KAT7 Antenna DevelopmentWillem Esterhuyse

MeerKAT Project Manager

(Subsystem manager: Antenna Structures)

esterhuyse@gmail.com

083 447 1615

Introduction

• Introduction

• Technical focus (last year - XDM)

• Process/Strategy

• Touch on Progress

• Antenna Development Phases/Goals

• Basics (and did we follow them)

• XDM/KAT7 (one piece composite)

• Detail

• Progress

• Optimize performance/cost

• Conclusion

Antenna Development Phases/Goals

XDM (Done)

Design Optimization(Done)

KAT7 – Manufacture started

MeerKAT

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GOAL

• Cost effective antenna for

MeerKAT

• Costed antenna option to

which we own the IP that

would be considered as an SKA

option

Main Specifications and Design Goal XDM

KAT7Spec Achieved

Pointing Accuracy (deg) 0.04 25” RMS 25” RMS (target 15)

Surface Accuracy (mm rms) 4 1.8 1.5 (target 1)mm

Frequency Range (MHz) 700 - 1700 Up to 8 GHz Up to 8 GHz

Wind (Operational) km/h 20 36 36

Wind (Marginal Operation) km/h 36 45 45

Wind (Drive to Stow) km/h 36 55 55

Wind (Survival) km/h 160 160 160

Azimuth Rotation speed (deg/s) 1 2 2

Elevation speed (deg/s) 0.5 1 1

Diameter 15 15 12

F/D 0.5 0.5 0.38

Lowest Natural Frequency (Hz) 3 3+ 3+

Feed Mass (kg) 200kg with rotator 75kg no rotator

Mount Type All-Az Alt-Az

Project Basics

• Development projects (any project) need

• Good Upper and Project Level Management

• Culture/support

• Good process (coupled with a healthy dose of common

sense)

• Apply to system and subsystems

• System Engineering tailored to your project/people

• Interfaces/Responsibilities clearly defined

• Good people (most important) – think marriage

• Any project need a Champion/Champions

• Attitude/Domain Specialist

• Experience (innovation vs. apply existing technologies/techniques)

• Design/Analyses and others

• Diligent

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Luck – “I’ll be lucky rather than good any day ”Gary Bevilacqua (Caterpillar)

“Better is the biggest enemy of good enough”Kobus Meiring (SALT)

Applied to Antenna SS

Basics – Process

• Simple process – question is how well you execute it

• There will often be pressure not to follow this – tailor to your

system, but understand risk of omitting stages (and live with it)

• Things get tight – following is neglected

• Design Review and Acceptance testing

• System Integration/Operation hampered by unreliable subsystems

User requirements definition

User spec (reviewed/signed off)

System design & modeling (trade-offs)

System spec (reviewed/signed off)

Sub-system design & prototyping (trade-offs)

Sub-system spec (reviewed/signed)

Component spec

Operational testing

System int & test

Sub-system int & test

Detail design, design reviews, acceptance

testing definition, datapacks, manufacture

Component int & test

Verification

Verification

Verification

Validation

Basics – Design Reviews

Why Design Reviews are critically important

Basics – Acceptance Testing• Example of VCRM on XDM – 130 requirements that required testing

• Difficult to test all requirements for all possible events

Section in spec. Section

Test Level

Test Method Reference

Approval Note

Approval/

Date

aThe estimated mass of the structure is TBD kg (excluding the controls and drives). N/A N/A N/A N/A N/A N/A

b

The lowest natural frequency of the structure shall be more than 3 Hz, analyzed with the weight of the FPA (see 5.2.1.3) included and making provision for electrical and control cabling and cabling duct weights, the routing of which is TBD. System

Analysis, Test

5.15 (Control Test) and KAT7200PR1007-0037002

Issue 1 (FEA Analyses) Pass

FEA Analyses lowest frequency 4.2 Hz excluding servo's. Azimuth 2.4 Hz,

Elevation 3.5 Hz - this include drivetrain stiffnesses, but is

included as info..  6.2.1.1.3Wind Loads and Deflections N/A N/A N/A N/A N/A N/A

aThe operating wind speed is given in Table 2 in section 5.3.2.1. Info Info Info Info Info Info

6.2.1.1.3.2

The wind loading as a result of this wind speed, combined with gravitational and thermal effects and manufacturing and alignment inaccuracies shall not cause reflecting surface inaccuracies of more than the value specified in section 6.2.1.8.2. Info Info

KAT7200TP2000-51002 Issue 1 par 3 / 6.2.1.8.1.g Info    

6.2.1.1.4Tolerances N/A          

6.2.1.1.4.1

The required accuracy of the reflecting surface shall be 4mm RMS (target of 2mm RMS) or better and 6mm maximum (target 3mm) - this shall include gravity, thermal and wind influences (operating wind speed - see section 5.3.2.1 - in any position) as well as manufacturing and alignment inaccuracies. Info

Analyses, Measure

KAT7200TP2000-51002 Issue 1 par 3 / 6.2.1.8.1.g/h Info    

aThe survival conditions are given in Table 4 in section 5.3.2.3. Info Info Info Info Info Info

b

The surface errors shall be measured relative to the best fit parabola, y=(x2+z2)/(4*fd) where "fd" is the focal distance (7500mm), and the FPA displacement (see section 6.2.1.9) shall be calculated relative to this parabola. Info

Analyses, Measure

Measurements was done relative to best parabola with

variable focal length as discussed with Mike Gaylard. Info Info  

cThe variations in surface accuracy shall not be systematic (variations shall be random). System Review KAT7200PR1003 Variation

Slight systematic variations, but that does not appear to impact on the performance. See NRF-XDM-0.0-TR0013.  

