about me

My humble beginnings

12-meter Greenland Telescope, Thule Air Base, Greenland

As a child I was always fascinated with radio communications and wondered such things worked.  We lived near a small library in the Columbia City portion of Seattle and I quickly went through their collection of books pertaining to radio and TV.  And to the dismay of my parents I was also into disassembling things to figure out how they worked.  Most of my possessions, including my most valued electric train set was never the same again and I still carry some vivid memories of revelations from my experiences at 7 or 8 years old.  

As with most people I knew, I started working part-time jobs from the 9th grade and continued through college where I majored in electrical engineering at UW.  My first engineering job was at Boeing Aerospace in Kent Space Center.  I had no idea what I was getting into and was assigned the task to design an RF circuit board to down-convert and digitize a radio signal from a JTIDS terminal.  It was scary as this was my first exposure to surface mount components and microstrip/stripline designs but fortunately I had a good mentor (GWF).  The engineering process of going from paper design to circuit boards, chassis and racks, then delivering and integrating at a Naval facility in San Diego was intense and at the same time appealing to me.  Like putting together a giant jigsaw puzzle with pieces that you are inventing along the way.  


After Boeing I ended up moving onto TRW in Redondo Beach, California, courtesy of someone I used to work with at Baskin & Robins (on MLK Jr Way So - still there!), while in high school.  It really is who you know.  TRW was a great place to work and I also found Los Angeles to be a fun place to live while in my 20s and 30s.  I worked with a group of modem engineers and we specialized in the development of high data rate satellite ground station receivers. These experiences at Boeing and TRW (now Northrop Grumman) were my formative years as an engineer and played an important part of who I am today. 

Fast forward to halfway through my career, I made a switch to work in astronomy and live in the small town of Hilo, Hawaii. Going from industry to a research organization was a difficult transition for me but I've found that most academic organizations are of the accommodating sort.  I've definitely learned a lot of new things pertaining to astronomy and astronomical techniques that are not a normal part of communications.  And like most things in life, the more I learn the more I know what I don't know.  A big THANKS to the people that have and continue to share their knowledge with me, you know who you are.  I consider myself quite lucky to be doing something that I yearned to do as a child.  

System Design Approach

Partial assembly of ALMA LO Reference Test Module (LORTM)

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 analogous to design by committee and is 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. 

Instrument Designs

Greenland Telescope LO Photonics Receiver assembly

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.  And more often than not, I end up doing the mechanical design and assembly which can often be an integral part of the units thermal and electrical performance.  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 with an eye toward craftsmanship.      

current projects

GLT LO Photonics Transmitter

Greenland Telescope LO Photonics Transmitter assembly

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.  This unit 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.  A big thanks to Ryan for his craftsmanship assembly work.  (D. Kubo, R. Chilson)

GLT LO Photonics Receiver

Greenland Telescope LO Photonics Receiver assembly

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)

GLT Fiber Optics System

Greenland Telescope fiber optic splice chassis with SC/APC I/O connectors

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)

GLT IF Processor

Greenland Telescope IF Processor assembly

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)

GLT Backend Reference

Greenland Telescope Backend Reference assembly

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)

GLT Hardware System Block

Greenland Telescope system block diagram

2019 - 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-0Q, 17th revision. (D. Kubo, C.C. Han, M. Inoue, S. Matsushita, K. Asada)

recent projects

YTLA System Architecture

YTLA system block diagram

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)

YTLA I/Q Down Converter

YTLA I/Q Down Converter assembly

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)

YTLA Noise + Tone Calibration Plate

YTLA Noise/Tone Calibration plate assembly

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)

YTLA Clock Distribution

YTLA Clock Distribution assembly

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)  

SWARM Block Down Converter

SMA Block Down Converter (BDC) assembly

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)


ALMA LO Reference Test Module (LORTM)

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)

1st and 2nd author publications

Electronics Instrumentation for the Greenland Telescope (2018 SPIE conference proceeding)

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. 

Development of Digital Sideband Separating Downconversion for YTLA (2016 SPIE conference proceeding)

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.

Development of a Mach–Zehnder Modulator Photonic Local Oscillator Source (2013 IEEE journal)

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. 

AMiBA Wideband Analog Correlator (2010 Astrophysical Journel)

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. 

Overview of Engineering Activities at the SMA (2008 SPIE conference proceeding)

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.

Characterization of Instrumental Phase Stability (2006 SPIE conference proceeding)

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. 

contact info

Chief Engineer of Hawaii Operations

Research Corporation of the University of Hawaii

Project - Academia Sinica

Institute of Astronomy & Astrophysics


Derek Kubo

645 North Aohoku Place, Hilo, Hawaii 96720, United States

personal research

Carl Sagan books in a big galaxy

Back when I was in high school I read a number of Carl Sagan books that argued for the possibility of other civilizations in existence within our galaxy. And as a young person looking up at the night sky I thought “how could there not be any other sentient beings somewhere out there looking back?” Four decades have passed and we still don’t know how common biological life is in our own solar system, let alone in our galaxy. And if life were to be common elsewhere, how many would develop sentient beings capable of manipulating their environment as we do? These are compelling questions that the science community has only begun to address with our rapidly advancing technology.  


Our milky way galaxy is a big place estimated to be about 100,000 light years across and consisting of about 100 billion stars. If we were to set the detection limit of artificial electromagnetic signals to 5000 light years this radius would encompass around 300 million stars [1]. And, if only one in a million stellar systems develop advanced civilizations the total population in the galaxy will be 100,000 with 300 existing within the detection radius from Earth.  Assuming these numbers are correct, it doesn't sound so unreasonable to expect a detection if we use the correct methodology.  

[1] http://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/LocalGroup/Back/5000lys.html

A long stint in digital communications

During the 1990s I was involved with the design of wide-band (Gbps) digital satellite communication systems 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 convolutional coded for error correction and to maintain balance (50% ones and zeros) and transition densities (no excessively long strings of ones or zeros). And since typical information consists of random 1's and 0's, particularly after encoding, the long integration times typically used in astronomy (i.e. Ti >> Ts, where Ti is integration time in the seconds regime, Ts is transmission symbol time in the usec/psec regime) results in such transmissions to appear as thermal noise indistinguishable from the thermal background.  Though this work did not entail spread spectrum technology it has a similar end result of being difficult to detect at low received power densities.     

Change in detection paradigms and intelligence to fill a niche

In my view as a former communications engineer, I think we should change detection paradigms to search for constant envelop 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 computationally intensive processing).  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 to date.  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 thousands or even millions of times over.  And maybe a shift in detection paradigms is all we need to discover that we are not alone in this big but rather ordinary galaxy.