CryoPAF GHz cryogenic phased array feed receiver

Transcription

1 CryoPAF GHz cryogenic phased array feed receiver Lisa Locke 1, Dominic Garcia 1, Mark Halman 1, Doug Henke 1, Gary Hovey 2, Frank Jiang 1, Lewis Knee 1, Gordon Lacy 2, Vlad Reshtov 1, Michael Rupen 2, Bruce Veidt 2 NRC Herzberg Institute for Astrophysics (HIA) 1 Victoria, BC, Canada 2 DRAO Penticton, BC, Canada

2 Contents Introduction phased array feeds Cryogenic receiver system Cascaded noise Radome Backend electronics / digital beamformer Single antenna element Coaxial feed design Surface currents Radiation patterns Manufacturing Array Performance Beamforming with 9, 48 elem Radome effects Radiation patterns Optical coupling with reflector Conclusions 2

3 1. Introduction Microwave (1-10 GHz), millimeter wave ( GHz) has unique astronomical information. Currently single pixel receivers, but want wider field of view, without compromising sensitivity Use image plane of radio telescope to increase the area that can be imaged at once. * Multibeam receivers multiple horn feeds, receivers, & detectors -> requires multiple passes * Phased array feeds closely spaced feeds, multiple receivers, sum with complex weights in beamformer. -> single pass 3

4 2. CRYOGENIC PHASED ARRAY FEED SYSTEM DESIGN GHz (10.7 cm 5.8 cm) 48 cm diameter cryostat Composite laminate radome Multi-layered RF transparent IR shields Array (16 K physical) 31 cm diameter 140 all metal dual-linear Vivaldi elements 2.8 cm square grid spacing 3.5 K Low noise amplifier (16 K physical) Sampling and 18 beam dualpolarization freq. domain beamformer 4

5 2. CRYOGENIC PHASED ARRAY FEED SYSTEM DESIGN 2.1 Cascaded Noise single active element Noise estimate based on single active element receiver Cascaded Gain/Loss, cumulative noise temperature and physical temperature Radome: ~0.15K 5 K mutual coupling* between elements Low Noise Amplifer: 35 db at 3.5 K noise temperature Post Amp (PA): 30 db at 5 db noise figure Receiver temperature 10 K 5

6 2. CRYOGENIC PHASED ARRAY FEED SYSTEM DESIGN 2.2 Laminate Radome DRAO Penticton, BC, Canada Elliptical radome, diameter 480 mm (18.9 ), height 154 mm (6.1 ), 0.7 mm thick Composite pre-preg material: TenCate 4 quartz glass fiber (εε rr =4.5) layers infused with: Cyanate ester resin (εε rr = 3.7, tan δδ =.005) Resulting combination: Low dielectric constant (εε rr =3.32) and low dissipative loss (tan δδ =.0035 at 5 GHz) Mechanically strong, holds a vacuum Low moisture absorption, low outgassing Used in other radome & space/satellite applications Vacuum infusion: glue infused quartz weave air + heat + time = radome Create mold, fabricate on site 6

7 Vacuum Infusion Lab - Penticton 7

8 2. CRYOGENIC PHASED ARRAY FEED SYSTEM DESIGN 2.3 Backend Electronics / Digital Beamformer Digitization Inputs from 96 active antenna elements, 10 Gsps, 4-bit U of Calgary: Xu, Y., Belostotski, L. and Haslett, J.W., "A 65-nm CMOS 10-GS/s 4-bit backgroundcalibrated noninterleaved flash ADC for radio astronomy," IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 22, (2014). put on fibre Frequency band selection 6 DRAO Kermode boards with FPGAs selects and bandlimits signal with programmable bandwidth Channelized to 1 MHz with polyphase filter bank Freq Domain Beamforming & array covariance matrix calib. FPGAs compute 18 polarized beams (36 beams total) In single dish mode the beamformer FPGAs compute the integrated auto-power spectrum for the PAF 8

9 3 SINGLE ANTENNA ELEMENT Vivaldi element simulated with full-wave solver CST Microwave Studio 2016 Vivaldis : large bandwidths narrow physical width (λ/2 at high freq) (dense array) can be made all-metal for cryogenic cooling Symmetric radiation patterns in E- & H-planes Low side lobes Good cross-polarization properties 9

10 3 SINGLE ANTENNA ELEMENT 3.1 Coaxial Feed Design Antenna: electric field in slot line need to pick up to transmission line Discrete Probe: ideal: first approx Coaxial Feed: realistic 2-section coax Validated: 50 ohm impedance, input reflection coefficient, S11 low, single mode TEM propagation 10

11 3 SINGLE ANTENNA ELEMENT 3.3 Radiation Patterns Far field normalized gain for L to R: 2.8, 4.0, 5.18 GHz Spherical coordinates: φ cut planes E (φ = 90 ), D (φ = 45 ) H (φ = 0 ) vs elevation angle, θ Co-pol and cross-pol, Ludwig 3 rd. -> Expected results: very broad, ~ constant with frequency φ θ 12

12 3 SINGLE ANTENNA ELEMENT 3.4 Manufacturing - 3 Piece Dart 2D electric model -> 3D manuf model Better suited for small antenna elements (28.8mm) than previous 2D manuf methods 13

