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

Tapia, Valeria; Rodríguez, Rafael; Reyes, Nicolás; Mena, F. P.; Yagoubov, P.; Cuttaia, F.; Bronfman, L.

doi:10.1364/ao.57.009223

Cited by 6 publications

(3 citation statements)

References 16 publications

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“…We studied the adequacy of different geometrical profiles, based on the systematic review of different structures with a special emphasis on cross-polarization presented in [19]. [19] concluded that better performance is achieved when using perpendicular geometries versus concentric structures, although the manufacturing process is more complicated. The choice of the geometry was driven first by the achieved performance and whether we met requirements, and second, by the simplicity of construction.…”

Section: Design and Verification Methodologymentioning

confidence: 99%

The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10–20 GHz sky spectra

et al. 2021

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The TMS optical system is based on a decentered dual-reflector system in a Gregorian configuration to observe with an angular resolution of less than 2°. The primary goal of the present study is to evaluate the final design and verify that it satisfies the design requirements. We aim for low cross-polarization (-30 dB), low sidelobe (-25 dB) levels, and a stable beam in terms of shape (low ellipticity) and size over a full octave bandwidth (10–20 GHz). We performed both ray-tracing and full-wave simulations using the CST Studio software in order to investigate the system behaviour. We gave special attention to the beam frequency variation and polarization leakage. We have characterized the effects on the radiation pattern produced by the cryostat window. We present the final design of the TMS optical system, as well as a complete study of the system's performance in terms of cross-polarization, sidelobes, ellipticity and beamwidth. We discuss the effects of sidelobes and study the need for a baffle.

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Section: Design and Verification Methodologymentioning

confidence: 99%

The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10–20 GHz sky spectra

et al. 2021

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“…In order to minimise the loss due to reflection at the air-lens and lens-vacuum transitions, we employed AR surfacing techniques that result in meta-material surfaces. The full results from five different approaches for the AR are presented in Tapia et al (2018), which compares the noise contribution, cross-polarisation leakage, reflection loss, and beam and polarisation efficiencies.…”

Section: Lens Designsmentioning

confidence: 99%

“…HDPE has served as a standard window and lens material for ALMA and many other mm/submm-wave observatories, but has the drawback of a relatively high dielectric loss (see e.g. Lamb 1996;Tapia et al 2018). In order to minimise the total insertion loss in the HDPE lens, we have designed and implemented a Fresnel zoned lens.…”

Section: Lens Designsmentioning

confidence: 99%

Wideband 67−116 GHz receiver development for ALMA Band 2

Yagoubov

Mroczkowski

Belitsky

et al. 2020

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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. Aims. 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. Methods. 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. Results. 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. Conclusions. 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. 1 https://www.almaobservatory.org of construction. Recent technological developments in cryogenic monolithic microwave integrated circuits (MMICs) and optical components, such as wide bandwidth feedhorns, orthomode transducers (OMT), and lens designs -have opened up the opportunity to extend the originally-planned radio-frequency (RF) bandwidth of this receiver, to cover the 67-116 GHz frequency range on-sky with a single receiver. This holds the potential for combining ALMA Band 2 (67-90 GHz) with ALMA Band 3 (84-116 GHz), serving as an upgrade that paves the way for wider bandwidth ALMA operations. As discussed in Mroczkowski et al. 2019a, this approach offers several opera-Article number, page 1 of 23

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Development of seven-beam optics using dielectric lenses for a new 72–116 GHz receiver in the Nobeyama 45 m telescope

Yamasaki¹,

Yoneyama²,

Kawashita³

et al. 2023

Publications of the Astronomical Society of Japan

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We developed a new seven-beam heterodyne receiver “7BEE” in the 72–116 GHz band for the Nobeyama 45 m telescope to investigate the early stage of star formation by deriving the deuterium fraction of dense cores. The optics for the receiver employs wideband corrugated horns covering the 72–116 GHz band and dielectric lenses to couple the incoming radiation from the antenna on to the feeds. One of the important aspects in the lens design is the anti-reflection (AR) structure to mitigate the reflections on the lens surfaces. Triangular grooves, which gradually change the effective refractive index from air to dielectric, were adopted as a basic AR design since the return loss can be in the order of 20 dB or better. The main goal of this study is to compare the radio frequency (RF) characteristics of the lenses with different patterns and sizes of AR grooving structures. We confirmed that concentric grooves degraded beam symmetry, cross-polarization characteristics, and aperture efficiency due to the birefringence of the grooves, which gave rise to wavefront distortions. Straight grooves of two different gap widths, 1.2 mm and 1.7 mm, were compared and showed similar good performance in terms of beam patterns and noise contribution. However, the latter showed a few percent higher aperture efficiency. Therefore, the straight grooves with 1.7 mm gap width were adopted as the AR structure of our lens.

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

Cited by 6 publications

References 16 publications

The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10–20 GHz sky spectra

The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10–20 GHz sky spectra

Wideband 67−116 GHz receiver development for ALMA Band 2

Development of seven-beam optics using dielectric lenses for a new 72–116 GHz receiver in the Nobeyama 45 m telescope

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