SKA DISH ELEMENT TECHNICAL SOLUTION

Transcription

1 SKA DISH ELEMENT TECHNICAL SOLUTION Document number... SKA TEL.DSH.MGT CSIRO TS 004 Revision... 1 Author....SKADC Consortium Date June 2013 Status... Released Name Designation Affiliation Date Signature Submitted by: C. Jackson On behalf of SKADC consortium CSIRO 7 June 2013 Accepted by: Approved by: Thursday, 06 June 2013 Page 1 of 48

2 DOCUMENT HISTORY Revision Date Of Issue Engineering Change Number Comments A Full draft release for SKADC review Released for RFP submission DOCUMENT SOFTWARE Package Version Filename Wordprocessor MS Word Word 2010 SKA TEL.DSH.MGT CSIRO TS 004_DishTechSol Block diagrams Other ORGANISATION DETAILS Name Registered Address SKA Organisation Jodrell Bank Centre for Astrophysics Room Alan Turing Building The University of Manchester Oxford Road Manchester, UK M13 9PL Registered in England & Wales Company Number: Fax +44 (0) Website Thursday, 06 June 2013 Page 2 of 48

3 TABLE OF CONTENTS DOCUMENT HISTORY... 2 DOCUMENT SOFTWARE... 2 ORGANISATION DETAILS... 2 TABLE OF CONTENTS... 3 LIST OF FIGURES... 5 LIST OF TABLES... 5 GLOSSARY INTRODUCTION Purpose and Scope of this document Review of SKA RfP Baseline & this Technical Solution Validity and basis of the Technical Solution as derived in the SKADC Work Plans SKADC TECHNICAL SOLUTION FOR DISH SPECIFICATION DISH Context DISH Optics DISH Structure & Performance SINGLE PIXEL FEEDS SKA_mid Band 1 Feed Package Band 2 Feed Package Band 3, 4 and 5 Feed Package FEED PACKAGE SKA1_survey RECEIVER PACKAGE SKA_mid RECEIVER PACKAGE SKA1_survey POWER Local monitor and control LMC implementation IMPLEMENTATION ESTIMATES FEED PACKAGE SKA1_mid SKADC Technical Solution Estimates SKA1_Survey SKADC Technical Solution Estimates SKADC Technical Solution Antenna Sub System(s) RECEIVER PACKAGE SKA1_mid SKADC Technical Solution Estimates SKADC Technical Solution Antenna Sub System(s) RECEIVER PACKAGE SKA1_mid SKADC Technical Solution Antenna Based Support Systems Estimates Thursday, 06 June 2013 Page 3 of 48

4 4 REFERENCES APPENDIX A A1.1. Introduction Designing the SKA optics A1.2. Optics parameters and options A1.3. Initial reduction of the parameters A1.4. Selection of the dish design sets A1.5. Restrictions A1.6. Determine the evaluation criteria A1.7. Optics design candidates A1.8. References for Appendix A1 Designing the SKA optics Thursday, 06 June 2013 Page 4 of 48

5 LIST OF FIGURES Figure 1 CAD model of Eleven Feed for GHz band Figure 2 MeerKAT L Band Receiver (left) with cryogenic waveguide load Figure GHz LNA MMIC and assembled demonstrator module Figure 4 Measured gain and noise temperature of the demonstrator module Figure 5 Block diagram of the SKA_mid receiver package Figure 6 Block diagram of the SKA1_survey receiver package Figure 7 Outline of LMC system Figure 8 Outline of SKA1_mid Feed/LNA and receiver system Figure A1 1: Definition of the parameters describing the offset Gregorian dishes Figure A1 2: Schematics of the selected optics design sets LIST OF TABLES Table 1 Summary of the most important Dish Performance Requirements Table 2 Summary of the most important Dish Performance Requirements Table 3 Summary of the most important SKA1 Mid Array requirements Table 4 Summary of specifications for the LNA module for the Band 3 receiver Table 5 Summary of the most important SKA1_Survey Array requirements Table 6 Summary of the most important SKA1_Mid Array requirements Table 7 SKA1 Receivers Technical Solution Bands 1 5a Table 8 SKA1 Receivers Technical Solution Bands 5b 5d Table 9 Summary of the most important SKA1_Survey Array requirements Table 10 SKADC Feed package Estimated requirements Table 11 SKADC PAF Feed package Estimated requirements Table 12 SKADC Receiver antenna sub systems Estimated requirements Table 13 SKADC Receiver technical solution antenna based support systems Table A1 1 Dish design options with target reflector sizes for each design Thursday, 06 June 2013 Page 5 of 48

