G. Serra, F. Gaudiomonte e G.Valente gserra@oa-cagliari.inaf.it
Italian National Institute for Astrophysics Sardinia Radio Telescope Astronomical Observatory of Cagliari
PhD Summer School “Seminario di eccellenza Italo Gorini” Selargius, OAC, September 8, 2016 In the morning 9:30-12:30, at OAC
General talk about radio astronomy and SRT (G. Serra) Introduction to Radio Frequency measurement by Vectorial Network Analyzer (VNA), (G. Valente) Introduction to Radio Frequency Interference (RFI) measurement (F. Gaudiomonte) Labs tour: ◦ VNA calibration and S-parameter measurement of a Low Noise Amplifier (at room temp) ◦ Visit at mechanical shop and electronic/optical laboratory
In the afternoon 4-5:30, at SRT site
◦ a close look at telescope, control room and apparatus box ◦ an experience with the RFI mobile laboratory
Agenda Radio Frequency Measurements for SRT Radio astronomy in a nutshell
◦ System temperature ◦ Antenna temperature ◦ Large reflector antennas ◦ Radio cosmic signals ◦ Receivers noise temperature ◦ Antenna temperature due to atmosphere ◦ Telescope system sensitivity ◦ Frequency bands allocated to radio astronomy service (RAS) ◦ Radio Frequency Interference (RFI) monitoring
Sardinia Radio Telescope Summary
Agenda “Radio astronomy is the study of radio waves originating outside the Earth. The radio range of frequency (ν) ( or wavelength (λ)) is loosely defined by three factors” [see http://www.cv.nrao.edu/course]:
atmospheric transparency quantum thermal noise current technology
“Together they yield a boundary between radio and far-infrared astronomy”:
Upper limit: ν~ 1 THz (1012 Hz) or λ =c/ν ~ 0.3 mm (molecular absorption of the atmosphere) Lower limit: ν~ 50 MHz (107 Hz) or λ =c/ν ~ 6 m (ionosheric refraction) c = speed of light
Radio astronomy in a nutshell The water vapor start affecting the ground based radio astronomical observations above 10 GHz (λ < 3 cm)
Radio astronomy in a nutshell The water vapour (IWV) content is the main limiting factor for ground based radio astronomical observations (at frequency >20 GHz).
Radio astronomy in a nutshell Tsys =TA +Trec [ Kelvin ] Radio telescopes measure the temperature equivalent to the total noise power from all sources referenced to the input of an ideal receiver connected to the output of the antenna.
It is called the system noise temperature (Tsys) and is the sum of antenna temperature (TA) and the receiver noise temperature (Trec) Radio astronomy in a nutshell TA = Tsource +Tcmb + Tatm + Tground
Contributions in the telescope beam from:
• the cosmic microwave background (Tcmb ~ 3 K) • atmospheric emission (Tatm) • ground radiation (Tground ) • astronomical sources (Tsource) being observed
Radio astronomy in a nutshell Planck spectra for a black blody From the Planck’s law which defines the spectral distribution of at different temperature
the radiation Bν of a black body at temperature (T) in thermodynamic equilibrium
in the bounds of the validity of the Rayleigh-Jeans approssimation
hν< Planck’s constant h=6.62*10-34 [m2 kg s-1], frequency ν, Boltzmann’s constant k =1.38*10-23 [Joule / Kelvin ], the brightness Bν and the thermodynamic temperature T of the black body emitting the radiation at ν are proportional. It allows astronomers to infer the brigthness Bν (TB ) of the observed cosmic source by measuring the antenna temparature TA Radio astronomy in a nutshell Therefore, TA can be attained by: TA = ( Aeff/2K ) Sν 2 -2 -1 Aeff telescope effective collecting area [m ] , Sν flux density of the observed source [Watt m Hz ] S ν from a point-like source ν = Ωs B (T) dΩ S from a wide source (constant brightness in the antenna beam) Largeν = ABν Ω A to collect as much T as possible eff a -2 -1 퐁ν source brightness [Watt m Hz steradian], 훀퐬 source solid angle [steradian], 훀 solid angle [steradian], antenna beam solid angle [steradian] 훀퐀 And finally, by a proper calibration large reflector, the received antenna power on the ( highantenna antenna input from again) radio source can