The Square Kilometre Array (SKA) Project is a global science and engineering project realizing the next-generation radio telescopes operating in the metre and centimetre wavelengths regions. This paper addresses design concepts of the broadband, exceptionally sensitive receivers and reflector antennas deployed in the SKA1-Mid radio telescope to be located in South Africa. SKA1-Mid (350 MHz – 13.8 GHz with an option for an upper limit of ~24 GHz) will consist of 133 reflector antennas using an unblocked aperture, offset Gregorian configuration with an effective diameter of 15 m. Details on the unblocked aperture Gregorian antennas, low noise front ends and advanced direct digitization receivers, are provided from a system design perspective. The unblocked aperture results in increased aperture efficiency and lower side-lobe levels compared to a traditional on-axis configuration. The low side-lobe level reduces the noise contribution due to ground pick-up but also makes the antenna less susceptible to ground-based RFI sources. The addition of extra shielding on the sub-reflector provides a further reduction of ground pick-up. The optical design of the SKA1-Mid reflector antenna has been tweaked using advanced EM simulation tools in combination with sophisticated models for sky, atmospheric and ground noise contributions. This optimal antenna design in combination with very low noise, partially cryogenic, receivers and wide instantaneous bandwidth provide excellent receiving sensitivity in combination with instrumental flexibility to accommodate a wide range of astronomical observation modes.
The work of this research is the design, analysis and verification of the optical performance of a 4mmreceiver channel
for the 20 m telescope at Onsala Space Observatory, Onsala, Sweden. The 4 mm (75 GHz) receiver is a newly proposed
channel designed to be installed parallel to the existing 3 mm (100 GHz) channel targeting new science at that longer
wavelength. Gaussian beam mode analysis is used to produce the fundamental optical design of the system. The design
is then analysed more accurately with the physical optics approximation. We report on the comparison of simulation
and measurement and verification of the system design.
APEX, the Atacama Pathfinder Experiment, is collaboration between Max Planck Institut fur Radioastronomie (MPIfR) with Astronomisches Institut Ruhr Universitat Bochum, Onsala Space Observatory and the European Southern Observatory (ESO). The telescope was supplied by VERTEX Antennentechnik in Duisburg, Germany, and is a 12 m antenna with 15 μm rms surface accuracy operating at the Atacama Desert Llano Chajnantor, in the Chilean Andes at 5100 m altitude. APEX heterodyne single pixel facility receiver are placed in the telescope Nasmyth cabin A. The receivers are coupled to the antenna via relay optics providing possibility to operate either one of the two different PI-type instruments or a multi-channel facility heterodyne receiver to cover 211 - 1500 GHz frequency range. In this report, we present the optical design for APEX single-pixel facility heterodyne receiver providing frequency independent illumination of the secondary for all the receiver channels. We present design of the two-channel facility receiver APEX A, installed and operating since June 2005, and of the coming 6-channel APEX facility receiver. The report includes a brief review of the mixer technology development status for APEX Band 1, 211 - 270 GHz, using sideband separation technology (2SB), Band 2, 270 - 370 GHz, 2SB, Band 3, 385 - 500 GHz, 2SB, and Band T2, 1250 - 1390 GHz, HEB waveguide balanced mixer, those on the development at Onsala Space Observatory. We present description of the receiver control system and example observation of APEX 2a receiver.
APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.
The Heterodyne Instrument (HIFI) is part of the ESA Herschel Space Observatory Project. The instrument is intended for high-resolution spectroscopy and has a frequency coverage from 480 to 1250 GHz band in five receiver bands and 1410 to 1910 GHz in two additional bands. HIFI is built based on a modular principle: the mixers together with their respective optics are integrated into Mixer Sub-Assemblies (MSA). Each frequency band has two MSAs allocated for horizontal and vertical polarization. In this paper, we present the work done on the design and construction of a Gaussian beam measurement range. One of the unique features of the developed method is a possibility to measure the beam parameters of the MSAs in the absolute coordinate system referred to the device under test. This along with other methods should allow integration of the entire HIFI with the best possible coupling of the antenna beam to the receivers and achieving ultimate performance in such a complicated optical system. The range houses the measured MSA, which is at 4 K ambient temperature, and a continuous wave source placed on a precise scanner entirely under vacuum. Developed triangulation system provides mechanical reference data on the MSA, in-situ, after the entire system is evacuated and the cooling is finished. We adopted a scalar measurement approach where the test source scans the receiver input beam and the mixer IF power is measured. The data collected from 3-4 planar scans are used to calculate the orientation and position of the optical axis. We present results from the first beam measurements for MSA HIFI bands 1 and 2 (480 and 640 GHz), the measurement system performance and accuracy analysis.