The Mapper of the IGM Spin Temperature (MIST) is a new ground-based, single-antenna, radio experiment attempting to detect the global 21 cm signal from the Dark Ages and Cosmic Dawn. A significant challenge in this measurement is the frequency-dependence, or chromaticity, of the antenna beam directivity. MIST observes with the antenna above the soil and without a metal ground plane, and the beam directivity is sensitive to the electrical characteristics of the soil. In this paper, we use simulated observations with MIST to study how the detection of the global 21 cm signal from Cosmic Dawn is affected by the soil and the MIST beam directivity. We simulate observations using electromagnetic models of the directivity computed for single- and two-layer models of the soil. We test the recovery of the Cosmic Dawn signal with and without beam chromaticity correction applied to the simulated data. We find that our single-layer soil models enable a straightforward recovery of the signal even without chromaticity correction. Two-layer models increase the beam chromaticity and make the recovery more challenging. However, for the model in which the bottom soil layer has a lower electrical conductivity than the top layer, the signal can be recovered even without chromaticity correction. For the other two-layer models, chromaticity correction is necessary for the recovery of the signal and the accuracy requirements for the soil parameters vary between models. These results will be used as a guideline to select observation sites that are favorable for the detection of the Cosmic Dawn signal.

The increment in the demand for high-frequency monolithic integrated circuits has driven the development of waveguide-to-microstrip transition that allow their characterization and integration with waveguide components. Unfortunately, when return losses are taken into account, these transitions feature a rather narrow bandwidth, especially when the substrate is inserted transversal to the propagation direction of the waveguide. Here, we present a new scalable design that overcomes this problem. The transition was originally designed for a bandwidth of 33.5–60 GHz (extended V-band) with the simulation results showing reflections below − 19.5 dB in a fractional bandwidth of 55

The increment in the demand for high-frequency monolithic integrated circuits has driven the development of waveguide-to-microstrip transition that allow their characterization and integration with waveguide components. Unfortunately, some of these transitions currently feature a rather narrow bandwidth, especially when the substrate is inserted transversal to the propagation direction of the waveguide. Here we present a new design that overcomes this problem. The transisition was originally designed for a bandwidth of 33.5–60 GHz (extended V-Band) with the simulation results showing reflections below −19.5 dB in a fractional bandwidth of 55% and, moreover, can be scaled to other frequencies keeping good electrical characteristics. To validate the design we show the scaling, construction, and measurement in an extended Q-band (27–50 GHz) with the additional advantage of having a standard impedance of 50 Ω. The most novel feature is a staggered air cavity for the microstrip and planar probe, which generates return losses better than 20 dB in a fractional bandwidth of 53%.

In this communication, we present a miniaturized multiband metamaterial (MTM)-based antenna for array applications, operating with good radiation performance over the long term evolution (LTE) and Universal Mobile Telecommunications System (UMTS) uplinks within the 800–3000 MHz range. Each antenna element consists of a radiator and an MTM reflector. The former is a miniaturized Archimedean spiral antenna with an integrated matching line. The latter is placed 39 mm below the radiator and is shared among the multiple elements in the array application. The radiator is very compact, a square of 75 mm per side, equivalent to only 0.2 (0.75) times the free-space wavelength at 800 MHz (3000 MHz). The reflector is incorporated to achieve half-space radiation and is implemented with a novel multilayered MTM structure to improve the radiation efficiency. The MTM, moreover, is used in a nonconventional way. In fact, we take advantage of its complete phase-response function, behaving, thus, as a magnetic or electric conductor in different parts of the band. In this way, the in-phase reflection is not limited by the typical narrow bandwidth of artificial magnetic conductors. The measured $S_{11}$ parameter is less than −8 dB and the simulated gain is greater than 4.2 dBi in a range exceeding the one covered by the UMTS and LTE uplinks. Furthermore, a $2\times 2$ antenna array was also built. The reflections of each element are similar to those obtained in the single-element antenna.

When packaging large-width microwave integrated circuits, care has to be taken to avoid structures that could sustain unwanted oscillations. Unfortunately, this situation may not be attainable since large holding cavities are prone to support parasitic waveguide modes that could produce a feedback loop which, in turn, is especially dangerous in high-gain components with poor match with subsequent elements. This letter presents an scalable metasurface, implemented as a gap-waveguide perfect magnetic conductor, suitable to overcome this problem in millimeter- and submillimeter-band receivers. The proposed solution was integrated into a compact $W$ -band (75–110 GHz) receiver where a large chip-width amplifier was placed near a mixer, thus generating oscillations at high-gain levels compromising its operation at some frequencies. The metasurface was incorporated at the top of the amplifier's cavity where it did not only suppressed completely the oscillation, but also increased isolation between components. As a result, the receiver became fully operational as attested by measurements of its noise temperature at the compromised frequencies.

