Juan L. Cano

The Quijote CMB Experiment

We present the current status of the QUIJOTE (Q-U-I JOint TEnerife) CMB Experiment, a new instrument which will start operations early in 2009 at Teide Observatory with the aim of characterizing the polarization of the CMB and other processes of galactic and extragalactic emission in the frequency range 10–30GHz and at large angular scales. QUIJOTE will be a valuable complement at low frequencies for the PLANCK mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r = 0.05.

Octave Bandwidth Compact Turnstile-Based Orthomode Transducer

A 64% instantaneous bandwidth scalable turnstile-based orthomode transducer to be used in the so-called extended C-band satellite link is presented. The proposed structure overcomes the current practical bandwidth limitations by adding a single-step widening at the junction of the four output rectangular waveguides. This judicious modification, together with the use of reduced-height waveguides and E-plane bends and power combiners, enables to approach the theoretical structure bandwidth limit with a simple, scalable and compact design. The presented orthomode transducer architecture exhibits a return loss better than 25 dB, an isolation between rectangular ports better than 50 dB and a transmission loss less than 0.04 dB in the 3.6-7 GHz range, which represents state-of-the-art achievement in terms of bandwidth.

Ultra-Wideband Chip Attenuator for Precise Noise Measurements at Cryogenic Temperatures

A 20-dB chip attenuator designed for cryogenic noise measurements from dc up to 40 GHz is presented. The chip is based on the use of temperature-stable tantalum-nitride thin-film resistors, a high thermal conductivity substrate such as crystal quartz (z-cut), and a suitable design that avoids inner conductor thermal heating, which is an important limiting factor for the precision of cryogenic noise measurements. A high-accuracy temperature sensor installed inside the attenuator module provides precise temperature characterization close to the chip location. The high thermal conductivity of the chip substrate in the designed attenuator assures a negligible temperature gradient between the resistive elements in the chip and the sensor, thus improving the measurement accuracy. The attenuator also shows an excellent electrical performance with insertion losses of 19.9 dB ± 0.65 dB and return losses better than 20.6 dB in the whole frequency range at 296 K. The insertion loss change when cooled to 15 K is less than 0.25 dB, which demonstrates its temperature stability.

The QUIJOTE-CMB experiment: studying the polarisation of the galactic and cosmological microwave emissions

The QUIJOTE (Q-U-I JOint Tenerife) CMB Experiment will operate at the Teide Observatory with the aim of characterizing the polarisation of the CMB and other processes of Galactic and extragalactic emission in the frequency range of 10-40GHz and at large and medium angular scales. The first of the two QUIJOTE telescopes and the first multi-frequency (10-30GHz) instrument are already built and have been tested in the laboratory. QUIJOTE-CMB will be a valuable complement at low frequencies for the Planck mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r = 0.05.

Full-Band Air-Filled Waveguide-to-Substrate Integrated Waveguide (SIW) Direct Transition

A 45% bandwidth in-line air-filled waveguide-to-substrate integrated waveguide (SIW) direct transition is designed to greatly improve the performance of existing configurations. The transition, based on a four-section height-stepped waveguide, includes a single-step widening transformer that enables full-band operation without using any dielectric probe. The absence of the probe reduces significantly the insertion loss and makes this transition simple, bandwidth controllable and easily scalable to the millimeter-wave frequency range. A back-to-back transition is designed to cover the 32-50 GHz band showing a return loss of 15 dB and a mean insertion loss of 0.68 dB in the whole bandwidth.

On the Octave Bandwidth Properties of Octagonal-Shaped Waveguide Mode Transformers

An octave bandwidth concept for compact rectangular-to-circular and square-to-circular waveguide transitions based on the use of intermediate octagonal-shaped sections is presented. Apart from its inherent bandwidth capability and spurious mode free operation, this architecture offers some other useful advantages such as easy fabrication, low losses, and extremely short length (less than 0.75 λ0 , with λ0 being the wavelength at the center frequency), which allows their use in the millimeter-wave frequency range. Experimental verification is provided through the measurement of a rectangular-to-circular mode transformer covering more than the super-extended C -band (3.6-7.025 GHz) with 30-dB return loss and 0.1-dB insertion loss, which represents state-of-the-art performance in terms of bandwidth.

The thirty gigahertz instrument receiver for the Q-U-I Joint Tenerife experiment: concept and experimental results

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.

Cryogenic Ka-Band 180

A Ka-band hybrid 0/180° phase switch working at cryogenic temperature is presented. The circuit is designed on an alumina substrate using uniplanar hybrid technology, combining air-bridged coplanar waveguides and slotlines. Schottky diodes are used as switching elements, taking advantage of their cryogenic behavior, with low equivalent series resistance and low capacitance. Cryogenic performance at 15 K shows a phase difference response of 177 ±2°, average insertion losses of 1 dB and amplitude imbalance of less than 0.2 dB between states in the frequency range from 24 to 37 GHz (40% relative bandwidth) with a low-power consumption of 10.5 mW. The low insertion loss and small phase error make the designed phase switch suitable to be used on radioastronomy receivers (QUIJOTE experiment 26-36 GHz band) minimizing the total system noise temperature.

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This paper presents the design, simulation and measurement of a broadband back-end module (BEM) for radio-astronomy applications in the Ka-band. It is a direct conversion receiver based on low noise amplification, band pass filtering and Schottky diode detection. System simulations are based on individual linear-subsystems S-parameters measurements together with non-linear detector model. Measurements show more than 30 dB of RF gain over the 26 to 36 GHz band with a noise figure below 3.9 dB. Detected voltage is in the range 1-10 mV which meets the application specifications.

Phase Switch Based on Schottky Diodes

A highly compact and efficient dual-mode power divider suitable for multi-level (4N) beam-forming networks is presented. Circular waveguide dual polarization is accomplished by using a symmetric 4:1 turnstile-like topology and strategic cavity resonance suppressors to achieve more than 20% bandwidth operation with a theoretical 35 dB cross-polar discrimination. Experimental verification for a Ku-band (10.5-13 GHz) dual-mode four-way power divider is presented, showing a common port return loss better than 20 dB, an input-output isolation (orthogonal modes) better than 30 dB, and an insertion loss around 0.25 dB.