1.6 GHz Low-Power Cross-Correlator System Enabling Geostationary Earth Orbit Aperture Synthesis

We present a 64-channel cross-correlator system for space-borne synthetic aperture imaging. Two different types of ASICs were developed to fit into this system: An 8-channel comparator ASIC implemented in a 130 nm SiGe BiCMOS process technology performs A/D conversion, while a single 64-channel digital cross-correlator ASIC implemented in a 65 nm CMOS process performs the signal processing. The digital ASIC handles 2016 cross-correlations at up to 3.6 GS/s and has a power dissipation of only 0.13 mW/correlation/GHz at a supply voltage of 1 V. The comparator ASIC can handle sample rates of at least 4.5 GS/s with a power dissipation of 47 mW/channel or 1 GS/s with a power dissipation of 17 mW/channel. The assembled system consists of a single board measuring a mere 136 x 136 mm(2) and weighing only 135 g. The assembled system demonstrates crosstalk of 0.04% between neighboring channels and stability of 800 s. We provide ASIC and system-board measurement results that demonstrate that aperture synthesis can be a viable approach for Earth observation from a geostationary Earth orbit

Cross-Correlator Implementations Enabling Aperture Synthesis for Geostationary-Based Remote Sensing

An ever-increasing demand for weather prediction and high climate modelling accuracy drives the need for better atmospheric data collection. These demands include better spatial and temporal coverage of mainly humidity and temperature distributions in the atmosphere. A new type of remote sensing satellite technology is emerging, originating in the field of radio astronomy where telescope aperture upscaling could not keep up with the increasing demand for higher resolution. Aperture synthesis imaging takes an array of receivers and emulates apertures extending way beyond what is possible with any single antenna. In the field of Earth remote sensing, the same idea could be used to construct satellites observing in the microwave region at a high resolution with foldable antenna arrays. If placed in a geostationary orbit, these could produce images with high temporal resolution, however, such altitudes make the resolution requirement and, hence, signal processing very demanding. The relentless development in miniaturization of integrated circuits has in recent years made the concept of high resolution aperture synthesis imaging aboard a satellite platform viable.The work presented in this thesis addresses the challenge of performing the vital signal processing required aboard an aperture synthesis imager; namely the cross-correlation. A number of factors make the application challenging; the very restrictive power budgets of satellites, the immense amount of signal processing required for larger arrays, and the environmental aspects of in-space operation. The design, fabrication and evaluation of two cross-correlator application-specific integrated circuits (ASICs), one analog-to-digital converter (ADC) ASIC and one complete cross-correlator back-end is presented. Design concepts such as clocking schemes, data routing and reconfigurable accuracy for the cross-correlators and offset compensation and interfacing of the ADCs are explained. The underlying reasons for design choices as well as ASIC design and testing methodologies are described. The ASICs are put into their proper context as part of an interferometer system, and some different cross-correlator back-end architectures are explored.The result from this work is a very power-efficient, high-performance way of constructing cross-correlators which clearly demonstrates the viability of space-borne microwave imaging interferometer back-ends

Correlators for Interferometric Radiometry in Remote Sensing Applications, A Scaling Perspective

Correlators are extensively used in the field of radio interferometry. Two different types are considered for two applications; autocorrelators for spectrometry and cross-correlators for aperture synthesis. We concentrate on satellite-based applications where power budgets are very restrictive. Several satellites are already employing correlators for interferometric measurements, and future projects are targeting even larger systems in terms of spectral channels in the case of spectrometry and baseline counts in the case of aperture synthesis. Thus, it is important to develop correlators with increasing channel count, either using ASIC technology scaling or by constructing larger systems from several ASICs. Building on earlier ASIC designs, we examine how larger correlator systems can be constructed and the implications this has, in terms of power dissipation, system complexity, and ASIC count. Our findings indicate that, for large systems, having a very high channel count per ASIC is indeed of interest for keeping system complexity and power dissipation down by reducing both ASIC and I/O count, especially for cross-correlators

Indoor Full-Body Security Screening: Radiometric Microwave Imaging Phenomenology and Polarimetric Scene Simulation