Sideband Ratio or so called Image Rejection Ration (IRR), is one of the key figures of merit of sideband separating (2SB) receivers. Although these kind of receivers are widely used in ground-based astronomy, a full description of their IRR pattern has not been performed yet. To solve this problem we have simulated the entire 2SB SIS receiver by combining models of RF and IF chains. It was found that a bottle neck of the IRR performance is not in an imbalance of individual RF and IF components, but in system imbalances determined by parasitic reflections in RF and IF chains. Using that knowledge we have built a 2SB receiver based on SIS mixers for the APEX telescope in Chile, which has a state-of-the-art performance at frequencies 600-720 GHz.

Implementation 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.

By using acoustic emission (AE) it is possible to control deviations and surface quality during micro milling operations. The method of micro milling is used to manufacture a submillimetre waveguide where micro machining is employed to achieve the required superior finish and geometrical tolerances. Submillimetre waveguide technology is used in deep space signal retrieval where highest detection efficiencies are needed and therefore every possible signal loss in the receiver has to be avoided and stringent tolerances achieved. With a sub-standard surface finish the signals travelling along the waveguides dissipate away faster than with perfect surfaces where the residual roughness becomes comparable with the electromagnetic skin depth. Therefore, the higher the radio frequency the more critical this becomes. The method of time-frequency analysis (STFT) is used to transfer raw AE into more meaningful salient signal features (SF). This information was then correlated against the measured geometrical deviations and, the onset of catastrophic tool wear. Such deviations can be offset from different AE signals (different deviations from subsequent tests) and feedback for a final spring cut ensuring the geometrical accuracies are met. Geometrical differences can impact on the required transfer of AE signals (change in cut off frequencies and diminished SNR at the interface) and therefore errors have to be minimised to within 1 µm. Rules based on both Classification and Regression Trees (CART) and Neural Networks (NN) were used to implement a simulation displaying how such a control regime could be used as a real time controller, be it corrective measures (via spring cuts) over several initial machining passes or, with a micron cut introducing a level plain measure for allowing setup corrective measures (similar to a spirit level).

This work presents a complete study of the optical system for ALMA band 1, which covers the frequency range from 35 to 50 GHz, with the goal of extending the coverage up to 52GHz. Several options have been explored to comply with the stringent technical specifications, restrictions, and cost constraints. The best solution consists of a corrugated zoned lens, two infrared filters and a spline profiled corrugated horn. The calculated aperture efficiency is better than 75%, while the average noise contribution is lower than 10.3 K. The first prototypes of the system have been constructed and first evaluation results available

A central component of a sideband separating (2SB) receiver is the quadrature hybrid which splits the incoming radio frequency signal into two branches with a 90 degrees-phase shift. Its fabrication, however, is one of the factors limiting the operational bandwidth and the maximum frequency at which a 2SB can be built. In this paper a 100%-photonic approach to produce this split is presented. In this way, wider operational bandwidth and a higher maximum operational frequency could be achieved. We also present the first experimental results of a proof-of-concept implementation at 55 MHz that studied the phase stability and controllability of this approach using a commercial 90-degree optical hybrid.

In this work we present a Q-band waveguide orthomode transducer (OMT) based on a dual ridge structure. It was designed to be used in astronomical projects were an excellent broad-band performance is mandatory. Of particular interest is the case of ALMA Band 1 (originally set at 31-45 GHz) project which will need several OMTs with outstanding performance and demonstrated manufacturability. By using a symmetrical structure, low cross-polar level and good input matching are achieved over a broad bandwidth (37 %). The proposed design incorporates an octagonal mode converter which allows the unit to be directly mated with the horn avoiding cross-polar issues at the interface. The OMT was designed to have a compact configuration and easiness of fabrication, both crucial features in projects where several units (up to 70) have to be constructed.

More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a traveling-wave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University.

In this paper we describe the status of an upgrading program that it is being carried out to modernize the front and back ends of the Southern 1.2-m mm-Wave Telescope to cover eciently the band from 86 to 115 GHz. On the one hand, the new front end will have a sideband-separating conguration to suppress the image band noise. This front end will use one low noise amplier and two Schottky diodes for down conversion. On the other hand, we are developing a modern digital spectrometer, based on the Recongurable Open Architecture Computing Hardware (ROACH), to ease the operation and improve the spectral resolution up to a factor of 4. Moreover, the spectrometer will include IF hybridization capabilities to avoid analog hybrids and, therefore, improve the sideband rejection ratio of the receiver.

We study, using niobium- technology, the bandwidth of SIS mixers operating at frequencies close to the energy-gap frequency. Microstriplines of niobium- silicon dioxide-niobium have different properties for the top and bottom superconductor, which we find to depend on the used fabrication process. Replacing the AlOx tunnel barrier by AlN, the bandwidth increases by 53%. The measurements, using a Fourier Transform Spectrometer (FTS) and performed in ambient air, demonstrate that the bandwidth is no longer limited by the tuning circuit but by the atmospheric absorption of radiation. Excellent noise temperatures are found over a full band of 600 to 720 GHz.