Abstract
The signal reception chain is an essential element for achieving the square kilometer array-low (SKA-low) system requirements in terms of high sensitivity and dynamic range. The balance between gain, linearity, and low power consumption, as well as the cost, are fundamental parameters that influence the selection of the most suitable technology for SKA-low. Further factors, such as low self-generated radio frequency (RF) interference, high reliability, robustness under extreme environment, and last but not least, the distance between the antennas and the acquisition systems, have impacts on the selection for both architecture and receiver system design. The selected technology for the SKA-low RF signal transportation is RF-over-fiber systems, where the preamplified RF signal picked up by the antennas is carried via analogue modulation over optical fiber. The rationales behind the selection are reported, along with descriptions on the development of the receiver prototypes. The prototypes were deployed and installed on the demonstrator arrays at the selected SKA-low site in Western Australian. Particular attention has been put on the thermal characterization of the receiver system under the actual operating temperature on site, especially when both transmitting part and the optical medium are subjected to external ambient temperature variations. Performance issues encountered in the demonstrator arrays are also discussed along with some proposals for future activities.
Highlights
Analogue radio frequency-over-fiber (RFoF) technology is widely used in various industries from cable television (CATV) and mobile telecommunications to radio astronomy instrumentation
These aspects of the receiver for square kilometer array-low (SKA-low) have been studied through a few consortium projects, such as the Aperture Array Verification Program (AAVP) and the Aperture Array Design Consortium (AADC), where colleagues from different institutions as the Dutch Institute for Radio Astronomy (ASTRON28), the Australian International Centre for Radio Astronomy Research (ICRAR29), the University of Cambridge (UCAM30), the Italian National Institute for Astrophysics (INAF31), and University of Bologna (UNIBO)[32] have analyzed all these specific issues and subsequently verified and improved the RFoF module designed for the prototypes/ demonstrators mentioned in Sec. 1, in particular AAVS1, AAVS2 (see Figs. 4(a) and 4(b), respectively), and EDA2, filling those design gaps found during the field campaign tests
The RFoF technology has been successfully applied to radio astronomy receiving systems for decades
Summary
Analogue radio frequency-over-fiber (RFoF) technology is widely used in various industries from cable television (CATV) and mobile telecommunications to radio astronomy instrumentation. The choice of the optical fiber as transmission channel results to be the only one that allows compliance with the mentioned constraints, and in the final design of SKA-low, the radioastronomical signals coming from 512 array stations each one consisting of 256 double polarization antennas will be connected either to the CPF or to the correspondent RPF through an appropriate RFoF-based link.[2]. The structure of the RFoF receiver to be utilized in SKA-low, which is to date almost completely finalized, is the result of successive design and refinement operations that took place in the latest years thanks to the realization of demonstrator stations Two examples of these SKA-low demonstrators, all deployed at the Murchison Radio-astronomy Observatory (MRO) in the immediate vicinity of the actual SKA-low location, are given by the aperture array verification system and the engineering development array, in their different phases (AAVS1,3 AAVS24 and EDA1,5 EDA2,6 respectively).
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