In pursuit of advancing large array receiver capabilities and enhancing the 16-element Heterodyne Array Receiver Program (HARP) instrument on the James Clerk Maxwell Telescope (JCMT), we have successfully fabricated 230 GHz finline superconductor-insulator-superconductor (SIS) mixers. These mixers are critical for assessing the potential and prospective for the HARP instrument’s upgrade. Unlike the existing HARP’s mixer, we replace the probe antenna with an end-fire unilateral finline as the waveguide to planar circuit transition. This mixer design is expected to operate from about 160–260 GHz (approximately 47% bandwidth), and the mixer chips’ current-voltage (I-V) curves have been characterized, showing promising results with a quality factor (Rsg/Rn) exceeding 9.3. Evaluation of the double-sideband (DSB) receiver noise temperature (Trx) is currently underway. Once successfully characterised, our immediate aim is to scale the mixer to operate at HARP’s frequency range near 345 GHz to achieve similar broad RF bandwidth performance. Ongoing simulations are currently being conducted for the design of the 345 GHz finline mixer. This work marks a crucial step toward enhancing HARP receiver performance with better sensitivity and wider Intermediate Frequency (IF) bandwidth, enabling higher-frequency observations, and expanding the scientific potential of the JCMT and its collaborative partners.
Auto-Correlation Spectral Imaging System (ACSIS) is an IF, correlation, reduction, and display system for the submillimeter telescope James Clerk Maxwell Telescope (JCMT). It can produce calibrated spectral images in real time and enables rapid imaging of large areas of the sky over a wide spectral range or at high resolution from up to 16 receiver feeds. Now more than 20 years old, the original 8-10GHz synthesizers for the down conversion module are obsolete and no longer available. Due to the hardware changes in the new 4-10GHz model, an interface circuit is needed to shorten the rise time of the serial clock signal. Further upgrades can better support wide IF band 2-12GHz receiver applications, such as Atacama Large Millimeter Array (ALMA) band-6 receivers. This paper discusses the observatory’s development of a new correlator that utilizes several existing electronics to support current and future receivers.
We have fabricated new superconductor-insulator-superconductor (SIS) mixers chips for the 16-element Heterodyne Array Receiver Program (HARP) instrument on the James Clerk Maxwell Telescope (JCMT). The original spare mixer chips were limited and not performed as well as the used ones in HARP. The ability to manufacture new mixer chips would therefore be important for the repair and upgrade of HARP. Our immediate goal is to replace the current nonfunctional mixers in HARP with new chips. We modified the designs of waveguide probe and the matching circuit of the SIS mixer chip. The newly designed chips were fabricated with a quality factor (Rsg/Rn) over 10. The double-sideband (DSB) receiver noise temperature (Trx) is lower than 80K at frequencies between 325 GHz and 375 GHz, which is comparable to the best of the original devices. Three of the sixteen mixers have been replaced and they work very well.
A 345 GHz room-temperature single-pixel heterodyne receiver using sub-harmonic Schottky barrier diode mixers has been installed at the Large Millimeter Telescope (LMT) on the Sierra Negra in Mexico. The receiver was developed at the Science and Technology Facilities Council (STFC) Rutherford Appleton Laboratory (RAL) in the UK in 2013 to perform ground-based atmospheric studies between 312 GHz and 360 GHz. With support from the STFC Global Challenge Research Fund (GCRF) project “Astronomical System Training, Engineering and Collaboration (ASTEC)” the instrument has been reconfigured to support astronomical research and installed on the 50-meter LMT to be used as a pathfinder for sub-millimeter wavelength observations. This new receiver, CHARM (Collaborative Heterodyne Astronomical Receiver for Mexico), has exchanged an originally implemented single-sideband mixer design for a double-sideband device. In addition, a broader bandwidth intermediate frequency (IF) chain, additional digital sampling spectrometers and appropriate interface quasi-optics have been installed. The modifications have resulted in a turnkey receiver system with a double sideband (DSB) receiver noise temperature (Trec) of ~1200 K as measured in the laboratory. The inclusion of a wider IF and a total of four digital spectrometers the instrument encompasses a 12 GHz IF bandwidth with 1.46 MHz resolution. Use of Schottky mixers allows room temperature operation and whilst both of these attributes sacrifice noise performance, and thus detection sensitivity, when compared with cryogenic superconducting systems, they allow a relatively simple system architecture to be implemented that has objective of establishing the LMT sub-millimeter wave performance potential and related quality local atmospheric ‘seeing’ conditions. The detailed design of the instrument, description of the optical system for the LMT adaptation and first-light results are presented.
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