6.2.1.1.5Lightning Protection N/A N/A N/A N/A N/A N/A

aThunderstorms occur on the site so the antenna must be equipped with a lightning protection system. System Inspection

MESA report - HartRAO XDM visit 18 July07 Pass    

bA spike shall be placed at the FPA System InspectionMESA report Hartrao XDM 18

July 2008. Variation

Direct Strikes on XDM very unlikely (26m has not had one

and is much higher) - the MESA report therefore caters

mostly for indirect strikes.  

People

• Project Time pressure – subcontract structural design

manufacture

• Antenna Structure – tender (IST(BAE)) – XDM/KAT7• Dish – MMS

• EM design – EMSS• Feed into specification + design reviews

• Lightning/RFI – MESA (Prof HC Reader + students)• Feed into specification + design reviews

• HartRAO - Dr. Mike Gaylard/Dr. George Nicholson/Prof. Roy Booth

• Director Science/Engineering – Prof. Justin Jonas

• Experience

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People – Antenna Structures - IST

XDM

• IST Dynamics (now BAE)

• Prime contractor XDM – open Tender

• High tech electro-mechanical systems + software

• Military is biggest client

• Antennas – apply existing knowledge/expertise• Reduced risk

• Experience working with them?

People – Antenna Structures - BAE

KAT7

• BAE (previously IST Dynamics) – open Tender

BAE GD SatCom Cobham/ Patriot

People – Dishes - MMS

• MMS

• Subcontracted by IST/BAE

• Dish construction and design

• Exceptional experience in Composite

design and manufacture

• Existing for more than 20 years

• Antennas – apply existing

knowledge/process

• Reduced Risk *Work Ethic

People – EM Design - EMSS

• Optical design (dish shape)

• Tolerances

• Feed leg shape/details

• Deflector

• It’s in the detail

People – MESA

• Lightning/RFI – MESA (Prof Howard Reader)

• Fundamental Understanding – NB for flame sprayed dish

• Scale model – verify analyses results

• Build understanding/Confidence

XDMVisual Recap – detail and lessons learned

shown under KAT7

KAT7

ANALYSES - CFD

• Detailed CFD (Computational Fluid Dynamics) analyses

to determine pressures on dish as result of wind

loading (for use in FEA analyses)

• Results compared to published results – good correlation

• Results compared with limited experimental data – good

correlation

Analyses - FEA

Mode

1:

4.51 Hz

Mode 2:

5.5 Hz

ANALYSES - MODAL

ANALYSES - CADFEKO

• Lightning/RFI – MESA (Prof Howard Reader)

• Fundamental Understanding – NB for flame sprayed dish

• Scale model – verify analyses results

• Build understanding/Confidence

Experiments – Pointing/Temp• Steel Pedestal

• Measure Existing steel

pedestal

• Paint heat performance

• Result – Paint selected +

Sunshield

• Temp sensors

Integration before going to Site

• Industrialization version

• PTA in BAE parking lot

• Minimize time/integration on

site

• Control loops

• Cables

• Catch manufacturing issues

early

• Trial assembly

• Simulate dish influence

• 3x counterweight frames

KAT7 Improvements (from XDM)• Mould

• Pattern Aluminium (KAT7) vs. Wood

(XDM)

• Mould Setup/Conditions

• Improved surface accuracy

• Analyses

• Thermal design improved (thin open

sections)

• FEA - Increased stiffness

• Dish surface error less

• Feed displacement less

• Better pointing

• EM design

• Dish shape optimized (for single pixel

feed)

• Cone Deflector improved detail

• Feed leg shape optimized (including

structural)

• RFI/Lightning protection design

improved

• Control system improved

Mould

• Practical Lessons learnt

XDM

• Setup

• Dish off mould

• Process proven XDM

• KAT7 conditions more

controlled, more

accurate mould

• Result TBD, but

HOT OFF THE

PRESS

Control

Pedestal Layout

Conclusion• Development of low cost dish for KAT7

• Define sensible stages

• Good process

• SE, design reviews, testing

• Good people / detail orientated

• Dedicated, competent

• Analyses, Experiments, Scale models

• Common Sense prevailed (mostly )

• Low cost Poor performance (Improve XDM)

• Remaining work• Complete KAT7

• MeerKAT

• MeerKAT Detail design (changes from KAT7 )

• Another prototype might be required

• Manufacturing processes (optimize cost)

• MeerKAT (and SKA )