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A high-performance low-loss high-reflection-loss compact double-ridged waveguide orthomode transducer (OMT) for the 67–116 GHz band has been designed, fabricated, and tested. The focus in the design has been to achieve the best possible performance while keeping the design compact and fabrication as simple as possible. The designed OMT is based on a double-ridged waveguide Boifot junction followed by a main arm with an E-plane bend, and two side arms which are combined into a Y-junction. Wideband performance has been achieved by careful control of the waveguide width at the waveguide junction, and by the use of a variable width septum. The design is very compact and can be fabricated by conventional computer numerical control (CNC) milling techniques in two split blocks. The output waveguides are standard WR-10 rectangular waveguides. Prototype OMTs have been fabricated and tested with good agreement with simulations. The measured insertion loss is around 0.15 dB, the reflection loss is better than 23 dB, and isolation and cross-polarization are lower than – 45 dB at all frequencies. This OMT is intended to be used in cryogenic low-noise receivers for radio astronomy. To the extent of our knowledge, this is the best reported performance for an OMT over a 55% fractional bandwidth at W-band frequencies.

ABSTRACT A smooth taper double-ridge waveguide orthomode transducer (OMT) has been designed for the new 100 GHz band receiver system on the Nobeyama Radio Observatory (NRO) 45-m radio telescope. The OMT consists of a smooth taper double-ridge waveguide followed by a Bøifot type junction with a main arm and two side arms. The main arm output is a smoothed tapered transformer followed by an E-plane bend and an oval waveguide. This design facilitates the fabrication of the OMT using split blocks machined on a CNC (computer numerical control) machine. The OMT shows a return loss of better than 18 dB, a polarization isolation of better than 28 dB, and an insertion loss of less than 0.5 dB across the 74-116 GHz, and also demonstrated the excellent performance on the NRO 45-m radio telescope.

In order to better understand the variation mechanism of ozone abundance in the middle atmosphere, the simultaneous monitoring of ozone and other minor molecular species, which are related to ozone depletion, is the most fundamental and critical method. A waveguide-type multiplexer was developed for the expansion of the observation frequency range of a millimeter-wave spectroradiometer, for the simultaneous observation of multiple molecular spectral lines. The proposed multiplexer contains a cascaded four-stage sideband-separating filter circuit. The waveguide circuit was designed based on electromagnetic analysis, and the pass frequency bands of stages 1–4 were 243–251 GHz, 227–235 GHz, 197–205 GHz, and 181–189 GHz. The insertion and return losses of the multiplexer were measured using vector network analyzers, each observation band was well-defined, and the bandwidths were appropriately specified. Moreover, the receiver noise temperature and the image rejection ratio (IRR) using the superconducting mixer at 4 K were measured. As a result, the increase in receiver noise due to the multiplexer compared with that of only the mixer can be attributed to the transmission loss of the waveguide circuit in the multiplexer. The IRRs were higher than 25 dB at the center of each observation band. This indicates that a high and stable IRR performance can be achieved by the waveguide-type multiplexer for the separation of sideband signals.

Since its inception, the Intergovernmental Panel on Climate Change (IPCC) has always been at the centre of the global climate debate. Its authoritative reports provide cultural resources for public understanding on the challenge of climate change. While the IPCC maintains its perception as a policy-neutral adviser, the IPCC in practice acts as a powerful discursive agent that guides policy debates in a certain direction by enacting influential scientific concepts. These concepts include three prominent metaphors—temperature threshold, carbon budget and climate deadline—that have been widely circulated across science, policy and advocacy. Three metaphors differ on ways in which the risk of climate change is expressed in terms of space and time. But they all constitute the discourse of climate scarcity—the cognitive view of that we have (too) little space and time to stay below a physical limit for avoiding dangerous climate change. This discursive construction of physical scarcity on climate change has significant political and psychological implications. Politically, the scarcity discourse has the risk of increasing a post-political tendency towards managerial control of the global climate (‘scarcity of politics’). Psychologically, however, scarcity has a greater risk of generating a ‘scarcity mindset’ that inhibits our cognitive capacity to imagine human life beyond managing physical scarcity. Under a narrow mindset of scarcity, the future is closed down to the ‘point of no return’ that, if crossed, is destined to be the end. To go beyond the scarcity discourse, a new discourse of emancipation has to be fostered. Climate change can be reframed not as a common single destination but as a predicament for actively reimagining human life. Such a narrative can expand our imaginative capacity and animate political action while embracing social losses.

