Heterodyne Receivers

Transcription

1 Heterodyne Receivers Introduction to heterodyne receivers for mm-wave radio astronomy 7 th 30-m Summer School September 15 th, 2013 Alessandro Navarrini IRAM, Grenoble, France

2 Outline Introduction to Heterodyne receiver and technologies Noise temperature Transmission lines Feeds and Gaussian beam propagation Low Noise Amplifiers (LNAs) SIS mixers Polarization splitters Vacuum windows and IR filters EMIR receiver - Cryogenic system - Local Oscillator system - Cryogenic modules ALMA receiver Array receivers Part 1 Part 2

3 Geometry of the IRAM 30 m telescope optics Secondary focus

4 Heterodyne receivers in short Radiation collected by the telescope is focused onto a feed horn that couples it into a waveguide The heterodyne receiver amplifies and converts some frequency range of the incoming RF signals to a lower frequency IF (Intermediate Frequency) that is sent to the control building

5 Heterodyne receivers and Bolometers Heterodyne Receivers Coherent Frequency conversion from RF to IF using a non-linear device (mixer) Phase information is preserved used in single-dish telescopes and interferometers Spectral information is preserved: very high spectral resolution Used from the cm to the sub-mm region of the spectrum (few GHz to ~THz) Operate at ~4K or ~15 K depending on technology (see later) Bolometers Incoherent Absorbed photon increases temperature, changes resistance Phase information is lost used on single-dish antennas Large bandwidths and high sensitivities Total power detection: spectral information is lost Used for the mm and sub-mm region of the spectrum (~100 GHz to ~THz) Operate at ~0.3 K

6 Power density Heterodyne frequency (down)-conversion by mixing - Signal (RF), RF - Local Oscillator (LO), LO - Intermediate (beat) frequency (IF), IF RF signal at frequency RF Non-linear device (mixer) IF at frequency IF << RF, LO LO at frequency LO IF = RF - LO IF Band DSB mixer: Two sidebands, LSB and USB LO DSB=Double Side Band LSB=Lower Side Band USB=Upper Side Band IF LSB USB IF LSB LO USB Frequency

7 IF signal transport (coaxial cables or fibers) Roles of a heterodyne receiver The main roles of a heterodyne receiver are to collect efficiently the RF astronomical signal concentrated by the antenna near its focal point and to amplify and convert it, by adding as little noise as possible, to a frequency range (IF) and power level suitable for further processing by spectrometers or continuum detectors Antenna Spectrometer Heterodyne Receiver Very weak RF input signals (~10-15 W) Freq Hz (100 GHz) Gain~120 db Frequency down-conversion Low added noise Power level of order few mw; Freq. few GHz

8 Active component technologies for heterodyne receivers HEMT amplifiers (High Electron Mobility Transistors) Direct amplification From few GHz to 115 GHz on telescopes; beyond 500 GHz in the lab Instantaneous bandwidth > 30% Cooled at ~15 K SIS mixers (Superconductor-Insulator-Superconductor) Heterodyne mixing From ~100 GHz to 700GHz (Nb); >1THz (NbTiN) Instantaeneous bandwidth 2 x 8 GHz Cooled at ~4 K HEB mixers (Hot Electron Bolometer) Heterodyne mixing Up to several THz Instantaeneous bandwidth ~ 4 GHz Cooled at ~4 K Schottky diode mixers Heterodyne mixing (fundamental or subharmonic mixing) From few GHz to few THz Broad instantaeneous bandwidth (>100 GHz for mixers operating at few THz) Can operate at room temperature (space application)

9 Synoptic diagram of heterodyne receivers (basic building blocks) cm-wave receiver : first amplify, then down-convert RF < 115 GHz Feed Low noise amplifier LO Schottky mixer IF amplifier IF output Noise critical! mm and submm-wave receiver: first down-convert, then amplify 80 GHz< RF <1.2 THz Feed LO SIS mixer IF HEMT amplifier IF output

