Final Report Summary - ITERATE (Improved heTErodyne Receiving Arrays for TEraherzt applications)
Sensors at sub-millimeter wavelengths, which is loosely defined as 100 GHz to 3 THz, provide unprecedented sensitivity for astrophysics, planetary science, Earth observation, medical imaging or security screening. Heterodyne receivers, which down-convert radio frequency signals to intermediate frequency signals preserving the amplitude and phase information of the incoming radiation, are generally the detector of choice for high resolution sub-millimeter wave spectroscopy. Heterodyne receivers provide both the sensitivity and resolution for such studies. This proposal deals with the development of improved heterodyne receivers for instruments in the sub-millimeter wave range for stratospheric observatories and CubeSat/SmallSats, which require higher levels of component integration with novel antenna architectures.
Some of the most elusive and important questions (from distant galaxies to our own planet’s climate) need to be solved with space-based instruments. But, the high cost of designing and launching traditional spacecraft is a hurdle that limits both what can be accomplished, and who can do it. Stratospheric observatories (like balloons or aircrafts) present some advantages with respect to ground-based observations. However, small projects cannot afford their cost. Small, modular, and inexpensive to build and launch, CubeSats are opening up space exploration like never before. They offer a new world of possibilities in research and technology development to everyone: students, universities of all sizes, technology pioneers, and crowd-sourced initiatives. They typically fly as secondary payload and can be used to enhance the science objectives of the primary mission, to enable new science in new (potentially dangerous) environments and to demonstrate novel technologies. A major challenge lies in adapting instruments to the CubeSat form factor and CubeSat-level budgets, while maintaining performances comparable to primary payloads.
Critical requirements for any Cubesat applications will be low-mass, low-power, and reduced complexity. For the majority of instruments that require high-spatial resolution, the mass of the instrument is dominated by the metallic antenna structure. For instance, one of the bulkiest part of the Microwave Instrument on the Rosetta Orbiter (MIRO) on the Rosetta mission had a 30-cm parabolic dish. Recently, the Radiometer Atmospheric CubeSat Experiment (RACE) has been conceived to detect water vapor at 183-GHz, using a 6-cm diameter offset reflector allocated inside the bus of a 3U Cubesat. An alternative consists on deploying Cassegrain antennas, with the primary reflector made of unfurlable mesh, and reflectarrays, as done up to Ka band for deep-space communications (e.g. Mars Cube One, MarCO). The latter approach adds complexity to the CubeSat on account of the deployment system, and it is difficult to apply at higher frequencies due to surface accuracy requirements. On the other hand, by placing the reflector inside the bus we lose space for other instruments. Although we have developed in the context of this project classical instruments based on feed horns and dish antennas, we are in search of alternate technology which will accomplish the same objectives but with substantially reduced mass, complexity, and risk.
One of our objectives has been the development of a low-mass, low-profile high-gain terahertz (THz) antenna, readily integrable in the CubeSat chassis, thus avoiding the mechanical complexity of deployable antennas, while saving bus space. To that end, we have investigated the use of modulated metasurfaces (MTSs). Among their advantages it is worth noting their capability of beam shaping, pointing and scanning, a simple on-surface control of the aperture fields, and all this while keeping a low profile and low envelope. In MTS antennas, an inductive surface reactance supports the propagation of a (dominantly) transverse magnetic (TM) surface-wave (SW), which is gradually radiated. Radiation is achieved by periodically modulating the equivalent reactance on the antenna aperture. The surface reactance modulation is typically achieved at microwave frequencies by changing the size and orientation of sub-wavelength patches printed on a grounded dielectric substrate, and arranged in a periodic lattice. To avoid losses in the dielectric, at higher frequencies we use instead metallic cylinders of different heights (like in a Fakir’s bed). Our structure is coupled to a rectangular waveguide (RW) input, compatible with solid-state mixers and frequency-multiplied continuous-wave sources. Both the feeder and the MTS have been micromachined out of a silicon wafer by means of deep reactive ion etching (DRIE). Integrating MTS antennas with silicon micromachined front ends, we foresee the integration of the developed THz instruments into CubeSats with 3 to 6-U volume. To the best of our knowledge, this is the first demonstration of a modulated MTS antenna at a frequency as high as 300 GHz.
A second objective has been the study of future heterodyne arrays for Stratospheric observatories. Such arrays will provide higher sensitivity, greater mapping speed, large scale mapping ability, multiple line spectroscopy, and imaging capability. Heterodyne arrays are enabled by higher levels of component integration with novel array concepts. The frequency band of interest (1.9 to 2.1 THz) has been chosen to measure spectra of gas clouds within star-forming regions in the Milky Way and nearby galaxies to investigate how interstellar clouds form, and how stars subsequently form from those clouds. High sensitivity receivers in this band require the use of HEBs, which operate at 4K, as mixer element. The conceived focal plane consists of 64 multi-flared angle smooth-walled horns, and a beam telescope in the signal path to achieve the desired f-number at the telescope’s focal plane. We have also conceived an optical distribution of the Local Oscillator to the array of detectors.
The main application of the designed receivers is in the field of sub-millimeter wave spectrometers and radiometers for planetary science. To name a few, other applications of the developed technology are: THz scanners for security screening, medical imaging, quality control in agrifood industry (detection of undesired objects or defects), and THz wireless communications, which possess the potential of providing the BW required by future wireless systems. Recent studies estimate that successful deployment of 5G could bring about 146 billion € in annual benefits for automotive, healthcare, transport and utilities industries. In addition, 5G deployment is likely to create 2.39 million jobs in the EU. This project will improve Europe’s capability of offering new solutions for major society challenges. We intend to enable the wide-spread use of THz technology in everyday life, and more traditional applications like radioastronomy and THz security screening. We believe that the proposed technology will be a milestone for the impact which volume-deployable THz technology can have on the society of the future.
