Wideband receivers for the 3-mm band were developed for CARMA, the Combined Array for Research in Millimeterwave
Astronomy. Three cryogenic MMIC (monolithic microwave integrated circuit) amplifiers manufactured in InP 35-
nm technology are combined in a block with waveguide probes and gain equalizers to cover the 80–116 GHz band.
These are followed by a sideband-separating mixer that has two 17 GHZ wide outputs, for upper and lower sidebands.
Each receiver has a feed horn followed by a circular-to-linear polarizer and orthomode transducer. The two polarizations
are amplified by the cryogenic MMICs, and the outputs downconverted in sideband separating mixers, resulting in four
1–18 GHz channels that can be simultaneously correlated. The first receiver was tested in the lab, and on-sky tests
conducted at CARMA. Measured noise temperatures were in the range 40–70 K, with a sideband rejection of about
High angular resolution observations are essential to understand a variety of astrophysical phenomena. The resolution
of millimeter wave interferometers is limited by large and rapid differential atmospheric delay fluctuations.
At the Combined Array for Research in Millimeter-wave Astronomy (CARMA) we have employed a Paired Antenna
Calibration System (C-PACS) for atmospheric phase compensation in the extended array configurations
(up to 2 km baselines). We present a description of C-PACS and its application. We also present successful
atmospheric delay corrections applied to science observations with dramatic improvements in sensitivity and
The Cornell Caltech Atacama Telescope (CCAT) is a 25 m diameter telescope that will operate at wavelengths as short
as 200 microns. CCAT will have active surface control to correct for gravitational and thermal distortions in the
reflector support structure. The accuracy and stability of the reflector panels are critical to meeting the 10 micron
HWFE (half wave front error) for the whole system. A system analysis based upon a versatile generic panel design has
been developed and applied to numerous possible panel configurations. The error analysis includes the manufacturing
errors plus the distortions from gravity, wind and thermal environment. The system performance as a function of panel
size and construction material is presented. A compound panel approach is also described in which the reflecting surface
is provided by tiles mounted on thermally stable and stiff sub-frames. This approach separates the function of providing
an accurate reflecting surface from the requirement for a stable structure that is attached to the reflector support structure
on three computer controlled actuators. The analysis indicates that there are several compound panel configurations that
will easily meet the stringent CCAT requirements.
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) comprises the millimeter-wave antennas of the Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA) Array, and the new Sunyaev-Zel'dovich Array (SZA). CARMA consists of six 10.4-m, nine 6.1-m, and eventually eight 3.5-m diameter antennas on a site at elevation 2200 m in the Inyo Mountains near Bishop, California. The array will be operated by an association that includes the California Institute of Technology and the Universities of California (Berkeley), Chicago, Illinois (Urbana-Champaign), and Maryland. Observations will be supported at wavelengths of 1 cm, 3 mm, and 1.3 mm, on baselines from 5 m to 2 km. The initial correlator will use field programmable gate array (FPGA) technology to provide all single-polarization cross-correlations on two subarrays of 8 and 15 antennas with a total bandwidth of 8 GHz on the sky. The next generation correlator will correlate the full 23-antenna array in both polarizations. CARMA will support student training, technology development, and front-line astronomical research in a wide range of fields including cosmology, galaxy formation and evolution, star and planet formation, stellar evolution, chemistry of the interstellar medium, and within the Solar System, comets, planets, and the Sun. Commissioning of CARMA began in August 2005, after relocation of the antennas to the new site. The first science observations commenced in April 2006.
A new Combined Array for Research in Millimeter-wave Astronomy (CARMA) interferometer is being assembled from the existing Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers and the new Sunyaev?Zeldovich Array (SZA) at Cedar Flat, a site at 2,200 m altitude in the Inyo Mountains east of OVRO. The array will consist of 23 antennas of three different diameters, 3.5, 6.1 and 10.4 m, and will support observations in the 1 cm, 3 mm and 1.3 mm bands. The fist-light correlator is a flexible FPGA based system that will process up to 8 GHz of bandwidth on the sky for two subarrays consisting of 8 and 15 elements. The array configurations will offer antenna spacings from 5 m to 1.9 km allowing unprecedented high resolution and wide field imaging at millimeter wavelengths. Radiometers observing the 22 GHz water vapor emission line will be used to measure and correct for the water vapor induced path delay along the line of sight for each telescope and thereby minimize the time lost to “bad seeing”. This university based facility will emphasize technology development and student training along with leading edge astronomical research in areas ranging from Sunyaev-Zeldovich effect galaxy cluster surveys to studying protoplanetary disks.
The ALMA telescope will be an interferometer of 64 antennas, which will be situated in the Atacama desert in Chile. Each antenna will have receivers that cover the frequencies 30 GHz to 970 GHZ. This frequency range is divided into 10 frequency bands. All of these receiver bands are fitted on a cartridge and cooled, with bands 1 and 2 at 15K and the other 8 are SIS receivers at a temperature of 4K. Each band has a dual polarization receiver. The optics has been designed so that the maximum of the optics is cooled to minimize the noise temperature increase to the receivers.
The design of the optics will be shown for each frequency bands. Test results with the method of testing on a near field amplitude and phase measurement system will be given for the first 4 frequency bands to be used, which are bands 3 (84-116 GHz), 6 (211-275GHz), 7 (275-375 GHz and 9 (600-702 GHz). These measurements will be compared with physical optics calculations.
The Atacama Large Millimeter Array (ALMA), a joint project between Europe and the U.S. and at present in its design and development phase, is a major new ground based telescope facility for millimeter and submillimeter astronomy. Its huge collecting area (7000 m<SUP>2</SUP>), sensitive receivers and location at one of the driest sites on Earth will make it a unique instrument. We present preliminary design concepts for the overall receiver configuration. Optics and cryostat design concepts from OSO, OVRO, RAL, IRAM, NRAO and SRON and their main features are described.