The time and frequency standard system for FAST receivers

This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.

Ultra-low noise L-band cryogenic astronomical receiver for the FAST telescope

This paper presents an ultra-low noise L-band radio astronomical cryogenic receiver for the Fivehundred-meter Aperture Spherical radio Telescope(FAST) telescope. The development of key low noise microwave parts of coupling low noise amplifier(Coupling-LNA) and conical quad-ridge orthogonal mode transducers(OMT) and reasonable system integration achieve outstanding performance of receiver. It covers the frequency range of 1.2 GHz to 1.8 GHz. Novel cryogenic Coupling-LNAs with low noise, large return loss, high dynamic range and the function of coupling calibration signals are developed for the proposed receiver. Amplification and coupling function circuits are integrated as a single Coupling-LNA with full noise temperature of 4 K at the physical temperature of 15 K. Its return loss is more than 18 d B, and output1 d B compression power is +5 d Bm. A cryogenic dewar is fabricated to provide 55 K and 15 K cryogenic environment for OMT and Coupling-LNAs, respectively. The receiver's system noise temperature is below9 K referred to feed aperture plane. Benefiting from optimal design and precise mechanical treatment, good scattering performance of OMT and equalized radiation patterns of horn are achieved with an antenna efficiency above 75%.

Development of wideband orthomode transducers for FAST cryogenic receiver system

This paper describes the design,construction,and performance of the wideband orthomode transducers(OMTs)for the L-(1.2–1.8 GHz),the S-(2–3 GHz)and the P-(0.56–1.12 GHz)band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These OMTs operate at the cryogenic temperature of 70 K to reduce their thermal noise contribution to the receiver chains.The development on the FAST L-and S-band quad-ridged waveguide(QRWG)OMTs is carried out based on the theoretical mode analysis.In view of the miniaturization of FAST cryogenic receiver system at P-band,a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength.The proposed L-,S-and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator(HFSS),and then manufactured,tested at room temperature.Measurement of FAST cryogenic receiver system noise is also performed with the L-,S-and P-band OMTs installed.The measured results fully comply with the design specifications.

An Ultra-wide Bandwidth Low-frequency Radio Astronomical Cryogenic Receiver for FAST Telescope

This paper presents an ultra-wide bandwidth(UWB)low-frequency radio astronomical cryogenic receiver for the Five-hundred-meter Aperture Spherical radio Telescope(FAST).It covers 6.6:1 bandwidth from 0.5 to 3.3 GHz.The receiver consists of a Quad-Ridged Flared Horn(QRFH),a cryogenic microwave unit,an optical transceiver and a warm microwave and frequency mixing unit.A QRFH with a concentric-loaded dielectric spear is developed:the average return losses are larger than 20 d B;the average ports polarization isolation is 43.87 d B;the average dish efficiency is higher than 65%.Many UWB cryogenic low loss components are developed for the fabrication of a cryogenic microwave unit.The average noise temperature lower than 14.2 K and 22.5 K are achieved as referred to the input ports of cryogenic Dewar and the output of horn,respectively.Compared to other similar advanced UWB receivers,such as Parkes 0.7-4.2 GHz(6:1 bandwidth)receiver and FAST 0.27-1.62 GHz(6:1 bandwidth)receiver,wider relative bandwidth of the proposed receiver is achieved and it is a new attempt to expand the bandwidth of UWB low-frequency receiver.