Design and Development of a Wide-Field Fully Cryogenic ...

Cornell'University.Ithaca&NY&14853,&USA&

Design and Development of a Wide-Field Fully Cryogenic Phased Array Feed for Arecibo

Mitchell C. Burnett, Jakob Kunzler, Erich Nygaard, Brian D. Jeffs, Karl F. WarnickDepartment of Electrical and Computer Engineering

Brigham Young University, Provo UT, USA

Donald Campbell, German Cortes-Medellin, Stephen Parshley, Amit VishwasCornell Center for Astrophysics and Planetary Science

Cornell University, Ithaca, NY, USA

Phil Perillat and D. Anish Roshi

Arecibo Observatory, Arecibo Puerto Rico, USA


ALPACA Grant Details• NSF Award AST-1636645• Brigham Young University, Cornell

University, UCF• 4 years, $5.8M• Cornell: PAF front-end, including

electronics, array elements, dewar, cryogenics, mechanical engineering• BYU: Overall project management,

signal downlink, digital beamformer, data handling• UCF: Site preparation, installation and

testing support.• 2.5 year funding wait over!


The PAF Narrowband Digital Beamformer

§ Repeat for each frequency channel.

§ wk is frequency dependent.

§ wk steers beam mainlobe towards(i)

+

w*1

w*3

w*M

b(i) = w y(i) H

θ

Space signalof interest

Noise :

Interference

y (i)1

y (i)3

y (i)M

n (i)1

n (i)M

s(i)

z (i)1 ��

bk (i) =wkHyk (i)


• Densely-packed simultaneous beams• Fully sample the optics-imposed

field of view• Potential for adaptive spatial

filtering to null RFI sources• Potential for beampattern shape

control to combat comay(i)

s(i)z(i)

Radio telescope dish with a phased array feed

Beamforming Capabilities


Field of view comparedto existing 7 beam ALFA receiver:

PAFS are all about survey speed and sky mapping


Performance compared to other astronomical receivers


Science Goals for ALPACA

• ALPACA design is targeted for: • HI and other long-integration, fine resolution spectral line observations• Pulsar/transient observation and parameter estimation

• Primarily a survey and mapping instrument due to wide field of view


ALPACA System Architecture

! ! ! ! ! ! ! ! !

2

3 4

1

LNA

T=80KTA

Cryostat

T=15K

Signal Conditioning

λx138

RF/O

RF/O

FO Link

Signal Conditioning

ALPACA Cryo PAFArchitecture Rev Jun, 2019

x138

Digital Beamformerx138

G= 35 dB

Te = 5K x138

IL=Flo: Fhi:

BPF

NF=3dBGmin=Gmax=

VGA

138

Test4

ADC

! ! ! ! ! ! ! ! !

2

3 4

1

Test2Test1

!!!!!!!!!

3

2 1

4

Test3

!!!!!!!!!

3

2 1

4

X"engine'F"engine'

1

Equations

German Cortes M., Nov 21, 2011, (Rev. August 7, 2015)

I. NON LINEAR FIT: FIELD INTENSITY AT APERTURE PLANE

Best fit of the near fields peak intensity at a radial distance r in wavelengths,

|Epeak(r�)| = bo + b1 ln (r� � ro) [dB] (1)

bo = �2.50745 (2)

b1 = �3.55645 (3)

ro = �1.9473 (4)

xi = !j (5)

yj =X

i

!ji xi (6)

REFERENCES

[Kathuria, 1983] Y. P. Kathuria, “ Far-Field Radiation Patterns of Elliptical Apertures and its Annulli ”, IEEETransactions on Antennas and Propagation, Vol AP-31, No. 2, March 1983, pp. 360-364.

1

Equations

German Cortes M., Nov 21, 2011, (Rev. August 7, 2015)

I. NON LINEAR FIT: FIELD INTENSITY AT APERTURE PLANE

Best fit of the near fields peak intensity at a radial distance r in wavelengths,

|Epeak(r�)| = bo + b1 ln (r� � ro) [dB] (1)

bo = �2.50745 (2)

b1 = �3.55645 (3)

ro = �1.9473 (4)

xi = !j (5)

yj =X

i

!ji xi (6)

REFERENCES

[Kathuria, 1983] Y. P. Kathuria, “ Far-Field Radiation Patterns of Elliptical Apertures and its Annulli ”, IEEETransactions on Antennas and Propagation, Vol AP-31, No. 2, March 1983, pp. 360-364.

Ae

Tsys=

kB B

S

wHRsw

wHRnw

m2

K

�(9)

Ae

Tsys=

kB B

S

hw|Rs|wihw|Rn|wi

(10)

Ae

Tsys=

kB B

S

hW |Rs|W ihW |Rn|W i

(11)

Y (!) = hw(!)|x(!)i (12)

Y (!) =wH(!)x(!) (13)

yj =X

i

!ji ⇥ xi (14)

Y (!) = hw(!)|x(!)i (15)

Rs(!) = EnxxH

o��n=0

(16)

Rs(!) = Enx(!)x⇤(!)

o��n=0

(17)

SY (!) = EnY (!)Y ⇤(!)

o(18)

SY (!) = hW (!)|Rs(!)|W (!)i (19)

SY (!) = wH(!)Rs(!)w(!) (20)

SN(!) = wH(!)Rn(!)w(!) (21)

SNR =wHRsw

wHRnw(22)

2

Array Beam FromingCreated by G. Cortes, Jan 12, 2014

Last Rev. August 25, 2015

1 Max SNR

|x(t)i = |ais(t) + |ni(t) (1)

x(t) =

2

6664

x1(t)x2(t)...

xM(t)

3

7775(2)

|x(!)i = |ais(!) + |ni(!) (3)

|x(!)i =

2

6664

x1(!)x2(!)

