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The PLANCK mission of the European Space Agency is devoted to produce sky maps of the cosmic microwave back- ground radiation. The low-frequency instrument is a wide-hand cryogenic microwave radiometer array operating at 30, 44, and 70 GHz. The design, test techniques, and performance of the complete differential radiometer at 30 GHz are presented. This elegant breadboard 30-GHz radiometer is composed of a front-end module (FEM) assembled at the Jodrell Bank Observatory, Cheshire, U.K., and a back-end module assembled at the Universidad de Cantabria, Cantabria, Spain, and Telecomunicació, Universitat Politécnica de Catalunya, Barcelona, Spain. The system noise temperature was excellent, mainly due to the very low noise performance of the FEM amplifiers, which achieved an average noise temperature of 9.4 K. [ABSTRACT FROM AUTHOR]

A novel full-band (40% relative bandwidth) waveguide polar modulator (WPM) design based on a new architecture with two turnstile junctions and a nearly frequency-independent differential 180° phase shift between orthogonal arms is presented. The use of suitably designed turnstile junctions together with antiphase waveguide-coaxial-waveguide transitions in reduced-height waveguide technology enables the improvement of bandwidth over previous WPMs with a very compact and simple solution. This design enables continuous rotation about its central axis at 40 revolutions/s, which makes the modulator suitable for receivers with significant $1/f$ noise such as cryogenic radiometers. The polar modulator presented in this paper is designed to be cooled down to cryogenic temperatures in order to reduce its contribution to the receiver noise. This design is suitable for radio astronomy applications due to its cost-effective, compact design, and high quality performance as well as being readily scalable. A polar modulator in the Ka-band (26.5–40 GHz) has been designed to show a reflection better than −20 dB, an insertion loss around 0.3 dB, and a cross-coupling near −35 dB measured at room temperature ( $T = 298$ K). This insertion loss is reduced by 30%, while the phase difference and cross-coupling maintain similar values when the polar modulator is cooled to approximately $T = 80$ K. [ABSTRACT FROM AUTHOR]

This paper presents preliminary polarization measurements and systematic-error characterization of the Thirty Gigahertz Instrument receiver developed for the QUIJOTE experiment. The instrument has been designed to measure the polarization of Cosmic Microwave Background radiation from the sky, obtaining the Q, U, and I Stokes parameters of the incoming signal simultaneously. Two kinds of linearly polarized input signals have been used as excitations in the polarimeter measurement tests in the laboratory; these show consistent results in terms of the Stokes parameters obtained. A measurement-based systematic-error characterization technique has been used in order to determine the possible sources of instrumental errors and to assist in the polarimeter calibration process. [ABSTRACT FROM AUTHOR]

This paper presents the analysis, design, and characterization of the thirty gigahertz instrument receiver developed for the Q-U-I Joint Tenerife experiment. The receiver is aimed to obtain polarization data of the cosmic microwave background radiation from the sky, obtaining the Q, U, and I Stokes parameters of the incoming signal simultaneously. A comprehensive analysis of the theory behind the proposed receiver is presented for a linearly polarized input signal, and the functionality tests have demonstrated adequate results in terms of Stokes parameters, which validate the concept of the receiver based on electronic phase switching. [ABSTRACT FROM AUTHOR]

A >40% bandwidth fully scalable turnstile-based waveguide orthomode transducer having excellent phase performance is described for the WR75 standard rectangular waveguide. Flexible bandwidth tuning is achieved through the use of an interchangeable stepped scattering element. Reduced height waveguide topology provides a simple, compact, and robust design against mechanical tolerances. The intrinsic broadband nature of half-height E-plane bends and single-step power combiners assures high order mode free increased bandwidth in balanced phase operation. The designed orthomode transducer exhibits a return loss better than 23 dB at any port, an insertion loss less than 0.06 dB, and an isolation of 50 dB over the full bandwidth. Moreover, the phase difference between orthogonal polarizations is lower than 0.7° over the band, thus enabling applications where phase-matched outputs are required. This design has been chosen for the QUIJOTE cosmic microwave background experiment due to its cost-effective, compact design, and high-quality performance as well as being readily scalable to the WR51 and WR28 waveguide bands. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [ABSTRACT FROM AUTHOR]

This paper presents a built-in calibration procedure of a 10-to-20 GHz polarimeter aimed at measuring the I, Q, U Stokes parameters of cosmic microwave background (CMB) radiation. A full-band square waveguide double directional coupler, mounted in the antenna-feed system, is used to inject differently polarized reference waves. A brief description of the polarimetric microwave radiometer and the system calibration injector is also reported. A fully polarimetric calibration is also possible using the designed double directional coupler, although the presented calibration method in this paper is proposed to obtain three of the four Stokes parameters with the introduced microwave receiver, since V parameter is expected to be zero for the CMB radiation. Experimental results are presented for linearly polarized input waves in order to validate the built-in calibration system. [ABSTRACT FROM AUTHOR]