Welcome to Derek's RF/Microwave Design Suite at ASIAA

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)

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.