...xM(!)

3

7775(4)

x(!) = a⌦ s(!) + n(!) (5)

x(!) =

2

6664

x1(!)x2(!)

...xM(!)

3

7775(6)

Rn = En|nihn|

o(7)

Rn = EnnnH

o��s=0

(8)

Rn = Rspl +Rsky +Rloss +Rrec

1

Front-End

NF=Gmin=Gmax=

VGA2x69

69 Dipoles

-3 dB, Te=290KF1=1300 MHzF2=1720MHzBW: 420 MHz

BPF


ALPACA Performance Specs. (1)Performance Characteristic Specification

Frequency Coverage (tunable within this range) 1300 – 1720 MHz (420 MHz total BW)

Beamformer real-time processing bandwidth 305.2 MHz

Number of real-time beams 40

Integrated spectra data products per beam, per channel XX pol (real float), YY pol (real float), XY pol (complex)

Pulsar / Transient mode:

Number of frequency channels | BW per channel 1250 coarse chan. | 244.1 kHz separation, 325.5 kHz BW

Fastest integration dump interval 64 microseconds

HI Spectral Line (zoom spectrometer) mode:

Total number of frequency channels | BW per channel 36,000 (spanning 183.7 MHz) | 5.1 kHz

Shortest integration dump interval 100 ms

Beamformer calibration mode:

Covariance matrix outputs per each 512 coarse channel Lower triangular 144x144 matrices, 500 ms max dump rate



LO and IF frequencies NONE: direct sampling of bandpass RF

ADC sample rate | resolution 2,000 Msamp/s | 12 bits (10+ enobs)

Complex baseband sample rate 500 Msamp/s

1st stage PFB FFT length | oversample ratio 2048 channels | 4/3 oversampled

2nd stage (zoom) PFB length | oversample ratio 64, pruned to 48 non-overlapped channels | 1/1

Peak I/O data rates:

Output data rate per FPGA board | input rate per HPC 52.1 Gbps | 37.5 Gbps (8 bit real + 8 bit imag. samples)

Total max output data rate in pulsar spectrometer mode 50.0 Gbps (16 bit int real & 32 bit int complex: 16r+16i)

Optional (unfunded) beamformed voltage data mode: (Ability to support these modes is undetermined)

Beamformed raw voltages data rate, total over all HPCs 520.8 Gbps (cmplx int 16, 40 beams, X&Y pol)

Beamformed raw voltages data rate, one HPC 20.83 Gbps (cmplx int 16, 40 beams, X&Y pol)



Number of input ports (antennas) 138 + 6 spare = 144, index: 0 £ j £ 143

Number of Xilinx ZCU216 FPGA boards | fid index 9 | index: 0 £ p £ 8, fid = p

Number of HPCs 25 index: 0 £ i £ 24

Number of GPUs per HPC 2 index: 0 £ l £ 1

Number of processing threads per GPU 1

xid index: identifies a unique GPU & hashpipe thread xid = q = 2i + l, 0 £ q £ 49

Frequency channels processed by qth xid kÎ{q, q + 50, q + 100,… q + 1200} for xid range of 0 £ q£ 49. This implies the channel index range is 0 £ k £ 1249.

Reduced bandwidth modes: total BW processed options 305.2, 244.2, 183.1, 122.1, or 61.0 MHz total BW (i.e., select and process any of 5, 61 MHz wide subbands)


• Reduced component count• Reduced processing

requirements• Similar FOV sensitivity flatness• Improved !"#" due to lower

mutual coupling and better impedance match• Reduced cryogenic cooling

complexity: 1 compressor, 3 cold heads vs 2 and 4 respectively

Array Geometry


Model steps:• Embedded element patterns

(FEM, CST)• Propagate to primary reflector• Propagate to secondary • Propagate to tertiary• Propagate to far field• Use reciprocity to determine

received voltages at the element terminals for a plane wave incident on the primary reflector

Focal pointPrimary reflectorSecondary reflector

Simulation Model


Cryo-cooler(1 of 3)

Solid top half

Antenna module (69x) 2nd stage (20 K)

1st stage (80 K)

RF clear window

Cryostat Design


LNA + Dipole Module

Initial prototype design Final Design with Optimized Dipole Element


Signal Transport: RF over Fiber

Single channel transmitter prototype design

Design rendering for the 8-channel transmitter boxthat is mounted on the outside of the cryostat


To mass storageLustre File Storeand/or other back ends

(×10)

•••

4

4

•••

XilinxUltrascale+

RFSoCFPGA

(×9)

