode, with LG00 power coupling of 99.92% and 99.75%, respectively. We demonstrate excellent agreement between simulation and experiment at 94 GHz and simulate the performance over a 20% bandwidth. High-performance compact scalar horns are of interest because they reduce manufacturing risk at high frequencies, and reduce size and weight at lower frequencies, which can be important in horn arrays and space applications, where horn arrays often have serious weight and size restrictions © 2016 IEEE. Source

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