A prototype receiver for Band 2+3 (67-116 GHz) of ALMA.
The privileged geographical situation of Chile has attracted some of the most important astronomical facilities. Among them ALMA excels as the largest radio astronomical facility ever constructed. Although it has just started operation, a key of its long-term success will be to maintain a continuous upgrading program. The three organizations leading the project have already made calls of proposals to determine the new instrumentation that ALMA will host in the next 10 years. One of the most important proposals is to construct heterodyne receivers covering the current Bands 2 and 3 (67-116 GHz). The planned receivers will use ultra-broadband low-noise semiconductor amplifiers in place of the current superconducting mixers. We have started a collaboration with an international consortium to produce such receivers. During the phase A of the project we have produced an optical system able to cover the entire Band. Phase B, starting on March 2016, will produce an entire prototype receiver.
|Optics & OMT for Band 2+3 (Phase A)|
Development of a Prototype for Band 1 (31-45GHz).
The Atacama Large Millimeter Array (ALMA, http://www.almaobservatory.org/) is the largest radio astronomical array ever constructed. Every one of its antennas will cover the spectroscopic window allowed by the atmospheric transmission at the construction site with ten different bands. Despite being declared as a high scientific priority by the ALMA Scientific Advisory Committee, band 1 was not selected for construction during the initial phase of the project. However, Universidad de Chile is running a program for the construction of a prototype receiver for band 1 of ALMA. The first prototype has already been build and tested at cryogenic temperatures.
|ALMA Band 1 prototype|
New receiver for MINI (80-115 GHz)
During the last years, the front end
of the receiver of the MINI has been upgraded in several important
ways. However, the receiver still maintains the double sideband
(DSB) configuration. With the telescope being change to a new site
with lower atmospheric transmission, a new more fundamental upgrading
becomes more import namely using a sideband separating configuration.
This upgrading is important due to the characteristic that 2SB receivers
distinguish between the image and signal sidebands can be exploited
in astronomy by providing enhanced atmospheric noise reduction when
compared with DSB receiving techniques. To complement the front-end
upgrading, we are constructing and integrating a digital correlator
with IF hybridization capabilities.
Simulation of the electromagnetic performance of one of the waveguide components (known as hybrid) necessary to obtain sideband separation. The signal entering the hybrid by the upper right port is divided in signals having equal amplitude but 90° phase difference.
Upgrading of ALMA band-9 receiver (600-720 GHz)
At radio frequencies, the atmospheric
transmission worsens as frequency increases. Therefore, sideband-separating
receivers are preferred at those frequencies. However, above 600
GHz, they have proved to be difficult to construct. With the advent
of new construction techniques, like high-precision CNC machining,
their fabrication is becoming feasible. We have worked, in collaboration
with ALMA Band-9 Group of the Netherlands Institute for Space Research
in developing a new sideband-separating receiver at 600 GHz.
Currently, we are planning to incorporate our sideband-separating digital spectrometer to this receiver.
Close up of part of the waveguide circuit necessary to perform sideband separation. This circuit was machined at our laboratories. Notice that the width of the waveguide is 145 µm. In comparison, a human hair has an average diameter of 100 µm.
A calibrated digital sideband separating spectrometer for radio astronomy applications.
High image rejection receivers are of particular interest at places where the atmospheric noise contribution is high or when radio frequency interference is present. It is also important when the radio source is complex having many/broad spectral lines. Unavoidable gain and phase imbalances strongly limits the achievable sideband rejection ratio of analog instruments to about 10-20dB for high sensitivity, broadband receivers. The increasing power of digital processing hardware has opened the door for a new approach which is based on performing the IF recombination using digital technology. This method allows correcting the amplitude and phase imbalances of the analog front end in the digital back end to achieve high sideband rejection ratios.
We are working in the implementation of a digital sideband separating FFT spectrometer using a FPGA-based platform called the ROACH (Reconfigurable Open Architecture Computing Hardware). The ROACH is developed by the CASPER group (Berkeley). Two ROACH boards were acquired and fitted with Virtex-5 chips thanks to the donation of Xilinx Inc. The results of the research were very positive showing an important improvement with respect to current analog technology. The next step is to test the new spectrometer on the 1.2m mm-wave telescope and to search for new instruments to integrate the technology.
Figure 1: Digital Sideband Separating Spectrometer (DSSM) block diagram.
Figure 2: Millimeter Wave Laboratory Back End area.
Design of an 8-Element Circular Bond-Wire Array Antenna
In the pursuit of higher data
transfer rates for short range wireless communication purposes such
as Wi-Fi and point-to-point networks, the 60 GHz ISM band is expected
to gain popularity in the near future. With shorter wavelengths,
antennas can also be made much smaller. This is leading to new antenna
designs that can be fully integrated with the front-end electronics.
The main two types of integrated antennas are the Antenna on Chip
(AoC) and the Antenna in Package (AiP). A third, hybrid, antenna
model is the Bond-Wire Antenna (BWA), which combines a relatively
high radiation efficiency with excellent integration possibilities.
It does not require an extra transmission line between the front-end
and antenna and furthermore, the BWA can be manufactured using existing
technologies that are already available to chip manufacturers, which
is a tremendous benefit. A circular array of BWA elements can provide
a broad and omnidirectional pattern, with each BWA being very directive.
This makes it excellent for point to point applications, where transmitter
and receiver positions are fixed. This project proposed an array
antenna design that can achieve such a radiation pattern. A prototype
of the BWA array was constructed and tested at the laboratory showing
MINI 115GHz Radio-Telescope
The relocation from Cerro Tololo Observatory to Cerro Calán and an upgrade to the receiver of the MINI radio-telescope is another activity of RAIG. MINI was installed in Cerro Tololo in 1982. A twin MINI telescope is on the roof of -Building D- at the Harvard College Observatory. Together, these two instruments have obtained what is by far the most extensive, uniform, and widely-used Galactic survey of interstellar carbon monoxide (CO), the best general tracer of the largely invisible molecular hydrogen that constitutes most of the mass in molecular clouds. In 2005, the receiver was moved to the Millimeter Wave Laboratory of Cerro Calán to upgrade the Front End and the LO. The 1.2m dish, the dome and the spectrographs were moved in mid-2009 and installed in a new building in mid-2010. First light was obtained on Nov 18, 2010. Regular observations with MINI will start soon. We plan astronomy students to get hands on experience with radio telescopes and electrical engineers to develop technological research. For example, the development of a new digital backend for MINI and the upgrade from DSB to SSB receiver.
|MINI radio-telescope installed in Cerro Tololo in 1982|
ALMA Band 5
ALMA band five covers the frequency window from 163 to 211 GHz including the water line of 183 GHz. The Band 5 receivers are under construction at the Group of Advanced Receiver Development (GARD) on Chalmers University. The first receiver is getting ready for integration at the European Front End integration Center (EuFEIC) in UK, and it will be delivered to ALMA at the beginning of 2011. The Department of Astronomy of the University of Chile (DAS) is part of the consortium for the development of the first 6 receivers providing skilled engineering labor at the EuFEIC and GARD. DAS will be responsible for the integration and verification of the receivers in Chile.
|RF probe for band 5 Beam Scanner Test Source (BeaSTS)|