Using the long-established Cardiff metal-mesh filter technology, we have exploited our ability to artificially manipulate the phase of a wavefront across a device in order to produce a dielectric-based Toraldo pupil working at millimeter wavelengths. The use of a Toraldo pupil to push the angular resolution of an optical imaging system beyond the classical diffraction limit is yet to be realized in the millimeter regime, but is an exciting prospect. Here we present the design and measured performance of a prototype Toraldo pupil, based on a 5 annuli design.
We present the control system of the 84-116 GHz (3 mm band) Superconductor-Insulator-Superconductor (SIS)
heterodyne receiver to be installed at the Gregorian focus of the Sardinia Radio Telescope (SRT). The control system is
based on a single-board computer from Raspberry, on microcontrollers from Arduino, and on a Python program for
communication between the receiver and the SRT antenna control software, which remotely controls the backshorttuned
SIS mixer, the receiver calibration system and the Local Oscillator (LO) system.
Proc. SPIE. 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII
KEYWORDS: Principal component analysis, Zinc, Fourier transforms, Interference (communication), Field programmable gate arrays, Space telescopes, Signal processing, Galactic astronomy, Signal detection, Stochastic processes
SETI, the Search for ExtraTerrestrial Intelligence, is the search for radio signals emitted by alien civilizations living in the Galaxy. Narrow-band FFT-based approaches have been preferred in SETI, since their computation time only grows like N*lnN, where N is the number of time samples. On the contrary, a wide-band approach based on the Kahrunen-Lo`eve Transform (KLT) algorithm would be preferable, but it would scale like N*N. In this paper, we describe a hardware-software infrastructure based on FPGA boards and GPU-based PCs that circumvents this computation-time problem allowing for a real-time KLT.
In this article, we present the design and performances of the radio receiver system installed at the Sardinia Radio
Telescope (SRT). The three radio receivers planned for the first light of the Sardinian Telescope have been installed in
three of the four possible focus positions. A dual linear polarization coaxial receiver that covers two frequency bands,
the P-band (305-410 MHz) and the L-band (1.3-1.8 GHz) is installed at the primary focus. A mono-feed that covers the
High C-band (5.7-7.7 GHz) is installed at the beam waveguide foci. A multi-beam (seven beams) K-band receiver (18-
26.5 GHz) is installed at the Gregorian focus. Finally, we give an overview about the radio receivers, which under test
and under construction and which are needed for expanding the telescope observing capabilities.
Existing radio receivers have a very low noise temperature. To further increase the observation speed, the new generation
of radio receivers use a multi-beam focal plane array (FPA) together with wide bandwidth. In this article, we present the
front-end and cryogenic design of the 7-beam FPA double linear polarization receiver for the 64-m primary focus of the
Sardinia Radio Telescope. At the end of this article, we show the simulated performances of the front-end receiver and
the measurements of the down-conversion section.
We present the optical and mechanical design of a 3mm band SIS receiver for the Gregorian focus of the Sardinia Radio Telescope (SRT). The receiver, was designed and built at IRAM and deployed on the IRAM for the Plateau de Bure Interferometer antennas until 2006. Following its decommissioning the receiver was purchased by the INAFAstronomical Observatory of Cagliari with the aim to adapt its optics for test of the performance of the new 64-m diameter Sardinia Radio Telescope (SRT) in the 3 mm band (84 – 116 GHz). The instrument will be installed in the rotating turret inside of the Gregorian focal room of SRT. The dimensions of the focal room, the horn position in the lower side of the cryostat and the vessel for the liquid helium impose very hard constraints to the optical and mechanical mounting structure of the receiver inside the cabin. We present the receiver configuration and how we plan to install it on SRT.
