Karl F. Warnick, David Carter, Taylor Webb, Brian D. JeffsDepartment of Electrical and Computer EngineeringBrigham Young University, Provo, UTwarnick@byu.edu

J. Richard Fisher and Roger NorrodNational Radio Astronomy ObservatoryGreen Bank, West Virginia

April 2010

Active Impedance Matched Dual-Polarization Phased Array Feed for the GBT

BYURadio Astronomy Systems

Research GroupCollaborations

Marianna Ivashina, Rob Maaskant, and Stefan Wijnholdshave been working hard at BYU on polarimetric calibration

BYURadio Astronomy Systems

Research GroupPAF Development Efforts

19 element very low loss active impedance matched array– Fabricated, sky noise measurements completed (Nov. 2009)

19 x 2 element dual-polarized array– Element design and fabrication– Room temperature 33 K LNAs– Four channel downconverter boards– 40 channel real time data acquisition system

Cryogenic PAF – dewar and LNAs (R. Norrod, NRAO) Signal processing algorithms

– Beamformers with high sensitivity and controlled beam shape– RFI mitigation algorithms for PAFs– Polarimetric calibration and beamforming

PAF model performance simulations for PrepSKA Arecibo PAF feasibility study (G. Cortes) CASPER ROACH FBX engine (J. Landon @ Berkeley)

BYURadio Astronomy Systems

Research GroupSystem Noise Budgets

Component 2008(Measured)

2009(Target)

Cryogenic PAF(GBT)

Sky 4 4 4

Spillover 5 5 5

Antenna Loss 4 1 5

LNA Tmin 33 33 5

Mutual Coupling 20 3 1

Total 66 K 46 K 20 K

BYURadio Astronomy Systems

Research GroupActive Impedance Matched Array

Design goals:– Extremely low loss– Ground plane backed– Integrated balun– 300 MHz bandwidth (1 dB sensitivity)– Active impedance matched to formed PAF beams over FoV

BYURadio Astronomy Systems

Research GroupDesign Optimization Process

Computationally challenging! Dave Carter, Taylor Webb (MS students)

Single Element

7 x 2 Element

Array

19 x 2 Element

Array

HFSSSensitivity Cost

Function(Reflector Model)

Infinite Array

Unit Cell

BYURadio Astronomy Systems

Research GroupSingle-Pol Prototype

BYURadio Astronomy Systems

Research GroupPassive and Active Return Loss

BYURadio Astronomy Systems

Research GroupNoise Temperature and Sensitivity FoM

~500 MHz 1 dB Sensitivity Bandwidth

BYURadio Astronomy Systems

Research GroupMeasured Single-Channel Noise Performance

Modeled On-Reflector Beam

Measured (Sky/Absorber)

BYURadio Astronomy Systems

Research GroupDual-Polarized Element Design

BYURadio Astronomy Systems

Research GroupFour Channel Downconverter Board

BYURadio Astronomy Systems

Research GroupGain and Phase Stability

BYU/NRAO goal: beam response stable to one part in 5e-4 (one hour integration at 1 kHz bandwidth)

PAF model simulations: this corresponds to 0.3 degrees relative drift

1200 1400 1600 1800 2000 2200-0.5

0

0.5

Time (24-hour)Cha

nnel

pha

se re

lativ

e to

refe

renc

e ch

anne

l (deSystem stability measurements (cov. matrix), Reference channel: 1

138 139 140 141 142 143-0.02

0

0.02

0.04

0.06

0.08

0.1

time

phas

e sh

ift re

lativ

e to

ele

men

t 1 (d

eg)

BYURadio Astronomy Systems

Research GroupBeam Calibration Lifetime

Beam pattern with fresh and stale (2 days) calibrations

BYURadio Astronomy Systems

Research GroupFocal L-band Array for GBT (FLAG)

X Engine: Correlator/Beamformer, Spectrometer, Pulsar

Array aperture, Antenna elements,LNAs, Cryo system,Down converters

•••

Sample clockfunction gen

and distribution

Ch. 1 ADC1 Gsps

ROACHFPGA

•••

1 TB SATARAID 0 Disk Array

Rack Mount PC

1 TB SATARAID 0 Disk Array

Rack Mount PC

20 p

ort 1

0Gb

Ethe

rnet

Sw

itch

Fujit

su X

G20

00 S

erie

s XF

P

F Engine:Direct RF sampling, digital down conversion and FFT

•••

•••

(× 10)

Attached PCs:System control and data storage(1/2 existing)

(×10)

(×10)

(× 40)

ADC1 Gsps

Ch. 4

ADC1 Gsps

ROACHFPGA

ADC1 Gsps

Ch. 40

ROACHFPGA

ROACHFPGA

(existing)

CX4 copper 10 Gbethernet links

LNA

Ant.

BPF

×

LO

Back End (Jansky Lab)Front End (GBT)

LNA

Ant.

BPF

×

LO

Signal Transport:Optical fiberand modems

BYURadio Astronomy Systems

Research GroupModeled GBT PAF Performance

Goal: One HPBW steering radius, 7 pulsar search beams

Effective F/D is 0.7 -> wider array requiredto illuminate dish

BYURadio Astronomy Systems

Research GroupModeled GBT Tsys

BYURadio Astronomy Systems

Research GroupFLAG Activities

PAF element design Cryostat, LNAs Signal transport (new fibers installed) Multichannel receivers Signal processing backend

– Calibration and beamforming algorithms– Pulsar search engine

Control software and data storage