Complex dielectric permittivity of engineering and 3D-printing polymers at Q-band

\u3cp\u3eWe report experimental values of the complex dielectric permittivity of a wide variety of engineering polymers. Measurements were done using the filling waveguide method at Q-band (30–50 GHz), being representative of the values over the millimeter wave regime. This method has a high accuracy, providing excellent wide-bandwidth characterization. Measured samples include the most common engineering materials as polyamide, polyethylene, polytetrafluoroethylene, polyoxymethylene, polylactic acid, phenol formaldehyde resin, polypropylene, polyvinyl chloride, acrylonitrile butadiene styrene, polyphenyle sulfide, and polyether ether ketone. Results are comprehensive and represent an important contribution to the technical literature which lacks of material measurements at these frequencies. Of particular interest are samples of 3D printed materials and high performance polymers, that will probably find new and novel applications in the field of microwave components and antennas for the millimeter wave band.\u3c/p\u3

Systematic study of the cross polarization introduced by broadband antireflection layers at microwave frequencies

\u3cp\u3eImplementation of antireflection layers using structured materials is of common use in millimeter-and submillimeter-wave refractive optic systems. In this work we have systematically studied the effect of such structures in the optical propagation with special emphasis on the cross polarization they introduce. We have performed extensive simulations and experimental verification of several commonly used structures: concentric grooves, parallel grooves, an array of boxes, an array of cylinders, and rectangular-versus triangular-shaped grooves. As a result, we propose optimal structures for demanding applications in terms of polarization and return losses over large fractional bandwidths.\u3c/p\u3

ALMA Band 1 Optics (35–50 GHz):Tolerance analysis, effect of cryostat infrared filters and cold beam measurements

\u3cp\u3eThe Atacama Large Millimeter/Sub-millimeter Array (ALMA) is currently the largest (sub-)mm wave telescope in the world and will be used for astronomical observations in all atmospheric windows from 35 to 950 GHz when completed. The ALMA band 1 (35–50 GHz) receiver will be used for the longest wavelength observations with ALMA. Because of the longer wavelength, the size of optics and waveguide components will be larger than for other ALMA bands. In addition, all components will be placed inside the ALMA cryostat in each antenna, which will impose severe mechanical constraints on the size and position of receiver optics components. Due to these constraints, the designs of the corrugated feed horn and lens optics are highly optimized to comply with the stringent ALMA optical requirements. In this paper, we perform several tolerance analyses to check the impact of fabrication errors in such an optimized design. Secondly, we analyze the effects of operating this optics inside the ALMA cryostat, in particular the effects of having the cryostat IR filters placed next to the band 1 feed horn aperture, with the consequent near-field effects. Finally, we report on beam measurements performed on the first three ALMA band 1 receivers inside test cryostats, which satisfy ALMA specifications. In these measurements, we can clearly observe the effects of fabrication tolerances and IR filter effects on prototype receiver performance.\u3c/p\u3

High efficiency wideband refractive optics for ALMA band-1 (35-52 GHz):Design, Implementation, and Measurement Results

We present the design, implementation, and characterization of the optics of ALMA Band 1, the lowest frequency band in the most advanced radio astronomical telescope. Band 1 covers the broad frequency range from 35 to 50 GHz, with the goal of minor degradation up to 52 GHz. This is, up to now, the largest fractional bandwidth of all ALMA bands. Since the optics is the first subsystem of any receiver, low noise figure and maximum aperture efficiency are fundamental for best sensitivity. However, a conjunction of several factors (small cryostat apertures, mechanical constraints, and cost limitations) makes extremely challenging to achieve these goals. To overcome these problems, the optics presented here includes two innovative solutions, a compact optimized-profile corrugated horn and a modified Fresnel lens. The horn profile was optimized for optimum performance and easy fabrication by a single-piece manufacturing process in a lathe. In this way, manufacturability is eased when compared with traditional fabrication methods. To minimize the noise contribution of the optics, a one-step zoned lens was designed. Its parameters were carefully optimized to maximize the frequency coverage and reduce losses. The optical assembly reported here fully complies with ALMA specifications

67–116 GHz optics development for ALMA band 2–3 receivers

In this paper we report the first results of the optical components development and the overall optical design for a wideband receiver to simultaneously cover ALMA bands 2 and 3. Two types of feed horns and OMTs have been designed to couple to the ALMA telescope beam using a modified Fresnel lens. Both types of hardware have been manufactured and tested in a near field beam scanner. The measured beam patterns and optical efficiencies are in good agreement with simulations

