transforming ideas and concepts into reality
When I was in elementary school my father bought a small crystal AM radio set which fascinated me. How was such a thing possible? We often spent time at the local library in Seattle where I devoured anything related to radio communications. As I got older, this interest never faded and eventually I went to college to study electrical engineering at UW. My first engineering job was at Boeing Aerospace in Kent Space Center where I worked under the tutelage of a great mentor where we developed the RF portion of a set of custom VXI circuit boards for a Navy JTIDS terminal environment simulator. These boards down converted, digitized then reconstructed multiple copies of the original RF signal to produce dynamically varying multi-path interference to emulate a link between a terminal aboard an F18 aircraft and its associated carrier. It was a fascinating introduction to what could be done with electronics. After working at Boeing I had spent 10 years at TRW working with a small team that specialized in the development of high data rate satellite ground station receivers. These experiences at Boeing and TRW were my formative years as an engineer and also played an important role as to who I am as a person. I've since moved onto a career in radio astronomy and find that the technical work is much the same. The big difference from my perspective is that our main focus in academia is the production of science where as in industry the focus was toward providing engineering services for financial profit.
For system designs, I generally concentrate my early efforts working closely with scientists/system engineers toward developing an initial architectural system block diagram. Crude as it may be at this stage, it’s my attempt at laying out hardware solutions for others to scrutinize. From here, trades and compromises are made until we arrive at an architecture that is realizable within the constraints of the project. It’s rarely a smooth process that's full of ambiguity and personalities but if done correctly can make a huge difference on the outcome of a project.
For custom instruments, I typically use a combination of circuit board designs and connectorized RF and/or optical components and integrate into a standalone EMI chassis. My aim is for clean and simple designs that are both functional and aesthetically satisfying to myself and the final end user. I don't consider myself an artist but this is one of my few creative outlets that I spend a lot time thinking through carefully and taking personal pride in.
2019 - This photonics transmitter unit was designed and tested in Hilo and integrated into the system at Thule AB in June. The unit provides optical transmission of 3 signals consisting of 100 MHz maser reference, 15.75 GHz pilot tone, and 18 to 31.5 GHz LO over a wavelength of 1557.2 nm from the maser house to the telescope receiver cabin over a signal fiber and works in conjunction with the photonics receiver unit. The 100 MHz and LO consist of ultra low phase noise references to satisfy VLBI requirements. The 15.75 GHz pilot tone is received in the receiver cabin and retransmitted back to this unit over the same fiber at 1561.1 nm for round trip amplitude and phase measurement. Big thanks for Ryan his craftsmanship assembly work. (D. Kubo, R. Chilson)
2017 - This photonics receiver unit was designed, assembled and tested chiefly by a single individual (said unabashedly of myself) and works in conjunction with a suite of other units within the LO subsystem. Consistent with most development projects, I ran into my fair share of both technical and staffing problems. In order to keep with the tight project schedule I assembled a partially functional prototype transmitter (see Gallery of Work below) for testing of this receiver. With the exception of the round-trip phase monitoring portion, the entire LO subsystem has been deployed and tested at Thule AB in November of 2017 where the telescope currently resides. (D. Kubo, EAO machining)
2017 - Though never a fan of the Just-In-Time (JIT) paradigm in the 90s, here is an example of it. Due to a shortage in our technical staff I ended up designing and ordering the hardware for the fiber system in parallel with working on the LO subsystem. After ordering the fusion equipment, I borrowed a tech from YTLA and flew to San Jose for a 1-day training session a week prior to traveling to Thule AB in September for splicing. Major kudos to Jackie for pulling off the large procurements and to Peter for fusion splicing. I went to Thule in November to install & test the LO subsystem and to complete fiber installations and tests with the terminal equipment. First light for the telescope was obtained a month later in December 2017. (D. Kubo, P. Oshiro, J. Wang, S.H. Chang, ICP)
2017 - Developed the unit requirements for the IF Processor (down converter) and had a technical staff member carry through the detailed work of design, parts procurement, fabrication, assembly and test. Two + 1 spare units were deployed to Thule AB in November of 2017. Kudos to Ryan for the beautiful craftsmanship. (R. Chilson, D. Kubo)
2017 - As part of the LO subsystem, I defined the unit requirements and procured the long lead PLOs for the 2nd LOs (3.85, 8.15 GHz) and clock (2.048 GHz). A technical staff member performed the detailed work of design, parts procurement, fabrication, assembly and test. This unit + 1 spare has been deployed to Thule AB as of November 2017. Kudos again to Ryan for the beautiful work. (R. Chilson, D. Kubo)