A 3mm band focal plane array heterodyne receiver is being developed for Nasmyth focus of the IRAM 30-m Pico Veleta
Radio Telescope located in the Sierra Nevada Mountains, south of Spain. This receiver will comprise 25 dual linear
polarization pixels operating across the 80-116GHz nominal band. Design efforts are being made to enlarge the band to
cover the full 3mm atmospheric transmission window available at Pico Veleta, i.e. 72-116GHz. The instrument will be
coupled to the Pico Veleta Telescope via a purely reflective low-loss optical system that includes a de-rotator. The
receiver will be based on 5 x 5 cryogenically cooled dual-linear polarized feed horns cascaded with Ortho Mode
Transducers (OMT) and side band separating SIS mixers, a technology which offers state-of-the-art performances for
millimeter and sub-millimeter receivers.
We present the design, construction and test results of a prototype MMIC receiver for the 3 mm band (84-116 GHz). The
receiver cryogenic module consists of a single corrugated feed horn cascaded with an Ortho Mode Traducer (OMT) that
splits the two incoming linear polarized signals in two independent single-mode rectangular waveguides. Low noise
MMIC HEMT amplification modules, attached to the OMT WR10 waveguide outputs, amplify the signal of each
polarization channel. Outside the dewar, each signal is filtered, down-converted, and further amplified to provide a final
8 GHz IF bandwidth across 4-12 GHz. The receiver was installed on the Pico Veleta 30 m telescope in August 2010
where it was used to perform spectral line surveys of astronomical sources. The measured receiver noise temperature was
below 75 K with an average value of ~55 K for both polarization channels across 84-116 GHz.
We describe the design construction and performance of a L-band (1300-1800 MHz) Ortho Mode Junction for the L-P
dual-band receiver to be installed on the 64 m Sardinia Radio Telescope (SRT), a new radio telescope which is being
built in Sardinia, Italy. The Ortho Mode Junction (OMJ) separates two orthogonal linearly polarized signals propagating
in a 172 mm diameter circular waveguide and couple them into four coaxial outputs. The OMJ is part of an OMT (Ortho
Mode Transducer), which includes two 180<sup>0</sup> hybrids allowing to recombine the out-of-phase signals from the balanced
OMJ outputs. The OMJ consists of four probes arranged in symmetrical configuration across the circular waveguide. A
shaped tuning stub with cylindrical profile is placed a quarter wavelength away from the probes to guarantee broadband
operation with low reflection coefficient across L-band. The four identical probes have a cylindrical structure, each
consisting of three concentric cylinders that attach to the central pin of standard 50 Ω 7/16-type coaxial connectors. The
OMJ will be cooled at 80 K inside a compact dewar together with directional couplers and Low Noise Amplifiers.
The two linearly polarized signals from an input 190 mm diameter room temperature L-band feed couple into the
cryogenic dewar through a vacuum window located across the waveguide. Inside the dewar, the 190 mm diameter
circular waveguide is tapered down to 172 mm using a conical transition (length 85 mm) filled with a Styrodur® foam
that provides mechanical support for a 0.125 mm thick Kapton vacuum barrier. A 0.6 mm air gap across the 172 mm
circular waveguide provides thermal decoupling between the ambient temperature and the 80 K OMJ, which is
connected to the conical transition output.
We describe the design, construction, and performance of a waveguide Orthomode Transducer (OMT) for the 385-500
GHz band. The OMT is based on a symmetric backward coupling structure with a square waveguide input (0.56x0.56
mm<sup>2</sup>) and two single-mode waveguide outputs: a standard WR2.2 waveguide (0.56x0.28 mm<sup>2</sup>) and an oval waveguide
with full-radius corners. The OMT is rescaled from a lower frequency design that was developed for the 3 mm band; it
was optimized using a commercial 3D electromagnetic simulator.
The OMT consists of two mechanical blocks in split-block configuration, fabricated using a CNC micromilling machine.
A first prototype copper alloy OMT employing standard UG387 flanges at all ports was fabricated and tested. From 385
to 500 GHz the measured input reflection coefficient was less than -10 dB, the isolation between the outputs was less
than -25 dB, the cross polarization was less than -10 dB, and the transmission was ≈-2 dB at room temperature for both
polarization channels. The effects of misalignment errors in the OMT performance were studied using electromagnetic
A second OMT version utilizing custom made mini-flanges and much shorter waveguides was designed and will be
tested soon. This novel OMT is more tolerant to misalignment errors of the block halves and is expected to have much
improved performance over the first prototype.
