PG. Wiid - Electromagnetic Simulation Tools for

Electromagnetic Simulation Tools for MeerKAT

PG Wiid

Stellenbosch University

South Africa

CHPC National Meeting and Conference

Cape Town, South Africa 2013

On The Menu • Background

• Introduction

• CHPC Research Areas

• Antenna Characterisation

• MeerKAT Scale Modelling

• Future Work

• Conclusions

• Acknowledgements

CHPC National Meeting and Conference 2013 2

Background • Square Kilometre Array or SKA

• South African Demonstrators KAT-7 and MeerKAT

• Geographical advantage led to Radio Astronomy Reserve proclaimed by government

• Radio environment protected from 70 MHz up

• Radio frequency interference (RFI) need to be measured and monitored


Introduction • RFI measurements over wide band required multiple

antennas transported to site

• Bulky and heavy, need for alternative antenna

• 50:1 BW PCB-LPDA developed from 160 MHz to 8 GHz

• To use successfully, needs full characterisation

• Environmental RFI from lightning ongoing research

• MeerKAT design inputs on lightning protection


CHPC Research Areas Two major research areas on CHPC:

1. Full Antenna Characterisation – Antenna Measurements

– Reflection coefficient, gain and antenna factor

– FEKO CEM model validation with measurements

– Antenna pattern from simulation

2. MeerKAT Dish Scale Modelling – Simplified physical scale model of MeerKAT design as at

end of 2012

– CEM model in FEKO for lightning induced current investigations

– Model validation with measurement in anechoic chamber


Antenna Measurements • Main measurement interest for:

– Antenna gain

– Antenna factor

– Reflection coefficient

• SU Engineering building roof measurements 50MHz to 3.6GHz

• Anechoic chamber measurements from 50MHz to 8GHz

• Open area test site (OATS) measurements with time-gating from 10MHz to 8GHz

• Measurements show repeatability


Antenna Modelling in FEKO • Full characterisation of antenna possible in CEM

• FEKO Method of Moments (MoM) CEM commercial code

• PCB-LPDA initial modelling on desktop not sufficient

• Specific detail required for feed-tab at tip of antenna, especially at high frequency

• MoM surface mesh discretisation in triangles to solve Maxwell’s equations for currents and electric fields

• Progressively finer mesh used toward feed < λ/10


FEKO on CHPC • 550 MHz implied mesh of 48,697 triangles in free space

• Required 118 GB RAM to solve matrix equations

• 10 Nodes on Dell Cluster available to SU for FEKO installation, 6 nodes used for antenna simulations

• 24 cores used with total 210 GB RAM available

• 50 MHz to 300 MHz – 50 frequency points calculated

• Each frequency point took 1 hour to calculate

• 300 MHz to 550 MHz – 25 frequency points calculated

• Each point took 4 hours to calculate with finer mesh

• Total simulation time – approximately 150 hours


Antenna Gain Results


Radiation Pattern & Currents


MeerKAT Model in FEKO • Simplified 1/20th scale model of MeerKAT design (end

2012) used for CEM model validation

• Injection port and two “earth” measurement ports

• S-parameter measurements from 45 MHz to 9 GHz in anechoic chamber for validation

• 1/20th scale CAD-model imported in FEKO

• Multiple interconnection problems…


Final Dish Model in FEKO


• Loss of interconnection showed on reflection parameter at injection port as compared to measurement

• Continuous adjustments made to ensure connections in model after each 2-day run

• Final model: – 67,057 triangles and 101098 unknowns to solve

– Required 210 GB RAM

– Used 4 cores and full 35 GB RAM

each on 6 nodes of DELL cluster

– 162 frequency points up to 3.6 GHz

– Average 2.2 hours per frequency

– 356 continuous hours

Dish S-Parameter Results


• Larger memory requirement for higher frequencies for antenna characterisation

• Dish modelling of receiver detail in simplified model

• New design simplification for accurate current path studies, model already imported

• Interconnections again major part of work

14 CHPC National Meeting and Conference 2013

Future Work

• CHPC pivotal in antenna characterisation

• Simulation and measurement agreement made it possible to obtain vital information through simulation, otherwise non-trivial to obtain with measurement

• MeerKAT dish scale model validation (mostly) done, but the design has changed with the evolving project

• New design will be simplified for further studies on current paths and possible RFI hardening


Conclusions

Acknowledgements • SKA South Africa and NRF for Funding

• CHPC of CSIR and Sticks Mabakane for support

• EMSS SA for FEKO and Danie Ludick for support

• David Davidson for job submission tips

• Denel Houwteq OATS and Anechoic chamber, specifically Fred Thomas for support

• Measurement support – Howard Reader, Rob Anderson, Antheun Botha, Nardus Matthysen, Nezmi Tezel


References • [1] Wiid PG, Palmer KD, Van Der Merwe PS, Reader HC. A Practical 50:1

Bandwidth PCB-LPDA Antenna for MeerKAT RFI Studies. 14th International Conference on Electromagnetics in Advanced Applications ICEAA'12, Southern Sun Cape Sun Hotel, Cape Town, South Africa, IEEE 2012: 965-968.

• [2] Wiid PG. Lower Uncertainty PCB-LPDA Antenna Measurement on Open Area Test Site. 15th International Conference on Electromagnetics in Advanced Applications and Electromagnetic Metrology Symposium ICEAA and EMS '13, Torino Incontra Congress Centre, Torino, Italy, IEEE 2013.

• [3] Wiid PG, Reader HC, Geschke RH. Karoo Array Telescope: Lightning Protection Issues and RFI. 30th International Union of Radio Science General Assembly and Science Symposium URSI GASS, Istanbul Convention and Exhibition Center, Istanbul, Turkey, URSI 2011: 1-4.

• [4] Wiid PG, Reader HC, Geschke RH. Radio Frequency Interference and Lightning Studies of a Square Kilometre Array Demonstrator Structure. IEEE Transactions on EMC, 2011; 53(2) : 543-547.


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PG. Wiid - Electromagnetic Simulation Tools for