The paper discusses the scene simulation of radiometric imagers and its use to illustrate the phenomenology of full-body screening of people for weapons and threats concealed under clothing. The aperture synthesis technique is introduced as this offers benefits of wide field-of-views and large depths-of-fields in a system that is potentially conformally deployable in the confined spaces of building entrances and at airport departure lounges. The technique offers a non-invasive, non-cooperative screening capability to scrutinize all human body surfaces for illegal items. However, for indoor operation, the realization of this capability is challenging due to the low radiation temperature contrasts in imagery. The contrast is quantified using a polarimetric radiometric layer model of the clothed human subject concealing threats. A radiation frequency of 20 GHz was chosen for the simulation as system component costs here are relatively low and the attainable half-wavelength spatial resolution of 7.5 mm is sufficient for screening. The contrasts against the human body of the threat materials of metal, zirconia ceramic, carbon fiber, nitrogen-based energetic materials, yellow beeswax, and water were calculated to be ≤7 K. Furthermore, the model indicates how some threats frequency modulate the radiation temperatures by ~ ±1 K. These results are confirmed by experiments using a radiometer measuring left-hand circularly polarized radiation. It is also shown using scene simulation how circularly polarized radiation has benefits for reducing false alarms and how threat objects appear in canyon regions of the body, such as between the legs and in the armpits

SSTAC/ARTS review of the draft Integrated Technology Plan (ITP). Volume 8: Aerothermodynamics Automation and Robotics (A/R) systems sensors, high-temperature superconductivity

Viewgraphs of briefings presented at the SSTAC/ARTS review of the draft Integrated Technology Plan (ITP) on aerothermodynamics, automation and robotics systems, sensors, and high-temperature superconductivity are included. Topics covered include: aerothermodynamics; aerobraking; aeroassist flight experiment; entry technology for probes and penetrators; automation and robotics; artificial intelligence; NASA telerobotics program; planetary rover program; science sensor technology; direct detector; submillimeter sensors; laser sensors; passive microwave sensing; active microwave sensing; sensor electronics; sensor optics; coolers and cryogenics; and high temperature superconductivity

Personal Access Satellite System (PASS) study. Fiscal year 1989 results

The Jet Propulsion Laboratory is exploring the potential and feasibility of a personal access satellite system (PASS) that will offer the user greater freedom and mobility than existing or currently planned communications systems. Studies performed in prior years resulted in a strawman design and the identification of technologies that are critical to the successful implementation of PASS. The study efforts in FY-89 were directed towards alternative design options with the objective of either improving the system performance or alleviating the constraints on the user terminal. The various design options and system issues studied this year and the results of the study are presented

The science case and challenges of space-borne sub-millimeter interferometry

Ultra-high angular resolution in astronomy has always been an important vehicle for making fundamental discoveries. Recent results in direct imaging of the vicinity of the supermassive black hole in the nucleus of the radio galaxy M87 by the millimeter VLBI system Event Horizon Telescope and various pioneering results of the Space VLBI mission RadioAstron provided new momentum in high angular resolution astrophysics. In both mentioned cases, the angular resolution reached the values of about 10–20 microarcseconds (0.05–0.1 nanoradian). Further developments towards at least an order of magnitude “sharper” values, at the level of 1 microarcsecond are dictated by the needs of advanced astrophysical studies. The paper emphasis that these higher values can only be achieved by placing millimeter and submillimeter wavelength interferometric systems in space. A concept of such the system, called Terahertz Exploration and Zooming-in for Astrophysics, has been proposed in the framework of the ESA Call for White Papers for the Voyage 2050 long term plan in 2019. In the current paper we present new science objectives for such the concept based on recent results in studies of active galactic nuclei and supermassive black holes. We also discuss several approaches for addressing technological challenges of creating a millimeter/sub-millimeter wavelength interferometric system in space. In particular, we consider a novel configuration of a space-borne millimeter/sub-millimeter antenna which might resolve several bottlenecks in creating large precise mechanical structures. The paper also presents an overview of prospective space-qualified technologies of low-noise analogue front-end instrumentation for millimeter/sub-millimeter telescopes. Data handling and processing instrumentation is another key technological component of a sub-millimeter Space VLBI system. Requirements and possible implementation options for this instrumentation are described as an extrapolation of the current state-of-the-art Earth-based VLBI data transport and processing instrumentation. The paper also briefly discusses approaches to the interferometric baseline state vector determination and synchronisation and heterodyning system. The technology-oriented sections of the paper do not aim at presenting a complete set of technological solutions for sub-millimeter (terahertz) space-borne interferometers. Rather, in combination with the original ESA Voyage 2050 White Paper, it sharpens the case for the next generation microarcsecond-level imaging instruments and provides starting points for further in-depth technology trade-off studies.</p