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PHAROS2 Phased Array Feed: Warm Section,

signal transportation and iTPM digital backend

A. Navarrini1, J. Monari2, A. Melis1, R. Concu1, A. Scalambra2, A. Maccaferri2, A. Cattani2, P. Ortu1,

G. Naldi2, J. Roda2, F. Perini2, G. Comoretto3, M. Morsiani2, A. Ladu1, S. Rusticelli2, A. Mattana2,

G. Bianchi2, L. Marongiu1, M. Schiaffino2, E. Carretti1, A. Saba1, F. Schillirò4, E. Urru1, G. Pupillo2,

M. Poloni1, T. Pisanu1, R. Nesti3, G. Muntoni1, K. Zarb Adami5,6, A. Magro5, R. Chiello6

1 INAF-Osservatorio Astronomico di Cagliari, Selargius, Italy 2 INAF-Istituto di Radioastronomia, Bologna, Italy

3 INAF-Osservatorio Astrofisico di Arcetri, Florence, Italy 4 INAF-Osservatorio Astrofisico di Catania, Catania, Italy

5 University of Malta, Malta 6 University of Oxford, Department of Physics, UK

PAF2017 Workshop, Sydney, Nov. 16th 2017

PHAROS System Overview

• International collaboration, FARADAY FP5 Radionet programme,

started over 10 years ago;

• Cryogenically cooled PAF with analog beamformer designed to

produce 4 synthesized beams;

• Each beam is synthesized with 13 focal plane antenna elements:


PHAROS System Overview

• International collaboration, FARADAY FP5 Radionet programme,

started over 10 years ago;

• Cryogenically cooled PAF with analog beamformer designed to

produce 4 synthesized beams;

• Each beam is synthesized with 13 focal plane antenna elements:

1

1

1

1

1

1

1

1

1

1

1

1

3 3

3 3

3

3

3

3

4

4

4

4

• Array of 10x11 dual-pol. Vivaldi antennas;

• Total n. of radiating elements 24 (+dummies)

in one polarization;

• Vivaldi antenna pitch is 21 mm;

• C-Band (4-8 GHz) with focus on 5-7 GHz;


PHAROS


PHAROS2 main specs

• Re-use some of existing PHAROS hardware;

• New cryogenic LNAs with state-of-the-art performance (from

LNF) to replace the existing ones;

• Design and possible fabrication of new radome (UMAN, Chalmers

and in-kind contribution from NRC);

• Digital backend (at room temperature) to replace existing analog

beamformer (INAF, Univ. Malta);

• Pre-filtering, amplification and downconversion: Warm Section

(INAF);

• IF over Fiber (IFoF) analog signal transportation (INAF);

PHAROS2 framework and partners


• SKA Advanced Instrumentation Program on PAF;

• C-band PAF demonstrator with digital beamformer;

• Partners: INAF, UMAN, ASTRON, Chalmers Univ., Malta Univ.;

• Fast C-band continuum surveys, and polarization meas. in particular in the

Galactic Plane (to improve existing surveys to 2.5’ resolution);

(Non comprehensive) science possibilities at

C-band with cryo PAF

• High Dispersion Measure pulsar searches toward the Galactic Centre and inner

Galaxy;

• Excited rotational states of OH near 6.03 GHz: Zeeman effect, star formation;

• CH3OH (6.7 GHz): survey of methanol masers, gas kinematics, UC HII region;

• Formaldehyde line emission at 4.8 GHz;

• Flat spectra transients/pulsars, like magnetars;

• Hydrogen recombination lines around 5 GHz;

• CMB foregrounds;

• Gamma Ray Burst and Gravitational Wave event follow-ups;

• FRB search;

• Confusion limited polariz. mapping of Galaxy Clusters and Supernova Remnants;


PHAROS2 more detailed specs RF range: 4.0-8.0 GHz

Frequency downconversion type: Single, with sideband separation mixer (2SB), LSB

LO frequency range: 4.650-8.375 GHz (LSB tuning)

IF frequency range: 375-650 MHz (275 MHz instantaneous bandwidth)

N. of active antenna elements: 24 (out of 220 Vivaldi antenna elements)

N. of compound beams: 4 (using 24 antenna elements)

N. of polarizations: 1 (single-polarization)

Selectable RF filters, frequency

ranges and LO tuning

frequencies:

Selection of one BPF out of four possible ones:

a) 4.0-8.0 GHz; LO tunable anywhere across 4.65-8375 GHz

b) 4.775-5.050 GHz (Formaldhyde at 4.8 GHz and H recombination

lines); LO fixed at 5425 MHz;

c) 5.78-6.055 GHz (Excited rotational states of OH near 6.003 GHz);