be calculated: Pν = K TA Δν = 1/2 * Aeff Δν Sν Note. One-half is due to fact that antenna has a certain polarization (linear, vertical or horizontal, circular, Right or left), but the polarization of noise is random. Therefore one-half of the noise power is in a given polarization. Radio astronomy in a nutshell Green Bank Telescope (D=100m), West Virginia, USA Very Large Array (27 antennas, D=25 m each), Socorro, New Mexico, USA d Single dish antenna Angular resolution θ =1.2 λ/D Interferometer (antenna array) Angular resolution θ ~ λ/d Sardinia Radio Telescope (D =64m), Italy Radio astronomy in a nutshell The radio cosmic signal are very weak. The order of magnitude of a generic radio source flux density Sν is around a unit of Jansky (Jy): 1 Jy = 10-26 [ W m-2 Hz-1 ] The power at the cell phone receiver input due to LTE transmissions (~2 W, G=11 dB @ 2.1 GHz) at 5 km is P = 1.6 * 10-9 W = -88 dBW For a large telescope (as SRT) having 2 Aeff = 2000 m , a total power receiver bandwidth equal to Δν = 1 GHz the power at the telescope receiver input would be: -14 P = 1/2* Aeff Δν Sν = 10 W = -140 dBW More than 5 orders of magnitude greater Radio astronomy in a nutshell MITEQ M89C MA/COM MZ5010C MITEQ AFS207900690-S2 Hot or or RLC DITOM Hittite Minicircuit Minicircuit MiniCircuit Vacuum LNA MITEQ TB440LW1 JCA 48-100 BPF-250-7000-2300-6R D3C6012 HCM129G8 ERA2 ERA6 ADC-2-12 window BPF 6-8 GHz IF Directional LNA FEED Coupler DPS OMT BPF 6-8 GHz z LNA l H a n IF G g i 5 Hot MA/COM MZ5010C MITEQ AFS207900690-S2 RLC DITOM Hittite Minicircuit Minicircuit MiniCircuit . S 6 Cryostat LNA or or BPF-250-7000-2300-6R D3C6012 HCM129G8 ERA2 ERA6 ADC-2-12 2 F MITEQ TB440LW1 JCA 48-100 - R 8 1 푇 , 퐺 Hittite Hittite푇푟푒푐푛, 퐺푛−1 푟푒푐1 1 H407 H407 Printed UMCC UMCC UMCC UMCC UMCC UMCC UMCC UMCC Splitter PS-N000-2S PS-N000-2S PS-N000-2S PS-N000-2S PS-N000-2S PS-N000-2S PS-N000-2S PS-N000-2S Hittite NARDA NARDA Second down-conversion 4316-4 4316-4 H407 printed circuit board UMCC PS-N000-2S Minicircuit Minicircuit ZVA-213-S+ ZVA-213-S+ Hittite UMCC PS-E000-8S MITEQ CMP-010-05900-15P Rohde & Schwarz LO2=5.9 GHz Synt LO1=12-18.5 GHz 1 1 1 푇푟푒푐 = 푇푟푒푐1 + 푇푟푒푐2 + 푇푟푒푐3 + ⋯ + 푇푟푒푐푛 퐺1 퐺1퐺2 퐺1퐺2 … . . 퐺푛−1 K-band receiver Trec =30 K Radio astronomy in a nutshell zenith Radio astronomy in a nutshell 휏 − cos(90−퐸퐿) 퐴푒푓푓 ∝ 퐺 ∝ 푒 antenna gain (G) 휏 − cos(90−퐸퐿) 푇퐴 ∝ 푇푎푚푏 1 − 푒 Noise temperature (TA ) zenith τ = sky opacity [Neper], El = elevation angle [deg] Radio astronomy in a nutshell There is a limit on the measurement of Tsys given by system sensitivity (noise uncertaintly): 1/2 1 Δ퐺 2 Radiometer equation σ푇 ~ 푇푠푦푠 + Δν τ푖푛푡 퐺 Δν receiver bandwidth, τint integration time, ΔG gain instability (fluctuation due to atmosphere emissions). The ideal radiometer equation suggests that the sensitivity of a radio observation improves as 1/2 (1/τint ) , but with a caveat: Δ퐺 1 ≪ 퐺 Δν τ푖푛푡 Radio astronomy in a nutshell In 1959, at the ITU World Radiocommunication Conference: Radio Astronomy was recognized as a “radiocommunication service” creating a legal basis to seek protection against “harmful” interference. A series of frequency bands was allocated to the Radio Astronomy Service. Other bands those allocated to the Space Research Service (2200 – 2300 MHz and 8400 – 8500 MHz) Radio astronomy in a nutshell The RFI groups at italian radio telescope work together to: minimize the Radio Frequency Interference issues keep the protected frequency bands free from RFI monitor the receiver frequency bands to collect information on RFI: like power level, modulation, statistical occupancy, auto-interference Radio astronomy in a nutshell - Single dish operation - Part of VLBI network - Radioastronomy and geodynamical studies - Space Science (Deep Space Communications, Space Surveillance e Tracking) Collaboration among three Research Structures of INAF: • INAF Astronomical Observatory of Cagliari, Cagliari • INAF Institute of Radio Astronomy, Bologna • INAF Arcetri Astrophysical Observatory, Florence