We present the design of the passive feed system of the dual-band receiver for the prime focus of the Sardinia Radio
Telescope (SRT), a new 64 m diameter radio telescope which is being built in Sardinia, Italy. The feed system operates
simultaneously in P-band (305-410 MHz) and L-band (1300-1800 MHz). The room temperature illuminators are
arranged in coaxial configuration with an inner circular waveguide for L-band (diameter of 19 cm) and an outer coaxial
waveguide for P-band (diameter of 65 cm). Choke flanges are used outside the coaxial section to improve the crosspolarization
performance and the back scattering of the P-band feed. The geometry was optimized for compactness and
high antenna efficiency in both bands using commercial electromagnetic simulators. Four probes arranged in
symmetrical configuration are used in both the P and the L-band feeds to extract dual-linearly polarized signals and to
combine them, through phased-matched coaxial cables, into 180 deg hybrid couplers. A vacuum vessel encloses the two
P-band hybrids and the two L-band hybrids which are cooled, respectively at 15 K and 77 K. For the P-Band, four low
loss coaxial feedthroughs are used to cross the vacuum vessel, while for the L-Band a very low loss large window is
employed. The P-band hybrids are based on a microstrip rat-race design with fractal geometry. The L-band hybrids are
based on an innovative double-ridged waveguide design that also integrates a band-pass filter for Radio Frequency
Interference (RFI) mitigation.
We describe the design, construction and performance of a novel 180° hybrid power divider for L-band (1.3-1.8 GHz).
The hybrid is based on a double ridged waveguide cavity that also integrates a band pass filter. The device will operate at
77 K inside a cryogenically cooled receiver to be installed at the primary focus of the Sardinia Radio Telescope.
The hybrid has three ports consisting of N-type coaxial connectors whose central pins are attached to launching probes
located inside the double ridge waveguide structure. The signal is launched into the cavity from an input probe located
on one cavity end and is extracted from two output probes on the opposite end. The output probes are arranged in
balanced configuration, are axially symmetric, and aligned along the same axis. Both input and output probes are located
in front of reactive loads consisting of shaped tunerless backshorts that provide broad band responses with low reflection
The band pass filter is located in the middle of the cavity, between the two input and output transitions. The dimensions
of the device (excluding connectors) are 70 x 57.2 x 254.4 mm<sup>3</sup>.
The design was optimized using a commercial electromagnetic simulator.
From 1.3-1.8 GHz the measured output reflection coefficient was less than -17dB , the coupling and the phase difference
between inputs and output was respectively, 3±0.25dB and 180<sup>0</sup>±0.9<sup>0</sup>, over the full band. The amplitude and phase
balance performances are much superior to that of commercially available devices.
We describe the design, construction, and characterization results of a waveguide Orthomode Transducer (OMT) for the
3 mm band (84-116 GHz.) The OMT is based on a symmetric backward coupling structure and has a square waveguide
input port (2.54 mm × 2.54 mm) and two single-mode waveguide outputs: a standard WR10 rectangular waveguide (2.54
mm × 1.27 mm,) and an oval waveguide with full-radius corners. The reverse coupling structure is located in the
common square waveguide arm and splits one polarization signal in two opposite rectangular waveguide sidearms using
broadband -3 dB E-plane branch-line hybrid couplers. The device was optimized using a commercial 3D electromagnetic
simulator. The OMT consists of two mechanical blocks fabricated in split-block configuration using conventional CNC
milling machine. From 84 to 116 GHz the measured input reflection coefficient was less than -17 dB, the isolation
between the outputs was less than -50 dB, the cross polarization was less than -30 dB, and the transmission was larger
than -0.35 dB at room temperature for both polarization channels. The device is suitable for scaling to higher frequency.