Some of the most elusive and important questions (from distant galaxies to our own planet’s climate) need to be solved with space-based instruments. But, the high cost of designing and launching traditional spacecraft is a hurdle that limits both what can be accomplished, and who can do it. Stratospheric observatories (like balloons or aircrafts) present some advantages with respect to ground-based observations. However, small projects cannot afford their cost. Small, modular, and inexpensive to build and launch, CubeSats are opening up space exploration like never before. They offer a new world of possibilities in research and technology development to everyone: students, universities of all sizes, technology pioneers, and crowd-sourced initiatives. They typically fly as secondary payload and can be used to enhance the science objectives of the primary mission, to enable new science in new (potentially dangerous) environments and to demonstrate novel technologies. A major challenge lies in adapting instruments to the CubeSat form factor and CubeSat-level budgets, while maintaining performances comparable to primary payloads.
Critical requirements for any Cubesat applications will be low-mass, low-power, and reduced complexity. For the majority of instruments that require high-spatial resolution, the mass of the instrument is dominated by the metallic antenna structure. For instance, one of the bulkiest part of the Microwave Instrument on the Rosetta Orbiter (MIRO) on the Rosetta mission had a 30-cm parabolic dish. Recently, the Radiometer Atmospheric CubeSat Experiment (RACE) has been conceived to detect water vapor at 183-GHz, using a 6-cm diameter offset reflector allocated inside the bus of a 3U Cubesat. An alternative consists on deploying Cassegrain antennas, with the primary reflector made of unfurlable mesh, and reflectarrays, as done up to Ka band for deep-space communications (e.g. Mars Cube One, MarCO). The latter approach adds complexity to the CubeSat on account of the deployment system, and it is difficult to apply at higher frequencies due to surface accuracy requirements. On the other hand, by placing the reflector inside the bus we lose space for other instruments. Although we have developed in the context of this project classical instruments based on feed horns and dish antennas, we are in search of alternate technology which will accomplish the same objectives but with substantially reduced mass, complexity, and risk.
One of our objectives has been the development of a low-mass, low-profile high-gain terahertz (THz) antenna, readily integrable in the CubeSat chassis, thus avoiding the mechanical complexity of deployable antennas, while saving bus space. To that end, we have investigated the use of modulated metasurfaces (MTSs). Among their advantages it is worth noting their capability of beam shaping, pointing and scanning, a simple on-surface control of the aperture fields, and all this while keeping a low profile and low envelope. In MTS antennas, an inductive surface reactance supports the propagation of a (dominantly) transverse magnetic (TM) surface-wave (SW), which is gradually radiated. Radiation is achieved by periodically modulating the equivalent reactance on the antenna aperture. The surface reactance modulation is typically achieved at microwave frequencies by changing the size and orientation of sub-wavelength patches printed on a grounded dielectric substrate, and arranged in a periodic lattice. To avoid losses in the dielectric, at higher frequencies we use instead metallic cylinders of different heights (like in a Fakir’s bed). Our structure is coupled to a rectangular waveguide (RW) input, compatible with solid-state mixers and frequency-multiplied continuous-wave sources. Both the feeder and the MTS have been micromachined out of a silicon wafer by means of deep reactive ion etching (DRIE). Integrating MTS antennas with silicon micromachined front ends, we foresee the integration of the developed THz instruments into CubeSats with 3 to 6-U volume. To the best of our knowledge, this is the first demonstration of a modulated MTS antenna at a frequency as high as 300 GHz.
A second objective has been the study of future heterodyne arrays for Stratospheric observatories. Such arrays will provide higher sensitivity, greater mapping speed, large scale mapping ability, multiple line spectroscopy, and imaging capability. Heterodyne arrays are enabled by higher levels of component integration with novel array concepts. The frequency band of interest (1.9 to 2.1 THz) has been chosen to measure spectra of gas clouds within star-forming regions in the Milky Way and nearby galaxies to investigate how interstellar clouds form, and how stars subsequently form from those clouds. High sensitivity receivers in this band require the use of HEBs, which operate at 4K, as mixer element. The conceived focal plane consists of 64 multi-flared angle smooth-walled horns, and a beam telescope in the signal path to achieve the desired f-number at the telescope’s focal plane. We have also conceived an optical distribution of the Local Oscillator to the array of detectors.
The main application of the designed receivers is in the field of sub-millimeter wave spectrometers and radiometers for planetary science. To name a few, other applications of the developed technology are: THz scanners for security screening, medical imaging, quality control in agrifood industry (detection of undesired objects or defects), and THz wireless communications, which possess the potential of providing the BW required by future wireless systems. Recent studies estimate that successful deployment of 5G could bring about 146 billion € in annual benefits for automotive, healthcare, transport and utilities industries. In addition, 5G deployment is likely to create 2.39 million jobs in the EU. This project will improve Europe’s capability of offering new solutions for major society challenges. We intend to enable the wide-spread use of THz technology in everyday life, and more traditional applications like radioastronomy and THz security screening. We believe that the proposed technology will be a milestone for the impact which volume-deployable THz technology can have on the society of the future.