10 SIS mixer requires cooling at 4 K; HEMT amplifier can operate at 15 K. The active devices are located inside a cryostat: Feed LSB: GHz Coupler IF: 4-12 GHz LO: 240 GHz LO system

11 SIS mixer require cooling at 4 K; HEMT amplifier can operate at 15 K The active devices are located inside a cryostat Feed LSB: GHz Coupler IF: 4-12 GHz LO system

12 The IRAM 30 m telescope receiver cabin (Pico Veleta, Spain)

13

14 T IN P out =k B B G (T IN +T N ) B=Bandwidth G=Gain T IN =Input signal (R-J approx.) T N =Noise temperature T N For example, a measure with input blackbody at 290 K (room temperature) and 77K (LN 2 ) gives Y = 3 => T N 30 K Blackbodies are available (Eccosorb) at mm and sub-mm wavelengths Advantages of Y-factor method: Requires no knowledge of G and bandwidth Only linear detectors required Fast and reasonably accurate

15 Quantum limit for the noise Irrespective of the technical progress, the system noise temperature has a fundamental quantum limit: T Q =h /k B 5 K ( /100 GHz) Receivers across the mm-wave domain achieve noise performances of only few times the quantum limit

16 Noise temperature of a cascade of stages For a cascade of stages with gain G i >>1, the noise of the first stage T N1 dominates the overall noise temperature. If the first stage has loss (G 1 =1/L 1 <1) or little gain, the noise temperature of the subsequent stage can become important. This is the case of SIS mixers, whose gain is of order 1 or lower. Noise temperature of an attenuator with attenuation L and physical temperature T phys : T N =T phys (L-1) Cooling the low loss optics and the waveguide components (feed, OMT) in front of the active devices reduces the receiver noise temperature.

17 Transmission lines 1/5

18 Waveguides 2/5

19 Rectangular waveguide 3/5 c TE mn modes: E z = 0, H z 0 TM mn modes: E z 0, H z = 0 2, mn 2 m n a b TE 10 is the fundamental mode with cut-off wavelength c,10 =2 a Single-mode operation when: a < < 2 a c/2a < < c/a 2 Example: WR10 waveguide: size 2.54x1.27 mm 2 Single TE 10 mode operation: 59 GHz < < 118 GHz Recommended band: 75 GHz < < 110 GHz (~40% relative band)

20 Rectangular waveguide 4/5

21 Circular waveguide 5/5 The dominant mode is the TE 11 with cut-off wavelength c 11 2πa where a is the circular waveguide radius. Two independent degenerate TE 11 modes can propagate in circular waveguide, which can be associated to two independent polarization modes

22 Electromagnetic modeling softwares A number of powerful commercial electromagnetic softwares are available for accurate modelling of 2D (planar circuitry) and 3D (waveguide and antenna structures). Fast computers are required to perform optimizations on a large parameter space. Mechanical modeling CADs have also a primary importance for the receiver designer.

23 Types of feed 1/6 Planar feeds Waveguide horns

24 Planar feeds 2/6 Broadband (not limited by waveguide cut-off) Lower illumination efficiency than waveguide horns

25 Waveguide feeds 3/6

26 Corrugated feeds 4/6 Properties: - Circularly symmetric pattern - Low sidelobes - Low cross-pol - ~40% relative bandwidth - Low reflection coefficient Variants: - Diffraction limited - Wideband - Profiled - Dual-band Fundamental mode of corrugated waveguide

27 Dual-polarization feed E-field Pol H E-field Pol V Single-polarization feeds E-field E-field 5/6 E-field Pol H Two orthogonal TE 11 modes in circ. waveguide E-field Pol V E-field Single TE 10 mode in rect. waveguide couples to one TE 11 mode in circ. waveguide E-field Waveguide twist