We fabricated silicon (100) membranes of 3 mm in diameter on the surface of silicon-on-insulator (SOI) substrates and investigated the characteristics of the membranes. The handle layer of one SOI substrate was etched using deep reactive ion etching process with the buried oxide (BOX) layer that remained together with the device layer. The BOX layer of the other SOI substrate was removed using C 4 F 8 -based plasma etching after the handle layer etching. The surfaces of both silicon (100) membranes were observed using the scanning white light interferometer system at room temperature. Both silicon (100) membranes have dome-like deformations. The silicon (100) membranes are effectively flattened by etching the BOX layer under the device layer. Both silicon (100) membranes were cooled from room temperature to 4 K by a Gifford–McMahon refrigerator. Wrinkles appeared on the surfaces of both silicon (100) membranes when the temperature dropped to about 200 K. However, the wrinkles disappeared below about 180 K. This phenomenon indicates the wrinkles at low temperature would depend on the properties of the silicon (100) of the device layers and independent of the properties of the BOX layers under the silicon (100) membranes.

Ultra-wideband, three-dimensional (3D) imaging spectrometry in the millimeter–submillimeter (mm–submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution1–3. However, it is challenging to scale up conventional coherent heterodyne receivers4 or free-space diffraction techniques5 to sufficient bandwidths (≥1 octave) and numbers of spatial pixels2,3 (>102). Here, we present the design and astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer6, which covers 332–377 GHz with a spectral resolution of F/ΔF ~ 380. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs)7 with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on-sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to ~1.1 THz. The miniature chip footprint of a few cm2 allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large-volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible1–3.By using a superconducting integrated circuit to filter incoming millimetre, submillimetre and far-infrared light from distant galaxies, a prototype spectrometer holds promise for wideband spectrometers that are small, sensitive and scalable to wideband spectroscopic imagers.

This paper describes the design and development of the 2 mm band orthomode transducer (OMT) for the Band 4 cartridge receivers of the Atacama Large Millimeter/Submillimeter Array (ALMA). The OMT consists of a double-ridged waveguide followed by a Bϕifot type junction with a main arm and two side arms. The main arm output is a multi-section step transformer followed by an E-plane bend and an oval waveguide to be realized the OMT with a two-split block using conventional Computer Numerical Control (CNC) milling techniques. The prototype OMT shows return loss of better than 20 dB, cross polarization coupling of better than 30 dB and insertion loss of less than 0.4 dB across 125 – 163 GHz. Furthermore, production feasibility was demonstrated through the evaluation of seven OMTs with a production design. The design of the developed OMT is so simple that it is easily scaled to submillimeter frequencies.

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter bank and microwave kinetic inductance detector (MKID) to investigate dusty starburst galaxies in the distant universe at millimeter and submillimeter wavelengths. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV 0.4–3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of 1 σ = 4 %, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array.

This paper describes the design and test observation result of a novel waveguide image rejection filter (IRF). The IRF is based on a quadrature hybrid coupler as a backward coupling structure, followed by Band Pass Filters (BPFs), and matched loads for the image-frequency termination. A prototype IRF shows return loss of better than 18 dB, and an image rejection ratio of more than 25 dB over 4 GHz band for stratospheric ozone spectra at 110 GHz when the LO frequency and IF frequency are 104 GHz and 6 GHz, respectively. We installed the prototype IRF into an ozone-measuring system and successfully observed an ozone spectrum at 110 GHz in single sideband (SSB) mode. This IRF has the advantages of low transmission loss, compact size, and easy scalability for sub-millimeter frequencies.

The idea of the carbon budget is a powerful conceptual tool to define and quantify the climate challenge. Whilst scientists present the carbon budget as the geophysical foundation for global net-zero targets, the financial metaphor of a budget implies figuratively the existence of a ‘budget manager’ who oversees the budget balance. Using this fictive character of budget manager as a heuristic device, the paper analyses the roles of carbon dioxide removal (CDR) and solar radiation management (SRM) under a carbon budget. We argue that both CDR and SRM can be understood as ‘technologies of offset’. CDR offsets positive carbon emissions by negative emissions, whereas SRM offsets the warming from positive greenhouse gas forcing by the induced cooling from negative forcing. These offset technologies serve as flexible budgeting tools in two different strategies for budget management: they offer the promise of achieving a balanced budget, but also introduce the possibility for running a budget deficit. The lure of offsetting rests on the flexibility of keeping up an ‘appearance’ of delivering a given budget whilst at the same time easing budget constraints for a certain period of time. The political side-effect of offsetting is to change the stringency of budgetary constraints from being regulated by geophysics to being adjustable by human discretion. As a result, a budget deficit can be normalised as an acceptable fiscal condition. We suggest that the behavioural tendency of policymakers to avoid blame could lead them to resort to using offset technologies to circumvent the admission of failure to secure a given temperature target.