2018 - Consistent with my system design approach, I generated the initial system block diagram outlining the electronics architecture for the GLT project. This architecture was based on our existing receiver and backend digital hardware technologies and I developed the Local Oscillator (LO) and Intermediate Frequency (IF) portions in between. A large fraction of this effort involved the design of a system amenable to remote operations and monitoring of phase and amplitude signal stabilities associated to mm-wave VLBI requirements. This diagram has evolved to include several other systems/subsystems including fiber optics, network and computing, calibration, holography and others. A Taipei colleague and I continue to maintain this drawing to reflect the “As Built Configuration” in Thule AB. We are currently on Rev-0P, 17th revision. (D. Kubo, C.C. Han, M. Inoue, S. Matsushita, K. Asada
2016 - As part of an effort to repurpose the AMiBA telescope from a wide-band analog correlator to a digital correlator with higher spectral resolution, I was tasked to develop a microwave design architecture that can digitize any 2 GHz portion of the 2-18 GHz intermediate frequency (IF) band. I was initially struggling with the engineering concept of using switched RF filter banks because of its high cost and reliability issues. Then it dawned on me to use an I/Q down converter similar to my first job at Boeing decades earlier. We hashed out the pros and cons over the next several months and here we are today digitizing any 4 GHz (LSB + USB) portion of the IF band. First light of the full dual polarization system was obtained in April 2018. Major kudos to Ranjani for working on the software and commissioning work. (D. Kubo, C.T. Li, H. Jiang)
2016 - Developed a prototype I/Q down converter and performed astronomical tests to validate this concept. Supervised the design, assembly and test of this production version shown in the above photo, quantity of 14 + 2 spares. This assembly down converts any 4 GHz portion of the 2-18 GHz IF by tuning the LO and maintains decent amplitude balance and quadrature. Residual amplitude and phase correction is performed in the digital domain to maintain >/= 20 dB sideband rejection. The YTLA has completed its commissioning phase and has started early science as of April 2018. Kudos to John for the technical craftsmanship he put into the final production design. (D. Kubo, J. Kuroda, S. Ho, R. Srinivasan, J.C. Cheng, C.T. Li)
2016 - Designed a noise + tone calibration system (covers 2 to 18 GHz) using left over components from the decommissioned analog correlator system. Channel to channel isolation is > 120 dB and was achieved using cascaded SPDT RF switches. As with most things engineering, there was a lot more that went into this design than meets the eye of the casual observer. (D. Kubo)
2015 - Designed and procured parts for for this unit which synthesizes a programmable clock frequency (we currently use 2.24 GHz). Outsourced the assembly and test to our main facility in Taipei. This unit is currently providing the clocks to 16 ROACH-2 chassis at Maunaloa where the YTLA telescope resides. (D. Kubo, C.C. Han)
2013 - Designed and closely oversaw the assembly and test of the first of two sets of BDCs that cover the 8 to 10 GHz portion of the IF spectrum. A second set of 10 to 12 GHz BDCs were leveraged from this design and was constructed, tested & integrated into the system by a technical staff member. Kudos again to Ryan for the beautiful assembly work and to Ranjani for the software. (D. Kubo, R. Chilson, J. Kuroda, R. Srinivasan)
2011 - Designed, assembled and tested this LO Reference Test Module (LORTM) to support the ALMA receiver integration and testing at EA-FEIC in Taichung, Taiwan. A software colleague and I provided onsite support to integrate this unit into their system. This design turned out to be more complicationed than anticipated, click link below to find out more. (D. Kubo, R. Srinivasan, C.C. Han)
GLT - Loading of heavy equipment into receiver cabin, Thule AB, 21-Nov-2017 2:06PM, appears to be night but it's early afternoon (C.C. Han, T.S. Wei)
Abstract - The Greenland Telescope (GLT) project is aiming to participate in the imaging of the supermassive black hole shadow at the center of M87 using Very Long Baseline Interferometry (VLBI) technique. The GLT antenna consists of the 12-m ALMA North American prototype antenna that was modified to withstand extreme weather. This antenna is currently being deployed in Thule Air Base, Greenland, with the eventual destination of Summit Station. In this presentation, we describe the GLT electronics instrumentation including the receiver system, local oscillator references, frequency translators, and digital back-ends, as well as the built-in diagnostic system.
Abstract - This report presents a down-conversion method involving digital sideband separation for the Yuan-Tseh Lee Array (YTLA) to double the processing bandwidth. The receiver consists of a MMIC HEMT LNA front end operating at a wavelength of 3 mm, and sub-harmonic mixers that output signals at intermediate frequencies (IFs) of 2–18 GHz. The sideband separation scheme involves an analog 90° hybrid followed by two mixers that provide down-conversion of the IF signal to a pair of in-phase (I) and quadrature (Q) signals in baseband. The I and Q baseband signals are digitized using 5 Giga sample per second (Gsps) analog-to-digital converters (ADCs). A second hybrid is digitally implemented using field-programmable gate arrays (FPGAs) to produce two sidebands, each with a bandwidth of 1.6 GHz. The 2 x 1.6 GHz band can be tuned to cover any 3.6 GHz window within the aforementioned IF range of the array. Sideband rejection ratios (SRRs) above 20 dB can be obtained across the 3.6 GHz bandwidth by equalizing the power and delay between the I and Q baseband signals. Furthermore, SRRs above 30 dB can be achieved when calibration is applied.
