A N A L I S I E M N U M E R I C A D I P U P I L L E T O R A L D O

P. B O L L I ( I N A F - O A A )

Super resolving systems: Toraldo Pupils (PUTO Project)

Villa Galileo, Firenze, 12 Ottobre 2017

AGENDA

• Tools: Software (FEKO) and hardware

• Problems encountered to match the EM simulations to the TP analytical

description and definition of the EM model

• Simplified model for describing the super-resolution with respect to the

analytical model

• Simulations for comparison with the anechoic chamber measurements

• Collimator for the Medicina radio telescope

• Continuous TP

FEKO 1/2

FEKO (from Altair) is a comprehensive computational electromagnetics

code used widely in the telecommunications, automobile, space and

defense industries.

The MoM is a full wave solution of Maxwell's

integral equations in the frequency domain.

“Source method" only the structure in

question is discretized

No boundary conditions

Memory requirements (N2) scale proportional to

the size of the geometry in question (N) and the

required solution frequency.

FEKO 2/2

• Planar Green Functions for Multilayered Media: Planar Green’s Function to model the aperture

• Surface Equivalence Principle (SEP): The SEP introduces equivalent electric and magnetic currents

on the surface of a closed dielectric body

• Higher Order Basis Functions (HOBF): use higher order polynomial basis functions to model the

currents on any particular mesh element. Such HOBF allow the user to mesh geometry with larger

triangles, while obtaining the same solution accuracy.

• Multilevel fast multipole method (MLFMM): The MLFMM differs from the MoM in that it groups

basis functions and computes the interaction between groups of basis functions, rather than between

individual basis functions. Memory requirement: N2 N*log(N)

• Distributed/Shared Memory Hybridisation Optimized

• Lua Scripting and Automation

HARDWARE

• Deskotp

Windows 7 professional (64 bit)

XEON E3-1275v2 (3.5 GHz) – RAM=32 GB / Core=4 / Threads=8

Single-user

• Workstation

CentOS 7 (64 bit)

2 x XEON E5-2680v2 (2.8 GHz) – RAM=64 GB / Core=20 / Threads=40 (max 32 due to the FEKO

license)

Shared-user

Workstation vs desktop: 3-4 reduction factor in the computational time (if 32 GB RAM is enough)

One network license (3 keuro/year) with no simultaneous use

DISCRETE TP: ANALYTIC MODEL

DEFINIZIONE MODELLO EM

• Onda piana incidente soddisfa la condizione di fase, ma crea problemi di

diffrazione dal bordo esterno del disco metallico

• Si è quindi passati alla sorgente SWE (espansione onda sferica) gaussiana

(-14 dB @ 21.4 gradi). La sorgente deve essere posta lontana per avere

una quasi-onda piana nella PT, ma non troppo per non sovra-illuminare il

bordo

• Si è infine consolidata la soluzione del planar multi-layer

substrate con onda piana

ALTRI PARAMETRI EM • Frequenza 20 GHz miglior compromesso tra dimensioni fisiche contenute e

tempi di calcolo non eccessivi. Inoltre strumentazione RF presente in laboratorio

• Oggetti dielettrici (TP e lenti) di polietilene: costante dielettrica 2.278 e zero perdite ohmiche

• Inversione di fase (ritardo 180 gradi): spessore dielettrico circa l

• Conduttori elettrici perfetti

• Moarse mesh (λ/8)

• Onda piana polarizzata linearmente

• Laddove possibile utilizzati piani di simmetria elettrico e magnetico

• Pattern ottenuti in far-field o near-field (o matrice di scattering)

TP3

TP4

MODELLO SEMPLIFICATO TP3 • Principio sovrapposizione del campo irradiato da ciascun anello

• Approccio ha permesso di comparare simulazioni con modello teorico

• Inoltre considerare apodizzazione e tunare la fase della PT

R=1.5 cm

Fase = 0 deg

Amp = 1 V/m

Ri=3 cm; Re=4.5 cm

Fase = 0 deg

Amp = 1 V/m (0.23 V/m)

Ri=1.5 cm; Re=3 cm

Fase = 180 deg

Amp = 1 V/m (0.63 V/m)

RISULTATO TP3 - fase ideale

Rossa: teoria

Nera: FEKO

TP3 - fase con

dielettrico

Rossa: teoria

Nera: FEKO

1.7 cm

No apodizzazione Con apodizzazione

RISULTATO Ottimizzazione

spessore dielettrico

della corona 1 della

TP4

LABORATORY MEASUREMENT

EXP. ASTRONOMY RESULTS 1/2 Camera anecoica di Arcetri

Linear scanning in near-field

Matrice di scattering senza «probe compensation»

Misure

senza TP3

Misure con

TP3

FEKO

con TP3

Fig. 7, Exp Astron (2017) 43:285–309

EXP. ASTRONOMY RESULTS 2/2 Camera anecoica di IFAC

Plane-rectangular NF-FF transformation (UNISA)

Simulazioni FEKO in FF

Figs. 13 e 14, Exp Astron (2017) 43:285–309

NOT-NORMALIZED PATTERN & TP4 ISSUE TP4 invertita

(in accordo a teoria)

TP4 misurata in lab

COLLIMATORE PER MEDICINA

Aperture excitation (corresponding to the

Cassegrain focus): the focal plane field produced by

a plane wave reflected by the Medicina primary

mirror

First lens to convert the sphercial wave to a plane

wave

Aperure with Toraldo Pupil

Second lens to convert the plane wave to a

sphercial wave towards the new focus

New focal position

PIANO TP

52.5 42 21 8.75 52.5 42 21 8.75

PUPILLA CONTINUA

CONCLUSIONS

• Quite good knowledge of FEKO and specifically of this specific problem

• Nice tool for better understanding the physics behind the model and

predicting possible problems in the experimental set up (especially in view of

the installation at the Medicina RT)

• Simulation data have contributed in publishing the TP results

• Workstation very useful to run simulations in a reasonable time

• More systematic approach