LO fixed at 6.43 GHz;

d) 6.445-6.720 GHz (Methanol maser line at 6.668 GHz); LO fixed at

7.095 GHz;

When options b), c) or d) are chosen the mixer image sideband rejection

is increased by the filter rejection (total expected> 40 dB);

IF signal transportation: Two IF signals transported over a single optical fiber (IFoF) using

Wavelength Division Multiplexing (1270 nm and 1330 nm)

Backend and beamforming: Digital backend with one iTPM (Italian Tile Processing Module)

capable of digitizing 32 inputs, 512 frequency channels

RFI situation at C-Band at JBO and PHAROS2 BPFs


fLO(b)=5425 fLO(c)=6430

fLO(d)=7095

Schematic diagram of PHAROS2

Design of PHAROS2 Warm Section (WS)

Standard 6U rack (19”) with: 4 WS RF/IF modules, 1 LO distribution module and 3 power

supplies: handling 32 x RF input signals, 24 from cryostat + 1 calibration from noise source

(7 unused);

LO

distribution

module

3 × Power

supplies 4 WS RF/IF modules

Fiber-Ethernet

media converter

Power switch

and plug

PCB: view of layers and RF/LO/IF components: WS module:

4 laser TXs

8 x RF inputs

1 LO input

4 optical fiber outputs

PCB integrated

in mechanical

module

• One WS module has 8 x RF inputs, 1 LO input and 4 WDM IFoF outputs (4 laser OTXs);

• Single four-layer PCB with surface mount components (no bonding, easy assembly,

low-cost) inside mechanical housing. Biased with a single 5 V voltage;

• 1 LO input internally distributed with 8-way splitter (+filtering section and LO ampl.);

RF1

RF2

RF3

RF4

RF5

RF6

RF7

RF8

LO

IF1

IF2 IF3

IF4

IF5

IF6

IF7

IF8

RF5

RF2

RF3

RF1

RF4

RF6

RF7

RF8

LO


Design of WS RF/IF module:

To 4 laser

OTXs

LO in = 0dBm

LO distribution chain

RF chain with BPFs, including amplifier and

mixer conversion loss

IF chain: from mixer output to optical

transmitter input

RF chain with BPFs, including amplifier and

mixer conversion loss

Electromagnetic simulation results of WS module G

ain (

dB

) G

ain (

dB

)

Gai

n (

dB

)

Gai

n (

dB

)

IF over Fiber (IFoF)

CWDM (Coarse Wavelength Division Multiplexing) for IF over fiber

technology. Developed for SKA LFAA by INAF-led collaboration:

- Two different IF signals (from two different single-pol antenna elements)

transmitted over same optical fiber using different optical carriers

at =1270 nm and =1330 nm;

- Dual laser sources and dual photodiode detectors in single packages.

- Isolation between channels: >45 dB (375-650 MHz);

- Demultiplexed at optical receiver side;

- Half FO, connectors, fusion splices, fibre joints (compared to more

standard non-multiplexed links);

- Widely used in fiber optic communication systems low cost;


IFoF Links (AAVS1-SKAlow): Optical Transmitters (OTXs)

LC/APC

optical

pigtail

Two MCX

connectors

EMI filter

feed through

IFoF Links (AAVS1-SKAlow): Fiber Optic Receivers (ORXs)

IF coax

output 1

IF coax

output 2

Fibre

Optics

Input

Two independent IF chains (red and blue). Each channel adapts the signal for the digital

conversion by ADU: amplification, level adjustment with digital step attenuator (31 dB range,

1dB step), band selection with a filter bank (low band, 50–375MHz, or high band, 375–

650MHz) and a switch to close the IF input of any receiver on a 50 Ohm load for debugging

procedures. Receiver control with SPI bus from ADU board.

Optical receiver (located inside preADU):


2+1 spare preADUs,

each with 8 ORXs

Example of qualification report of one

IFoF link (AAVS1-SKAlow ORX)


PHAROS2 digital backend based on iTPM

ORXs

preADU#1

preADU#2 ADU

Optical Pigtail (from

back to Front Panel)

One iTPM includes one ADU (Analog Digital Unit) and two preADUs:


16

LC/APC

Optical

Inputs

ADU heatsink

QSFP+ for

40GbE network

PPS

input 10MHz

Input

1Gb Ethernet

Front Panel

Size: 6U and

21HP

Assembly

Depth: 465mm


PHAROS2 digital backend based on iTPM

• Accepts 32 analog inputs, 500 MHz BW;

• 16 dual-ADCs AD9680, JESD204B, 1 GS/s ENOB=10.8;