28 Corrugated feeds 6/6 A scalar, or corrugated feed-horn, generates an electric field with almost perfect Gaussian distribution at its aperture. 98% of the power radiated (or received) by the conical corrugated feed is in the fundamental Gaussian mode Corrugated feed-horn for the 2 mm band ( GHz) of the 30 m telescope C-band ( GHz) feed-horn for the beam waveguide focus of SRT Physical dimensions of passive components scale approximately with operating wavelength high frequency small size low frequency big size

29 Fundamental Gaussian beam propagation 1/5 Radius of curvature Beam radius (radius at which the fields falls to 1/e relative to its on-axis value) Power density distribution

30 Antenna efficiency 2/5 Edge Taper Te: relative power density at radius r e

31 Image feed aperture onto telescope secondary mirror 3/5 A relay optics is typically used to image the horn aperture on the telescope s aperture. This fulfils the condition of frequency-independent illumination of the dish.

32 Re-imaging the subreflector into the feed-horn aperture with one or two reflective focusing elements (curved mirrors ) 4/5

33 Focal plane fields: truncation 5/5

34 HEMT low noise amplifiers (LNA) 1/3 Discrete transistors In HEMT (but not in FET), current travels through very pure layer. Two types: MMIC

35 Cryogenic IF Low Noise Amplifier used in ALMA Band 7 (CAY, Spain) 2/3 0.1x150 µm HRL InP transistor

36 MMIC low noise amplifier for the 3 mm band ( GHz) packaged at IRAM 3/3 Metamorphic technology from IAF

37 Superconductor-Insulator-Superoconductor mixers Nb/AlO x /Nb (SIS mixers) Superconductor: Niobium (Nb) AlO x barrier thickness 1 nm, junction area 1 m 2 Working temperature 4 K 1/11 Two kinds of particles exist in a superconductor: Quasiparticles Cooper pairs The tunneling of quasiparticles through the insulating barrier is responsible of SIS mixer operation. The effect is named photon-assisted tunneling. The tunneling of Cooper pairs is responsible of Josephson currents and prevents the good functioning of the SIS mixers. Josephson currents are suppressed using magnetic fields. SIS mixing theory by Tucker is the tool to design SIS mixers.

38 I 0 [ma] I 0 [ma] SIS mixers 0,25 2/11 0,20 0,15 V gap =2 /e 0,10 0,05 0, V 0 [mv] 0,25 LO = 300 GHz 0,20 v LO = h LO /e = 1.24 mv 0,15 = e v LO / h LO = 1 0,10 0,05 0,00 h LO /e h LO /e LO on LO off V 0 [mv]

39 Waveguide SIS mixers 3/ GHz mixer SIS junctions located on a quartz substrate; Waveguide probe couples the signal into the SIS junction(s), usually through supercond. microstrip and/or coplanar waveguides ; Mixer chip is embedded in a waveguide structure machined in a mechanical block The junction capacitance (Cj~75 ff/um2) is tuned out by on-chip superconducting circuitry IRAM mixer chip used in ALMA Band 7, PdBI Band 4, and EMIR Band 4 ( GHz) SIS junctions Chip size: 0.08x0.25x2 mm 3

40 Main SIS mixer types: DSB, SSB and 2SB 4/11 Double Side Band (DSB): Both the USB and the LSB are converted and superimposed on each other at the IF. Single Side Band (SSB): Either the USB or the LSB is down-converted to IF, i.e. one sideband is rejected. Sideband rejection can be achieved through: - Sideband Filter - Mechanically tunable backshort Sideband Separating (2SB): Both sidebands converted and separated to two different IF outputs.

