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 fascination never faded and eventually I went to college to study electrical engineering. My first engineering job was at Boeing Aerospace in Kent Space Center where I worked under the tutelage of a great mentor whom I still attempt to emulate today. We developed an RF circuit board to I/Q down convert and digitize a radio transmission signal from a JTIDS terminal for an environment simulator. This was the beginning of what continues to be a fascinating journey into radio communications and now in radio astronomy.
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 to satisfy the project requirements. 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 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 put a lot of care and detail into these designs as it is a representation of me as a designer. It doesn't always turn out as planned but I'd like to think that I'm getting better with time.
I generated the initial system block diagram outlining the system 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 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-0L, 12th revision. (D. Kubo, C.C. Han, M. Inoue, S. Matsushita, K. Asada)
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. The entire subsystem has been deployed and tested at Thule AB in November of 2017 where the telescope currently resides. (D. Kubo, EAO machining)
Though never a fan of the Just-In-Time (JIT) paradigm in the 90s, here is an example of it. After identifying & ordering a custom fiber cable capable of operation to -65C, I wishfully waited for someone to take the reigns of this system while I worked on the LO hardware. It didn’t happen. I dropped everything to design & purchase dozens of associated hardware along with the fusion splicing equipment, 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. I went to Thule in November to install the LO and complete fiber terminations and tests with the terminal equipment. First light for the telescope was obtained in December 2017. (D. Kubo, P. Oshiro, J. Wang, S.H. Chang, ICP)
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. (R. Chilson, D. Kubo)
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. (R. Chilson, D. Kubo)
Designed a noise + tone injection system for calibration of the SWARM digital correlator. Modified the existing noise distribution system consisting of amplifiers & power dividers to expand the bandwidth from the original 4 to 6 GHz to the current 4 to 18 GHz. (D. Kubo, J. Kuroda, P. Yamaguchi)
As part of an effort to repurpose the AMiBA telescope from a wide-band analog correlator to a digital correlator, I was tasked to develop a system architecture that can digitize any 2 GHz portion of the 2-18 GHz intermediate frequency (IF) band. I was initially struggling with the 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 portion of the IF band. (D. Kubo, C.T. Li, H. Jiang)
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. The YTLA has completed its commissioning phase and has started early science as of April 2018. (D. Kubo, J. Kuroda, S. Ho, R. Srinivasan, J.C. Cheng, C.T. Li)
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. (D. Kubo)
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)
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. (D. Kubo, R. Chilson, J. Kuroda, R. Srinivasan)
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. (D. Kubo, R. Srinivasan, C.C. Han)
GLT - Loading of Heavy Equipment into Receiver Cabin, Thule AB
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 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 - 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.