AAVP Workshop December 2010 TITLEAAVP Workshop December 2010 Aeff/Tsys evaluation for AAlo sensors Cambridge 8th-10th December 2010 Federico Perini 1,

AAVP WorkshopDecember 2010 TITLE AAVP WorkshopDecember 2010 Aeff/Tsys evaluation for AAlo sensors

Aeff/Tsys evaluation for Aeff/Tsys evaluation for AAlo sensors AAlo sensors

Cambridge 8th-10th December 2010

Federico Perini1, Jader Monari1, Giuseppe Virone2, Pietro Bolli3

1 INAF/IRA-Medicina radio telescopes2 IEIIT/CNR-Politecnico di Torino

3 INAF/Osservatorio Astronomico di Cagliari


G. Cortes Medellin, “Antenna Noise Temperature Calculations,” SKA Technical Memo Series n° 95

White paper on the antenna sub-systems for the SKA project: P.D. Patel, “Antenna Concepts Consideration for SKA”, part of

the SKA memo 91, “An SKA Engineering Overview” by P. Hall

Compare different Compare different antennas?antennas?


0,0,2

0 0 0

0,0,2

; , ; , sin

; , ,; , sin

n b

ant

n

P T d d

TP d d

General formulation:

where Pn(v;) represents the antenna radiation pattern and Tb(v;’’), the brightness temperature distribution (here Tb(v;’))

Direction in the azimuth plane

Zenith

Horizon

Antenna TemperatureAntenna Temperature

Pn computation is demanded to an external EM Antenna CAD (GRASP, CST,…) whereas Tb is evaluated by the Matlab code itself


Two different coordinate reference systems: Pn is defined respect to the one related to the antenna itself (z axes = main beam or pointing direction) whereas Tb is defined respect to the Earth (z’ = local zenith)

0 0 0

0 0 0

, , , ,

, , , ,

To compute the integral we need only one coordinate system, so we need the conversion from one to another:

0 0 0arccos sin sin sin cos cos

0 0 0 0 0 0 0

0 0 0 0 0 0 0

sin sin sin cos cos sin sin cos sin cosarctan

cos sin cos sin cos sin sin sin sin cos

Coordinate reference systemsCoordinate reference systems

Ground

Zenith

Circumferenceat fixed correspond to several values of


The brightness temperature can be split in 2 main contributions:from sky (0° < ’ < 90°) and from ground (90° < ’ < 180°)

; ; , 0 90; , ;

; ; , ; ; , 90 180

skyb n

n bb b

T PP T

T P T P

1 1 1

1 1 1

; ; ; 1

; ; ; 1

sky gnd skyb b gnd

sky gnd skyb b gnd

T T T T T

T T T T T

2 2

2 2

1 2 1 2 1 2 1

1 12 2

1 2 1 2 1 2 1

cos sin cos sin;

cos sin cos sin

Moreover the contribution from the ground (emission and scattering), is a polarization dependent process:

Ground contributionGround contribution


The Tb model is the one proposed by [Cortes], which includes the effects of the absorption coefficients of water vapour and oxygen, the CMB and the emission from the galaxy

,

2 2,

0,

0 ,

20

; ;;

1 sin 1

a

a

zh

H O O atmhsky

b bo

e

k z k z T z eT T e dz

z r

0obo CMB gT T T

Tgo and are function of the observed sky region

[Cortes] suggests reasonable values as:

Tgoe

Zenithal opacity

Atmosphere temperature

Effect of Earth curvature

Brightness TemperatureBrightness Temperature


Tb calculatorTb calculatorftp.ira.inaf.it/pub/outgoing/fperini/


Ta calculator example 1: Ta calculator example 1: BEST-1 @ 408MHzBEST-1 @ 408MHz


Ta calculator example 2: Ta calculator example 2: 32mt VLBI Dish @ 22GHz32mt VLBI Dish @ 22GHz


AAlo Vivaldi antennaAAlo Vivaldi antenna

Vivaldi Antenna, f=450MHz, 2=3.5Pn resolution, (deg)

Ta (K) Tagnd (K) Tasky (K) Time comp. (min)

2.5 69.4 52.4 17.0 135 69.1 51.6 17.5 3.5

Pattern at fmax=450MHz

For BEST-1 Tcomp=150 min,using two different spacing for

Pn, fine (0.04°) for the main beam and coarse (0.68° )

outside the main beam


AAlo Vivaldi antennaAAlo Vivaldi antenna


TTRECREC??50Ohm 75Ohm

Trec = TLNA = 30K @ 300K seems reasonable


RECK

a

Keff

TT

A

)1(

)1(2

2

AntLNA

AntLNAK

ZZ

ZZ

*

Aeff/Tsys?Aeff/Tsys?

RECa

elemelemeff

SYS

eff

TT

NA

T

A

_


Aeff/TsysAeff/Tsys


Double size antenna?Double size antenna?

(Aeff/Tsys)2/(Aeff/Tsys)1

Freq [MHz] theta=0°(zenith)

theta=45°phi=90°

theta=45°phi=0°

70 0.84 1.12 0.87120 1.59 0.82 1.79260 1.74 2.97 0.47450 0.93 1.83 1.11

Freq (MHz) Tant 1 [K] Tant 2 [K]70 1785 1879

120 484 530260 112 105450 67 58


Future worksFuture works• Tb(v;’) Tb(v;’’)

• Considering the coupling effect

• Take in account the array factor at station level (antennas positioning) and at full array level (stations positioning)

Stronger collaboration with all partners involved in this task

Thanks!

Documents

AAVP Workshop December 2010 TITLEAAVP Workshop December 2010 Aeff/Tsys evaluation for AAlo sensors Cambridge 8th-10th December 2010 Federico Perini 1,