41 Why image rejection, i.e. SSB or 2SBmixer? 5/11 Eliminate this and reduce T SYS, SSB T SYS, SSB 1 GS ( Tout TIF ) T in T in G G I S e F A eff Receiver contribution Signal band Image band G S, G I : Signal and Image Gain; T out : Mixer noise temperature referred to its output; T IF : Noise temperature of the IF amplifier; e -A : Atmospheric transmission factor; F eff : Forward efficiency; Atmosphere + spillover + optics

42 SSB, DSB or 2SB? 6/11 SSB: - Lower spectral confusion; - Rejects atmospheric noise in the image sideband; DSB: -Twice as much as spectral data (if care is taken); - Twice as much continuum power; - Receiver has fewer components - less complexity; 2SB: -Best of both worlds! Requires twice the processing capabilities of SSB and DSB schemes (two IF bands per polarization);

43 SIS mixer types: DSB, SSB and 2SB 7/11 Double Side Band (DSB): Both the USB and the LSB are downconverted and superimposed on each other at the IF: LSB f LO USB IF band Single Side Band (SSB): Either the USB or the LSB is downconverted to IF, i.e. one sideband is rejectd. Sideband rejection achieved (at Iram) by mechanically tunable backshort: Example of LSB tuning (USB is rejected) LSB f LO USB IF band

44 SSB SIS mixer currently installed in EMIR and PdBI Band 2 receivers RF band: GHz (2 mm band); IF Band: 4-8 GHz 8/11 It will be replaced this week in EMIR by a 2SB mixer

45 SIS mixer types: DSB, SSB and 2SB 9/11 Sideband Separating mixer (2SB): Both sidebands (USB and LSB) downconverted and separated to independent outputs 2SB mixer diagram DSB mixer 1 RF input load o RF 90 hybrid coupler In-phase LO coupler LO input load o IF 90 hybrid coupler USB LSB LSB f LO USB DSB mixer 2 IF band IF band ALMA Band 7 2SB mixer ( GHz) SIS mixers currently installed on IRAM receivers are SSB and 2SB (no DSB).

46 EMIR Band 3 ( GHz) 2SB SIS mixer 10/11 LO input SIS mixer chips LO splitter IF1 IF2 RF coupler Signal input (from feed) LO couplers Signal input

47 EMIR Band 3 ( GHz) 2SB SIS mixer 11/11 tuning circuit SIS junction waveguide probe contact pads

48 Polarization splitters 1/2 Wire grid OMT (OrthoMode Transducer) Pol 2 Pol 1 Modified Turnstile junction E-plane bend E-plane power combiner Pol 2 Pol 1

49 Polarization splitters 2/2 Wire grid OMT Advantages: - Compact; - Only one feed-horn required; - Perfect alignment in the sky for the two polarizations;

50 Example of specifications of OMT for the 3 mm band (same as ALMA Band 3)

51 Wire cut of aluminium mandrel Design and fabrication process of OMT for the 3 mm band recently developed at IRAM

52 OMT manufacturing steps

53 IRAM mm-wave Vector Network Analyzer (VNA) Allows S-parameter measurements across IRAM receiver bands Used for characterization of OMTs, waveguide couplers, feed-horn, etc..

54 Characterization of OMT with mm-wave VNA

55 Vacuum windows and IR filters 1/4

56 Vacuum windows and IR filters 2/4

57 Matching grooves have orthogonal directions on the two surfaces. 3/4

58 (example: 3 mm band) 4/4

59 EMIR: Multi-band mm-wave SIS receiver for IRAM 30 m telescope 1/11

60 Cryogenic system of EMIR receiver and of PdBI (and future NOEMA) receivers 2/11 Sumitomo cryocooler SRDK3ST- Closed cycle system Air cooled Compressor CSA71A 3 stages coldhead 77K, 15K & 4K Cooling powers: 33W@77K, 2W@15K, 1W@4.2K 60cm

61 Dewars of EMIR and PdBI receivers 3/11 Dewar and shields: supplied by SNLS, France; Flexible thermal links at each stage to prevent vibration; IF LNA amplifiers and optics modules in thermal contact with 15 K plate; OFHC copper straps at 4K for couplers, SIS mixers and isolators; Cool down time: around 30 hours;