• 2 x FPGAs XILINX Ultrascale XCU40 20 nm;

• 2 x DDR3 96 bit memory banks, 6+6 Gbit total size;

• Digitisation at 700MS/s 375-650 MHz sampled in

second Nyquist zone; (in PHAROS2 the signals are

reversed twice - LSB tuning plus second Nyquist -

resulting in non-reversed passbands);

• 2 x 40Gbps Ethernet interfaces (QSFP), one for each

FPGA;

• High speed internal bus to connect the 2 FPGAs,

25 Gbps + 25 Gbps bidirectional;

ADU (Analog Digital Unit) overview


Development of digital backend for PHAROS2 • 25 IF inputs (24+1 cal) across 375-650 MHz from IFoF to iTPM;

• iTPM initially used for digitization and channelization with oversampled PFB:

512 sub-bands (≈0.68 MHz/ch) in complex representation through FFT;

Three milestones for beamforming implementation: Milestone 1: implementation of beamforming of one single iTPM channel, 0.68 MHz BW

(350MHz/512) on CPU with the Medicina software pipeline developed for a space debris

project. Use 24 elements single polarization to form 4 beams.

Milestone 2: Implementation of 4 beams for 24 iTPM frequency channels from 24 single

polarization antenna elements, for a total of 16 MHz BW, using CPU.

Tests performed on the BEST-2 array It required to modify the firmware.

Milestone 3: Implementation of beamforming in the iTPM FPGAs for 24 elements, single

polarization, 4 beams with ≈250 MHz BW.


The “Northern Cross” Medicina

Radio Telescope

E/W arm

Single antenna

564 m x 35 m

N/S arm

Array of 64 antennas

640 m x 23.5 m

E/W arm

N/S arm

Total area = 28000 m2

N. of dipoles on the focal lines = 5632

Frequency = 16 MHz @ 408 MHz

2000 Km of steel wires

as reflecting surface.


BEST-2 Array (SKA Demonstrator) • BEST-2 used for development and testing of Milestone 2;

• 32 receivers installed in 8 cylinders of the North-South arm of the

Northern Cross radiotelescope (4 rx per cyl.);

• Collecting area = 1400 m2 (equivalent to a parabolic dish of 42 m);

• Single polarization;

• RF bandwidth: 400-416 MHz. IF bandwidth: 22-38 MHz;

• Optical fiber links from the antennas to the receiver room;

Digital backend for PHAROS2 : Milestone2

1

ADCs 800 MSPS

Polyphase Filter Bank

512 points 781.25 KHz

Res.

2

3

24

Amplitude and Phase Calibration

Quantization

Channel Selection

20 freq. channels

10 GbE Tranceiver

FPGA

10 GbE Tranceiver

Correlator 276 cross-corr.

Calibration

Amplitude and

phase coefficients

Multi-beamformer 5 beams

Integration Time ~1sec.

CPU

Implementation of 4+ beams for 24 iTPM frequency channels from 24 single

polarization antenna elements, for a total of 16 MHz BW, using CPU


ADU

Channel Selection

24 freq. channels

Four beams, each beam provided with integrated spectra (pulsar search, on-the-fly mapping) and with non integrated spectra (pulsar timing).


Digital signal processing in iTPM: Milestone 3

Implementation of beamforming in the iTPM FPGAs for 24 elements,

single polarization, 4 beams with ≈250 MHz BW.

PHAROS2 Backend Cabinet

Intellinet I-CASE EPX-4210BKX:

Standard 19" racks, height 42U;

External dimensions: 800x1000x2057 mm3;

Power supply (2U)

Power distributor (1U)

Subrack with 1 iTPM (6U)

Air deflector (3U)

Switch 1G (1U)

Switch 40G (1U) required for future upgrade

Server (4U)


To do:


• Developed an architecture of PHAROS2 with digital backend;

• Designed a WS rack (with 4WS RF/IF modules, 1 LO splitter, etc);

• Developed a prototype of Warm Section RF/IF module

and of LO splitter;

• Procured IFoF OTXs and ORXs (preADU: 2+1 spare);

• Procured 2 ADUs (1+1 spare);

• Put together one iTPM (2 preADU and 1 ADU);

• Achieved Milestone 1 and Milestone 2 of digital backend

development with iTPM for PHAROS2;

Conclusions

• Start production of WS RF/IF modules (4 required);

• Complete purchase of mechanical and control electronics parts for WS;

• Complete Milestone 3 of digital backend development;

• Ship hardware to Jodrell Bank and install it on the 76-m Lovell telescope;

• Run a scientific project;

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