13 3 SINGLE ANTENNA ELEMENT 3.4 Manufacturing Copper Elements - 3 Piece Dart 14

14 3 SINGLE ANTENNA ELEMENT 3.4 Manufacturing - 3 Piece Dart 15

15 WITH RADOME WITHOUT RADOME 4.0 ARRAY PERFORMANCE S_active: Simultaneous Excitation Active Input Reflection Coefficient Horizontal elements, one quadrant Effect of 0.7 mm radome, modeled as a homogeneous dielectric, εε rr = 3.32, tan δδ =.0035 Even complex excitation: 1, 0 Active Input reflection (db) measurements: Sn => Sn_active 16

16 4.0 ARRAY PERFORMANCE 4.4 Radiation Patterns Active radiation patterns for 2.8 GHz / 4.0 GHz / 5.18 GHz All 48 horizontal elements stimulated, with amplitude = 1, phase = 0 Directivity patterns vs elevation angle θ ( ) Co-pol H-, E-, D-planes (φ = 0, 90, 45 ), cross-pol D-plane No radome (left), With radome (right) Results: Radome barely affects beam patterns HPBW reduces with frequency as expected. φ θ 17

17 9H formed beam is close to 0.75 total efficiency Need to optimize # of elements included to increase total efficiency Upper limit on beam size: all 48 elem gives narrowest beam. 18

18 0.7mm radome, 48 element formed beam, 3.99 GHz, E-field 19

19 Theoretical RF Loss & Reflection Radome Optical view of dielectric behaviour 2 interface (vacuum / dielectric / vacuum) problem with single dielectric slab of finite width ll 1. Calculate RF loss and input reflection. Incorporate reflections from both interfaces Assumptions: normal incidence of wave single polarization surrounded by vacuum (n a =n b =1) Permeability μμ rr = 0 for reflection: assume lossless slab (i.e. ee rr = 0) ee rr ee rr ee rr tanδδ DD QQ nn dielectric constant, complex permittivity, real permittivity, imaginary loss tangent, real dissipation factor, real quality factor index of refraction Definitions: ee rr = ee rr jjee rr tanδδ = ee rr ee rr = DD = 1 QQ Loss tangent vector diagram. Image from Agilent App note Agilent Basics of Measuring the dielectric properties of materials. nn 1 = 1 ee rr +μμ rr Reflected and Transmitted signals. Image from Agilent App note Agilent Basics of Measuring the dielectric properties of materials. 20

20 Theoretical RF Loss & Reflection Radome Inputs: λλ, ee rr,tanδδ, ll 1 (thickness). From Orfanidis, Electromagnetic Waves and Antennas, Section 5.4 Single dielectric slab 1. Calculate wave impedance, ZZ 1, then reflection coefficient, Γ 1 (Snell s Law at front (a to 1) interface) Γ 1 = nn 1 nn aa nn 1 +nn aa = nn 1 1 nn Calculate loss due to attenuation: αα dd = ππ ee rr tanδδ [Np/m] x [db/np] x ll λλ 1 [m] 21

21 Theoretical RF Loss & Reflection 0.7 mm Radome, physical temp 290 K, ee rr = 3.32, tanδδ = Loss (K) Input Reflection (db) 2.8 GHz 0.08 K db 5.18 GHz 0.15 K db 22

22 4 ARRAY PERFORMANCE 4.5 Optical Coupling with Reflector Offset Gregorian optics of DVA-1 telescope at DRAO Penticton, with white ray-traces from to computed with GRASP (PO, PTD, GO). Primary reflector: D=15 m projected diam Half-opening angle: 55 Feed edge taper: -16 db The antenna array will be placed at the of the subreflector. When coupled with reflector: λ/d in the λf/d in the where f: focal length 23

23 4 ARRAY PERFORMANCE 4.6 Focal Plane Beams Overlaid on antenna elements in focal plane: 3dB width of beam: FWHM (3 db circles) Spacing of beams: Nyquist spacing λ/2, Δ Signal processing power of beamformer-limited FWHM Δ 2.8 GHz 36 beams fills array. But only have 18 dual-pol available GHz Could use many more beams 120 mm 230 mm 24

24 4 ARRAY PERFORMANCE 4.7 Far-field Beams FWHM Δ 1 1 Using D=15m offset Gregorian reflector, farfield beam simulation Single beam 18 beams 36 beams 2.8 GHz 5.18 GHz 0.41 x 0.41 = 0.17( ) x 0.22 = 0.048( ) x 0.8 = 1.28 ( ) 2 (7.5x) 1.6 x 1.6 = 2.56 ( ) 2 (15x) 1.0 x 0.4 = 0.4 ( ) 2 (8.3x) 1.0 x 0.8 = 0.8 ( ) 2 (16.6x) 25

25 5 CONCLUSIONS Cryogenic (16 K) PAF for GHz designed Trx = 10 K Composite laminate radome 140 metal Vivaldi antenna elements 96 low noise (T = 3.5 K) amplifiers Post amplification, filtering FD Digital beamformer 18 beams for now Can attain ~8x FoV of SPF for 18 beams and ~16x FoV for 36 beams assuming overlap well within 3 db Airy circles. 4-element antenna prototype: Spring 2017 Future: 4-element antenna + coax + LNA: and thermal testing dewar construction Test 4-element prototype in dewar Full array construction 26

26 Thank you NRC Herzberg Astronomy and Astrophysics Lisa Locke Engineer 27

27 3 SINGLE ANTENNA ELEMENT 3.4 Manufacturing - 2 Piece Arabesque 28

28 3 SINGLE ANTENNA ELEMENT 3.4 Manufacturing 3D printing - 2 Piece Arabesque 29