We present the status of the Sardinia Radio Telescope (SRT) project, a new general purpose, fully steerable 64 m
diameter parabolic radiotelescope capable to operate with high efficiency in the 0.3-116 GHz frequency range. The
instrument is the result of a scientific and technical collaboration among three Structures of the Italian National Institute
for Astrophysics (INAF): the Institute of Radio Astronomy of Bologna, the Cagliari Astronomy Observatory (in
Sardinia,) and the Arcetri Astrophysical Observatory in Florence. Funding agencies are the Italian Ministry of Education
and Scientific Research, the Sardinia Regional Government, and the Italian Space Agency (ASI,) that has recently
rejoined the project. The telescope site is about 35 km North of Cagliari.
The radio telescope has a shaped Gregorian optical configuration with a 7.9 m diameter secondary mirror and
supplementary Beam-WaveGuide (BWG) mirrors. With four possible focal positions (primary, Gregorian, and two
BWGs), SRT will be able to allocate up to 20 remotely controllable receivers. One of the most advanced technical
features of the SRT is the active surface: the primary mirror will be composed by 1008 panels supported by electromechanical
actuators digitally controlled to compensate for gravitational deformations. With the completion of the
foundation on spring 2006 the SRT project entered its final construction phase. This paper reports on the latest advances
on the SRT project.
We describe the design, construction, and characterization results of a compact L-band (1.3-1.8 GHz) Orthomode
Transducer (OMT) for the Sardinia Radio Telescope (SRT), a 64 m diameter telescope which is being built in the
Sardinia island, Italy. The OMT consists of three distinct mechanical parts connected through ultra low loss coaxial
cables: a turnstile junction and two identical 180° hybrid power combiners. The turnstile junction is based on a circular
waveguide input (diameter of 190 mm,) and on four WR650 rectangular waveguide cavities from which the RF signals
are extracted using coaxial probes. The OMT was optimized using a commercial 3D electromagnetic simulator. The
main mechanical part of the turnstile junction was machined out of an Aluminum block whose final external shape is a
cylinder with diameter 450 mm and height 98 mm.
From 1.3 to 1.8 GHz the measured reflection coefficient was less than -22 dB, the isolation between the outputs was less
than -45 dB, and the cross polarization was less than -50 dB for both polarization channels.
We present the design of two 22 GHz tunable bandpass filters based on variable capacitors (in Niobium MEMS technology) realized as short sections of superconductive lines with properties similar to microstrips. The air gap between the top electrode (the microbridge) and the bottom electrode of the thin film Niobium (Nb) microstrips can be varied by ~30% through the electrostatic force generated by a DC bias voltage. Electromagnetic simulation of the two filters predicts a tuning range of ~11% and ~14% of the central filter frequency. One goal of this development is to demonstrate the application of Nb microbridges for variable filters at 22 GHz in view of a transfer to several hundreds of GHz. All steps of the low temperature (<150°C) fabrication procedure are compatible with the fabrication of Nb-Al/AlOx-Nb SIS tunnel diodes, used in heterodyne high frequency mixers operated at 4 K. This fabrication procedure sets limits to the dimensions of the microbridges.
We report on attempts to broaden the IF bandwidth of the BIMA 1mm SIS receivers by cascading fixed tuned double-sideband (DSB) SIS mixers and wideband MMIC IF amplifiers. To obtain the flattest receiver gain across the IF band we tested three schemes for keeping the mixer and amplifier as electrically close as possible. In Receiver I, we connected separate mixer and MMIC modules by a 1" stainless steel SMA elbow. In Receiver II, we integrated mixer and MMIC into a modified BIMA mixer module. In Receiver III, we devised a thermally split block where mixer and MMIC can be maintained at different temperatures in the same module. The best average receiver noise we achieved by combining SIS mixer and MMIC amplifier is 45 -50 K DSB for νLO = 215 - 240 GHz and below 80 K DSB for νLO = 205 - 270 GHz. The receiver noise can be made reasonably flat over the CARMA IF band (νIF = 1 - 5 GHz). Noise temperatures for all three receivers are comparable to or better than those obtained with the BIMA receiver.