62 4/11

63 New EMIR Band 2 ( GHz) cold optics module (to be installed this week) 5/11 Fiberglass tab (G11) for thermal split View 1 View 15 K Feeds and wire 4 K Ellipsoidal 15 K Polarization splitting 4 K Fiberglass tab (G11) - thermal split

64 New EMIR Band 2 ( GHz) cold optics module including the two 2SB SIS mixers and the waveguide LO splitter 6/11 2SB mixer Pol H IF outputs Corrugated feed-horn Polarization Splitting wire-grid 2SB mixer Pol V LO in IF outputs LO splitter (one LO pumps two polar. channels)

65 Local Oscillator (LO) types Based on fundamental source (up to ~150 GHz) cascaded by frequency multipliers to generate the final frequency (from ~150 GHz to up to beyond few THz) Fundamental sources: 1) Gunn: Solid state oscillator (InP or GaAs), negative resistance coupled to a resonant cavity. Operate in second harmonic mode. Frequencies up to ~150 GHz. Output power >10 dbm (>10 mw). Mechanically tuned. 2) YIG+AMC: - YIG (Yittrium Iron Garnet oscillator): a ferrite material that resonates at microwave frequencies when immersed in a DC magnetic field B. The resonance is proportional to the strength of B (provided by electromagnet). It has linear tuning over multi-octave frequencies. Operate from few GHz to ~20 GHz. Typical output power is 15 dbm (~30 mw). - AMC (Active Multiplier Chain): The YIG signal at ~15 GHz is multiplied up by a multiplier chain based on active MMIC doubler and tripler to provide LO ~100 GHz. A Power Amplifier (PA) cascaded with coupler can be used to further amplify recombine the signals. Other types of LO sources: - Photonic: based on waveguide photomixers pumped by two lasers at ~1.55 µm. The laser beams propagate along the same optical fiber and beat in the photodiode to generate their difference frequency (used for ALMA phase reference to ~100 GHz). - QCL (Quantum Cascaded Laser): laser emission through intersubbands transitions in a repeated stack of quantum well heterostructures. Used to generate frequencies > 1 THz. - Vacuum state oscillators (klystron, backward-wave oscillator). 7/11

66 Local Oscillator system for EMIR and PdBI Band 1, 2 and 3 based on mechanically tuned Gunn oscillators 8/11 Gunn oscillator Frequency tuning Power tuning Gunn diode bias (for PLL) Gunn signal out ( GHz) LO signal out ( GHzx2) Gunn signal in ( GHz) Frequency doubler LO Band 1: GHz; LO Band 2: GHz x 2 (frequency doubler); LO Band 3: GHz x 3 (frequency tripler);

67 Local Oscillator system for EMIR and PdBI Band 4 based on electronically tuned YIG GHz YIG oscillator followed by an Active Multiplier Chain (AMC) and Power Amplifiers (PA) that delivers GHz output; - Fully electronically tuned (no more DC motors and mechanical parts fast tuning); - Cascaded tripler + filter-attenuator at ambient temperature delivers LO : GHz; 9/11

68 Looking inside the GHz Local Oscillator modules 10/11 3 db Coupler Power Amplifier Active Multiplier Chain MMIC Power Amplifier from NRAO

69 EMIR receiver noise performance across the four RF bands 11/11

70 RF band: Δ RF / RF 30-40% Typical requirements of a receiver IF band: Δ IF / RF 15% for SIS receivers, Δ IF / RF 30% for HEMT receivers LO tuning range (derives from RF and IF) and LO type (Gunn, YIG+AMC, photonic, QCL) Dual-polarization (linear or circular) with OMTs or quasi-optics wire grids. Multiband operation (observe in two RF bands simultaneously, frequency diplexing) Optimum optical coupling to the antenna Sensitivity: receiver and system noise temperatures referred to the input; cal. load Receiver technology: HEMT, SIS (DSB, SSB or 2SB) Polarization purity Stability: total power stability expressed as Allan deviation Linearity Freedom from spurious response (suppression of image sideband) Power level (in dbm/mhz) at the IF receiver output IF passband flatness (minimum slope and ripple) Full remote control of all functions (bias, temperatures, etc.) No cryogenic fluid refills: closed cycle cryocooler Screened from external RFI environment and free from self-generating RFI

