Radio frequency over fiber technology for SKA-low receiver

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.

Optimal Configuration Mitigating Rayleigh-Backscattering-Induced Distortion in Radioastronomic Optical Fiber Systems

“…after the coupler. After propagating in a standard ITU-T G.652 optical fiber of length L = 5 km, which is in the order of the maximum distances covered in SKAlow [6], the signal is detected by photodiode and through a spectrum analyzer the amplitude levels of the spurious tones generated at frequencies 2f RF and f RF + f d are evaluated. Note that this analysis have been performed considering f d = 1 kHz as the lowest value of dithering frequency.…”

“…However the relative variations of the measured quantities can be typically considered as low (e.g.few tenths of dB or less), and, at the same time, on fiber connections of the order of few km length, like the ones considered in this work, they can be appreciated on time scales (e.g. tens of seconds or more) which are much longer than the ones of the phenomena investigated [6].…”

“…In addition to this, while RoF systems for the mobile network are typically designed assuming that at the optical transmitter's side the RF powers of the signals range roughly in an interval of ± few units of dBm, in the case of signals received by radioastronomic antennas these powers can exhibit values of just -60dBm when they come from astronomical sources, while they arrive to a maximum of around -20dBm when they consist in undesired Radio Frequency Interference (RFI) signals coming from satellites, radio and/or television transmitters, etc. [6].…”

Summary on RoF Technologies, Modulations, and Optical Filters: Review

“…Transmits light based on wavelength; it allows light within a specific wavelength range to pass through while blocking light outside that range. Used for long pass and short pass applications, providing selective transmission of light [40].…”

Mutual Coupling Mitigation in Array Dense Regime by an Antenna Distribution Optimization in SKA1‐LOW

“…At the top of the two arms, the antenna feeding lines are connected to two Low Noise Amplifiers (LNAs), one for each polarization. Two coaxial cables, attached to the LNAs' output ports, carry the amplified signal to a Small Modular Aggregation and RFoF Trunk (SMART) Boxes, which is a preconditioning system for filtering, amplifying and converting the signals to the optical domain (Perini et al., 2022). There are 16 SMART‐Boxes in AAVS2.0, while this number will be increased to 24 for the final SKA1‐LOW design.…”