Abstract - This paper describes the development of a photonic local oscillator (LO) source based on a three-stage Mach–Zehnder modulator (MZM) device. The MZM laser synthesizer demonstrates the feasibility of providing the photonic reference LO for the Atacama Large Millimeter Array telescope located in Chile. This MZM approach to generating an LO by RF modulation of a monochromatic optical source provides the merits of wide frequency coverage of 4–130 GHz, tuning speed of about 0.2 s, and residual integrated phase noise performance of 0.3° rms at 100 GHz.
Abstract - A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array for Microwave Background Anisotropy. Lag correlators using analog multipliers provide large bandwidth and moderate frequency resolution. Broadband IF distribution, backend signal processing and control are described. Operating conditions for optimum sensitivity and linearity are discussed. From observations, a large effective bandwidth of around 10 GHz has been shown to provide sufficient sensitivity for detecting cosmic microwave background variations.
Abstract - The Submillmeter Array (SMA) consists of 8 6-meter telescopes on the summit of Mauna Kea. The array has been designed to operate from the summit of Mauna Kea and from 3 remote facilities: Hilo, Hawaii, Cambridge, Massachusetts and Taipei, Taiwan. The SMA provides high-resolution scientific observations in most of the major atmospheric windows from 180 to 700 GHz. Each telescope can house up to 8 receivers in a single cryostat and can operate with one or two receiver bands simultaneously. The array being a fully operational observatory, the demand for science time is extremely high. As a result specific time frames have been set aside during both the day and night for engineering activities. This ensures that the proper amount of time can be spent on maintaining existing equipment or upgrading the system to provide high quality scientific output during nighttime observations. This paper describes the methods employed at the SMA to optimize engineering development of the telescopes and systems such that the time available for scientific observations is not compromised. It will also examine some of the tools used to monitor the SMA during engineering and science observations both at the site and remote facilities.
Abstract - Atmospheric water vapor causes significant undesired phase fluctuations for the SMA interferometer, particularly in its highest frequency observing band of 690 GHz. One proposed solution to this atmospheric effect is to observe simultaneously at two separate frequency bands of 230 and 690 GHz. Although the phase fluctuations have a smaller magnitude at the lower frequency, they can be measured more accurately and on shorter timescales due to the greater sensitivity of the array to celestial point source calibrators at this frequency. In theory, we can measure the atmospheric phase fluctuations in the 230 GHz band, scale them appropriately with frequency, and apply them to the data in 690 band during the post-observation calibration process. The ultimate limit to this atmospheric phase calibration scheme will be set by the instrumental phase stability of the IF and LO systems. We describe the methodology and initial results of the phase stability characterization of the IF and LO systems.
Research Corporation of the University of Hawaii
Project - Academia Sinica
Institute of Astronomy & Astrophysics
645 North Aohoku Place, Hilo, Hawaii 96720, United States
Back when I was in high school I read a number of Carl Sagan books that got me curious about the possibility of other civilizations in existence within our galaxy. As a young person looking up at the night sky, I thought how could there not be any other sentient beings out there looking back? As fascinating and compelling as this question is, I found that most people were either too busy or uninterested in considering the deeper meaning of the question. Imagine how exciting it would be to discover another sentient civilization? Or what if we eventually find out that sentient life is rare, that there are just a handful within our vast galaxy. Would either of these discoveries change the way we think of ourselves as humans?
During the 1990s I was involved with wideband digital satellite communications where we constantly strived toward improving transmitter and receiver data link efficiencies using PSK and QAM modulation formats. These systems put all of the available transmission energy into the information and none wasted on the emission of fix clocks or carriers. The information is typically encrypted then convolutional coded for error correction and to maintain balance (50% ones and zeros) and transition densities (no excessively long strings of ones or zeros). From a detectability perspective it's kind of a catch 22 situation where all of this effort to improve link efficiency also makes the signal appear similar to the noise you are attempting to overcome.
Based on what I know today, if I were to design a deep space interstellar data link I would use a constant envelope PSK modulation format with the attributes described above, and operate at the shortest feasible transmission wavelength (perhaps millimeter to IR) to achieve high spatial directivity. How does this bode for current SETI research programs? I think the answer is “not so well” because the current paradigm is to search for narrowband carriers in the cm wavelength regime.
In my view as a former communications engineer, I think we should search for PSK modulated signals in much shorter wavelength regimes. Granted that this is a very difficult task but there are methods to detect subclasses of PSK in a relatively straight forward manner (not involving KL transforms). This can be done today in the mm wavelength regime but we may have to wait a while for heterodyne technology to come online for IR wavelengths.
The galaxy is a big place and the distances between stellar systems are quite large, 5 light years on average. My gut feel is that simple life in our galaxy is fairly common and might be confirmed indirectly within the next few decades. Intelligence, however, is a separate matter and may indeed be exceedingly rare and would be one explanation for SETI's null results. The flip side might be that intelligence is a natural consequence of competition for resources and, given stable evolutionary conditions, is a niche waiting to be filled by beings like us. After all, it happened once so why couldn't it have happened elsewhere millions of times over. And maybe a shift in detection paradigms is all we need to discover that we are not alone.