SRT milestones: Cost 60 MEuro • In 2013, opening cerimony Main Funding Institutions: • MIUR (Italian• MinistryIn 2015, of end Education of the scientificand Scientific validation Research ) • ASI (Italian Space Agency) • Feb 2016, start of early science observations • RAS (Sardinia Regional Government) Sardinia Radio Telescope Sardinia Radio Telescope SRT technical specifications: Fully steerable antenna Gregorian optical configurations with shaped surfaces Active surfaces primary reflector D=64 m: 1008 panels adjustable by 1116 actuators Active secondary reflector D=7.9 m: 47 panels and 6 electro-mechanical actuators Frequency coverage: 0.3-115 GHz 6 focal positions:primary, gregorian and 4 beam wave guide Can host up to 20 dual-polarizazion receivers Sardinia Radio Telescope At the present SRT is able to observe the sky in the frequency range: 0.3-26 GHz 18-26 GHz 8.2-8.6 /31.85-32.825 GHz 0.3-0.41 /1.3-1.8 GHz receiver receiver X-Ka band receiver band - P/L band band - K 5.7-7.7 GHz Gregorian Focus Forthcoming receivers receiver : • Low-C band: 4.2-5.6 GHz, cryo monofeed dual-circular pol. for BWG f/D=2.81 focus; • Q band band: 33-50 GHz, cryogenic 19-beam dual-circular pol. for Gregorian focus; BWG foci - • SC band: 3.0-4.5 GHz, cryogenic 7-beam dual-linear pol. for primary focus; • W band: 84-116 GHz, cryogenic monofeed single pol. SIS for Gregorian focus; • C band Phased Array Feed: cryogenic, for primary focus Sardinia Radio Telescope Parameter Value Band 305 – 410 MHz 1.3 – 1.8 GHz Polarization Lin. X-Y, Circ. R-L Cryo. temps. 20 K, 77 K Down-conversion No Max dimensions 1.5 x 1.5 x 1.4 m3 Insertion Loss ≤ 0.2 - 0.3 dB Return Loss ≥ 26 dB Cross-polar ≤ -35 dB Edge Taper -12 dB @ 74 deg Sardinia Radio Telescope Testing the L- P Band receiver noise in the lab with cryogenic load and transitions Transitions Test of L band Test of P band Sardinia Radio Telescope Total Power (TP): up to 7 beams dual pol., 2 GHz BW DFB (Digital Filter Bank): 1 GHz BW full-Stokes; up to 2048 ch., folding and search mode (Pulsars); Roach1: 512 MHz BW, sw correlation - CPU cluster (Pulsars); XARCOS: 62.5 MHz, 7 beams dual pol., 2048 ch., freq. res. down to 0.25 KHz (full-stokes spectroscopy); Roach2: 2 GHz BW, 7 beams full-Stokes, f/w: up to 16 kch., (pulsars, spectroscopy, continuum, spectro-polarimetry). VLBI backend: DBBC + MK-V recorder; ROACH DBBC New generation digital backend based on FPGA technology and high-speed ADCs up to 2 GHz signal BW After the first panels alignment of the secondary (in 2010) and primary mirror (in 2012) with fotogrammetry measurement (by SIGMA 3D) Subreflector surface Primary reflector surface Accuracy: ~ 60 μm RMS @ 45° elevation Accuracy: ~ 290 μm RMS @ 45° elevation Overall RMS accuracy of the reflecting surfaces ε~ 310 μm (= λ/20 @ ~ 48 GHz) Very good surface efficiency up to 48 GHz Sardinia Radio Telescope We operate a new Radiometrics MP3000A microwave radiometer with 35 selectable channels, in 22-30 and 51-59 GHz bands. This radiometer is able to provide in real-time IWV, opacity and vertical profiles of temperature, humidity, vapor and liquid content up to 10 km of height. Accuracy in IWV estimate is < 1mm. Good high frequency observations above 20 GHz only with IWV <10 mm (i.e. opacity < 0.1 np) Sardinia Radio Telescope Time e frequency reference for SRT Time Reference to SRT & time keeping Sardinia Radio Telescope Scientific discoveries (papers) 3C129, SRT 6.6 GHz Galaxy cluster Credit:: M. Murgia and al. H2O Maser line at increasing spectral resolutions Credit:: scientific validation team Summary Deep space communication November 2015, SRT received the Rosetta spacecraft signal (X-band) Summary Technological transfer (spin-off) Astronomical Observatory of Cagliari hosts small local company in its laboratories. (Sarda sensor project funded by Regional Governement) Summary file:///C:/Dati/SRTOAC/Divulgazione/2016/ScuolaDottore8Settembre 2016/SRT_Tour360/index.html Thanks for your attention! Any questions?