Optimized corrugated tapered slot antenna for mm-wave applications

\u3cp\u3eWe present a novel approach to design a highperformance tapered slot antenna (TSA) at millimeter-wave frequencies. Commonly, TSAs are designed using profiles expressed as simple functions (linear, exponential, Fermi, or constant width). Some improvement can be achieved by the use of corrugations of fixed dimensions. This usual approach, however, gives little room for improvement in their performance. To overcome this situation, we have developed a new approach: The use of a nonspecific profile and variable corrugations along the antenna, both of which can be optimized to considerably improve its performance. For the optimization, we have used a particle-swarm algorithm allowing us to achieve an excellent performance in the entire W-band. To demonstrate the efficiency of this new approach, we have implemented an optimized antenna using standard printed circuit board (PCB)-prototyping methods. Across the whole W-band, the constructed antenna shows sidelobe levels, reflection coefficient, and cross polarization below-16,-10, and-25 dB, respectively. These results are in good agreement with simulations which also predict possible operation down to 60 GHz. Finally, given its small footprint and the fact that it has been fed by a microstrip line, this antenna can be used in compact electronics providing excellent performance such as that required in radio astronomy or telecommunications.\u3c/p\u3

ALMA band 2+3 (67–116 GHz) optics:design and first measurements

The ALMA telescope is one of the largest on-ground astronomical projects in the world. It has been producing great scientific results since the beginning of operations in 2011. Of all the originally planned bands, band 2 (67-90 GHz) is the last band to be implemented into the array. Recent technological progress has open the possibility to combine bands 2 and 3 (84-116 GHz) into a single wideband receiver. This paper describes the first efforts to design wideband optics which cover both bands, from 67 to 116 GHz, using a profiled corrugated horn and a modified Fresnel lens. First measurements were performed at ESO in Dec15-Jan16 and showed good agreement with simulations

Performance of the first three preproduction 35-50 GHz receiver front-ends for atacama large millimeter / submillimeter array

\u3cp\u3eThe Band-1 receiver front-end cartridges for Atacama Large Millimeter Array, which covered 35-50 GHz frequency range, are now in preproduction stage. For the first three preproduction cartridges, the measured receiver noise temperature is less than 16-31K for any combination of the inband RF and LO frequencies. The measured gain flatness, even with the limitation of the optical window of the cryostat and the broadband matching of the cryogenic amplifiers, is typically lower than 5 dB over any 2GHz window. Extracted aperture beam efficiency is typically higher than 80% over the full frequency range. The crosstalk over the orthogonal channel is lower than-63 dB. For the suppression of the unwanted lower sideband, the imaged band suppression is higher than 20 dB for the worst case and around 30 dB typically.\u3c/p\u3

Performance of the first three preproduction 35–50 GHz receiver front-ends for atacama large millimeter / submillimeter array

The Band-1 receiver front-end cartridges for Atacama Large Millimeter Array, which covered 35-50 GHz frequency range, are now in preproduction stage. For the first three preproduction cartridges, the measured receiver noise temperature is less than 16-31K for any combination of the inband RF and LO frequencies. The measured gain flatness, even with the limitation of the optical window of the cryostat and the broadband matching of the cryogenic amplifiers, is typically lower than 5 dB over any 2GHz window. Extracted aperture beam efficiency is typically higher than 80% over the full frequency range. The crosstalk over the orthogonal channel is lower than -63 dB. For the suppression of the unwanted lower sideband, the imaged band suppression is higher than 20 dB for the worst case and around 30 dB typically

Wideband 67−116 GHz receiver development for ALMA Band 2

Context. The Atacama Large Millimeter/submillimeter Array (ALMA) has been in operation since 2011, but it has not yet been populated with the full suite of its planned frequency bands. In particular, ALMA Band 2 (67−90 GHz) is the final band in the original ALMA band definition to be approved for production.\u3cbr/\u3e\u3cbr/\u3eAims. We aim to produce a wideband, tuneable, sideband-separating receiver with 28 GHz of instantaneous bandwidth per polarisation operating in the sky frequency range of 67−116 GHz. Our design anticipates new ALMA requirements following the recommendations of the 2030 ALMA Development Roadmap.\u3cbr/\u3e\u3cbr/\u3eMethods. The cryogenic cartridge is designed to be compatible with the ALMA Band 2 cartridge slot, where the coldest components – the feedhorns, orthomode transducers, and cryogenic low noise amplifiers – operate at a temperature of 15 K. We use multiple simulation methods and tools to optimise our designs for both the passive optics and the active components. The cryogenic cartridge is interfaced with a room-temperature (warm) cartridge hosting the local oscillator and the downconverter module. This warm cartridge is largely based on GaAs semiconductor technology and is optimised to match the cryogenic receiver bandwidth with the required instantaneous local oscillator frequency tuning range.\u3cbr/\u3e\u3cbr/\u3eResults. Our collaboration has resulted in the design, fabrication, and testing of multiple technical solutions for each of the receiver components, producing a state-of-the-art receiver covering the full ALMA Band 2 and 3 atmospheric window. The receiver is suitable for deployment on ALMA in the coming years and it is capable of dual-polarisation, sideband-separating observations in intermediate frequency bands spanning 4−18 GHz for a total of 28 GHz on-sky bandwidth per polarisation channel.\u3cbr/\u3e\u3cbr/\u3eConclusions. We conclude that the 67−116 GHz wideband implementation for ALMA Band 2 is now feasible and that this receiver provides a compelling instrumental upgrade for ALMA that will enhance observational capabilities and scientific reach.\u3cbr/\u3e\u3cbr/\u3eKey words: instrumentation: interferometer