Abstract
The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, with a one-square-kilometre collecting area. In addition to its ambitious scientific objectives, such as probing cosmic dawn and the cradle of life, the SKA demands several revolutionary technological breakthroughs, such as ultra-high precision synchronisation of the frequency references for thousands of antennas. In this report, with the purpose of application to the SKA, we demonstrate a frequency reference dissemination and synchronisation scheme in which the phase-noise compensation function is applied at the client site. Hence, one central hub can be linked to a large number of client sites, thus forming a star-shaped topology. As a performance test, a 100-MHz reference frequency signal from a hydrogen maser (H-maser) clock is disseminated and recovered at two remote sites. The phase-noise characteristics of the recovered reference frequency signal coincide with those of the H-maser source and satisfy the SKA requirements.
Highlights
Benefiting from innovations in modern atomic clocks, time and frequency have become the physical quantities that can be most accurately and stably measured and controlled[1,2,3,4]
In the case of SKA1, for which hundreds of telescope dishes are planned, a corresponding number of compensation modules would need to be placed at the same central station
We propose and demonstrate a new frequency dissemination and synchronisation method that features phase-noise compensation performed at the client site
Summary
Benefiting from innovations in modern atomic clocks, time and frequency have become the physical quantities that can be most accurately and stably measured and controlled[1,2,3,4]. The frequency stability and phase-noise specifications of the H-maser clock at the SKA central station should be recovered at each dish site. These requirements cannot be well satisfied by current fibre-based frequency dissemination schemes with active compensation. In the case of SKA1, for which hundreds of telescope dishes are planned, a corresponding number of compensation modules would need to be placed at the same central station. This requirement would incur extraordinary space requirements and cause unnecessary complexities and difficulties for future expansion. The proposed scheme can well satisfy all frequency dissemination and synchronisation requirements of the SKA
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