F Engine:Sampling, Polyphase filter bank and 100 Gbe I/O

4 x 25 GbE

SFP28

XB Engine:Correlator, Beamformer, Spectrometer

•••

(× 25)

From R

F over fiber downlink receivers

GPU server2U HPC (#1)

ZCU216 board (#1)

GPU server2U HPC (#25)

Ethernet Switch

64 port100 G

bE

RTX 2080 TI GPU

RTX 2080 TI GPU

RTX 2080 TI GPU

RTX 2080 TI GPU

16 on-chip2.5 G

spsAD

Cs

4 x 25 GbE

SFP28

ZCU216 board (#9)

16 on-chip2.5 G

spsAD

Cs

XilinxUltrascale+

RFSoCFPGA

(×9)

•••

(× 25)

•••

Beamformer Subsystems


• XZCU49DR RFSoC has 16 on-chip ADCs, 2.5 Gsamp/sec, with digital down conversion and lowpass filtering to complex baseband • Will directly sample RF over fiber downlinks with no

analog mixer• 4 x 25 GbE ports support I/O data rate to HPC/GPUs.• 9 of these ZCU216 boards will be used to support 138

antenna inputs• Oversampled polyphase filter bank for coarse frequency

channelization

RFSoC F-Engine


• Passband corners: 1300 MHz to 1720 MHz

• Band-defining filter attenuates adjacent RFI prior to the RF over fiber link to limit dynamic range

• Anti alias filter is just ahead of ADC to reduce noise aliased into passband

• Pre-ADC filter is lower order, lower cost

0 500 1000 1500 2000 2500 3000 3500Frequency, MHz

-60

-50

-40

-30

-20

-10

0

Mag

nitu

de fi

lter r

espo

nse,

dB

Analog Filter Responses

Pre-RFoF filterAliased pre-RFoFPre-ADC filterAliased pre-ADC Sample frequency: fs

ADC, Sampling, and Pre-Filtering


• Built-in ADC Digital Down Converter (DDC)

• 2 GHz sample frequency• Mixes sampled real RF down

to complex baseband• Decimates to final sample

rate of 500 MHz

ADC, Digital Down Conversion


• Built-in ADC pre-decimation anti-alias filter response.

• Decimation by 4 moves. 250 MHz to full bandwidth point at 1.0.

• Complex baseband sample rate is 500 MHz.

• 420 MHz usable passband. • No NCO tuning to select 305

MHz beamformer band: just pick from PFB channels.

• Ready for upgrade to 420 MHz beamformer with more HPCs.1000 MHz

Full bandwidth point for 2 Gsps sampling

210 MHz 250 MHz

Observed band center: 1510 MHz ←→ NCO frequency

ADC, Digital Down Conversion


Selected Coarse Channels

!b!k, j[n]xk[n] bk, j[n]

100

GbE

Sw

itch

Nvidia RTX 2080 Ti GPU, 1 of 2 per HPC

OversampledPFB channelizedpackets

Lustr

eDisk

Arra

y St

orag

e

FITS

For

mat

ter

4 X 25 GbE


Cha

nnel

Sel

ectio

n (k

= ..

. )

Select up to half of thecoarse channels, in 44 MHz blocks

Single hashpipe instance per GPU

Fine PFB

Polyphasefilter bank

(128 point FFT)

Sk,( j, j )f

Fine Spectrometer Long-term Integrator

!S !k,( j, j )f =

1N

!b!k, j[n] !b!k, j* [n]

n=0

N−1

∑

!b!k, j[n]

Real-timeBeamformer

bk, j[n]=

wk, jH x k[n]

xk[n] bk, j[n]

100 ms min. integration dump time

Channel bonded25 GbE port pair

HI Mode, Fine PFB (1 of 25 HPCs)




100

GbE

Sw

itch

Lustr

eD

isk A

rray

Stor

age

FITS

For

mat

ter

4 X 25 GbE

Real-timeBeamformer

bk, j[n]=

wk, jH x k[n]

xk[n]

Coarse Spectrometer Fast-dump Integrator

Sk,( j, j )c =

1N

bk, j[n]bk, j* [n]

n=0

N−1

∑

Sk,( j, j )cbk, j[n]

0.064 ms min. integration dump time



Cha

nnel

Sel

ectio

n (k

= ..

. )

Select up to all of thecoarse channels, in 44 MHz blocks


OversampledPFB channelizedpackets Channel bonded

25 GbE port pair

Transient Mode, Coarse PFB (1 of 25)




100

GbE

Sw

itch

Lustr

eD

isk A

rray

Stor

age

FITS

For

mat

ter

4 X 25 GbE

xk[n]

Correlator / Integrator

Rk =1N

xk[n] xkH [n]

n=0

N−1

∑Rk

Rk

500 ms min. integration dump time



Cha

nnel

Sel

ectio

n (k

= ..

. )

Select up to all of thecoarse channels, in 44 MHz blocks

OversampledPFB channelizedpackets Channel bonded

25 GbE port pair


Beamformer Calibration Mode (1 of 25)

Design and Development of a Wide-Field Fully Cryogenic ...

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