71 Key specifications of ALMA (heterodyne) receivers 1/7 Band Manufacturer Frequency Mixing Scheme Noise Temperature Cryo LNA Technology 1 ASIAA GHz USB 26 K (SSB) 2 HEMT GHz LSB 47 K (SSB) 2 HEMT 3 HIA GHz 2SB 60 K (SSB) 4 SIS 4 NAOJ GHz 2SB 82 K (SSB) 4 SIS 5 Chalmers /SRON GHz 2SB 105 K (SSB) 4 SIS 6 NRAO GHz 2SB 136 K (SSB) 4 SIS 7 IRAM GHz 2SB 147 K (SSB) 4 SIS 8 NAOJ GHz 2SB 292 K (SSB) 4 SIS 9 SRON/NOVA GHz DSB 261 K (DSB) 2 SIS 10 NAOJ GHz DSB 344 K (DSB) 2 SIS For 66 receivers 1848 Two main technologies: SIS mixers and HEMT amplifiers; Noise specs few times the quantum limit T Q =hn/k B (~5 K@100 GHz); Dual linear polarization; Each receiver delivers 8 GHz of IF band per polarization channel;

72 In each antenna, one cryostat accommodates 10 receiver cartridges 2/7 Necessary for operating mm and sub-mm high sensitivity SIS mixers and cooling of other electronic components ; Close cycle cryocooler allows for long term (> 1 year) unattended operation; IR filters are mounted on the inner shields to prevent IR radiation from entering and warming up the 4K stage;

73 ALMA Band 7 receiver cartridge and specifications (developed and produced at IRAM 73 units delivered) Property Mixing scheme RF port frequency range LO port frequency range IF bandwidth SSB receiver noise Image band suppression Total IF output power integrated over 4-8GHz IF power variations across 4-8GHz Large signal gain 300K input Required Performance Linearly polarized Sideband Separating Mixer GHz GHz 4-8 GHz 2SB <147K over 80% of the RF frequency band <221K at any RF frequency <300K in GHz extended band >10dB, with allowance: no more than 10% <10dB no more than 1% <7dB Globally over all LO settings -32dBm -22dBm 5dB p-p over any 2GHz window 7dB p-p full band <5% 3/7 Amplitude stability: Allan variance 0.05s s 4.0E-7, 3.0E-6, respectively Signal path phase stability 7.1fs over 300s Aperture efficiency >80% Polarization efficiency 99.5% polarization coupling, (equiv< 23dB) Focus efficiency >98% Polarization alignment accuracy < 2 Beam squint Stabilization time from nonoperational Stabilization time from stand by mode Added cartridge mass 1/10 FWHM < 15 min < 1.5 s < 2.38kg on cold stages

74 ALMA Band 7 cartridge validation (using Cartridge Test Set) 4/7

75 Integrated noise temperature over 4-8 GHz for 65 ALMA Band 7 production cartridges 5/7

76 ALMA cold cartridges 73 for each band (including spares) 6/7 Band 5 Chalmers/ SRON Production completed Production underway Production recently started

77 First ALMA Front-End with 8 cartridges (Band 3 to Band 10) 7/7

78 1/8

79 Heterodyne Array Receivers for the IRAM 30 m telescope 2/8 HERA: 3x3 dual-pol. SIS heterodyne receiver array for 1.3 mm band In operation 230 GHz Continuum on URANUS

80 Proposed implantation of future 3 mm multibeam receiver inside the IRAM 30 m telescope cabin 3/8

81 4/8 FOV ~5.7 2 x HPBW = 48 at 100GHz

82 5/8

83 6/8

84 7/8

85 8/8