6 Definition of terms: GLOSSARY SKA Baseline The SKA specification (baseline) as issued with the RfP and as set out by the SKAO. SKADC The SKA Dish Consortium comprising institutes, industry and other stakeholders. SKADC Technical Solution The SKA Dish Consortium s response to the SKA Baseline, as submitted as part of the SKADC response, based on reasoned discussion of technologies able to at least meet the SKA Baseline. Feeds & LNAs Feed system and low noise amplifier (LNA). Feed package The item responsible for converting incident radiation to signals in co axial cables. This includes, feeds, LNAs as well as packaging and control and monitoring. Receiver Everything post LNA (except possibly a second stage amplification in the feed package) including analog todigital conversion (A/D), gain, RF and (any supporting) digital systems ahead of the correlator. SKA Element Level 3 item in the WBS e.g. Aperture Array, Dish, Science Data Processing. SKA sub system Level 4 item in the WBS, e.g. a major part of the dish element e.g. Dish Structure Thursday, 06 June 2013 Page 6 of 48

7 1 Introduction SKA TEL.DSH.MGT CSIRO TS 004 This Technical Solution captures the SKADC s response to the SKAO Baseline issued at RfP. As requested in the SKA Request for Proposals [1], this technical proposal for Dishes summarises: The functional descriptions of the Sub systems that comprise the Dish Element Key component characteristics Performance analyses against the requirements Key Element Level requirements 1.1 Purpose and Scope of this document The SKADC Technical Solution is a major part of our RfP response and has formed the framework from which we have defined our work plans. In considering system optimizations during the work of the pre construction phase, we aim to deliver a superior, well engineered system. SKADC Technical Solution described in this document is aligned to the baseline design and is achievable on the SKA1 project timeline. This Technical Solution will be used by SKADC from the start of pre construction. This Technical Solution, plus the concept of operations (ConOps) and further requirements definitions (including interface control document (ICD) clarifications) will be reviewed by SKADC (with SKAO) as we develop a full set of Requirements Specifications. Development of the full Requirements Specifications is planned to occur in September 2013, and will be led by the SKADC Systems Engineering team. The Technical Solution will be updated and we suggest it be used as an informal description of the SKADC (dish) implementation that reflects the Requirements Specifications. The Technical Solution addresses all aspects of the baseline and sets out procedures to refine the selection of e.g. feeds, dish (optics), cryogenics systems, etc. to meet the intended SKA specifications. In deriving the Technical Solution the underlying philosophy has been to design for the production of thousands of units. The SKADC will consider options and alternatives, particularly during Stage 1, ahead of the Preliminary Design Review (PDR). The imperative to deliver the Critical Design Review (CDR) will mean that the focus will be on a well engineered, robust system covering all necessary aspects. In terms of pre construction planning, the SKADC has made some early estimates of the physical implementation (e.g. mass, size of feeds and their combinations, location of equipment, etc), which are captured in Section 3 of the Technical Solution. Major changes to the SKADC Dish Technical Solution, which are expected to be improvements over the first outline, will be agreed in conjunction with the SKAO Engineering team with suitable justification materials (analyses, performance measures, etc.). The SKAO RfP Baseline does not detail the optical design of the dish. As this is a critical component that is required ahead of the full mechanical design of the dish, feeds etc., Appendix A1 sets out the analyses that will be used to derive the SKA dish optics design. The outcome of this process will be both the dish optics and optimised feeds (the illuminating part only, not fully packaged feed and LNA systems) for each of the respective bands. The material in the Appendix is treated as a stand alone, self contained document with its own references. The way in which this process is to be carried out by SKADC is described in the Work Plan. Thursday, 06 June 2013 Page 7 of 48

8 1.2 Review of SKA RfP Baseline & this Technical Solution SKA TEL.DSH.MGT CSIRO TS 004 For each SKADC sub system, the Technical Solution begins by reproducing the SKA RfP Baseline extracted from [5], re stated in boxed text. In most cases, this will be a verbatim quote from [5]; however, in some instances, the expertise of the SKADC has been used to interpret the spirit and intent of the RfP Baseline. The following text, in each section, then describes the requirements and specifications that the SKADC considers are most appropriate for a practical dish system that will go the closest to achieving the SKA RfP Baseline. 1.3 Validity and basis of the Technical Solution as derived in the SKADC Work Plans Given all the above, and a number of face to face discussions at organisational and Work Package level, the SKADC has given due consideration to the Technological Readiness Levels (TRLs) and Risks of the Technical Solution proposed herein. The TRLs and Risks are described in detail in the SKADC Work Plans. Thursday, 06 June 2013 Page 8 of 48

9 2 SKADC Technical Solution for Dish Specification 2.1 DISH Context The DISH Technical Solution has been developed during a series of meetings and teleconferences commencing with the DISH Consortium discussion held on February The SKA Dish Array Consortium considers the following technical solution is a practicable implementation that satisfies the SKA baseline design.. Design philosophy: design for thousands of units single dish design to accommodate both single pixel feeds for SKA_mid and phased array feeds for SKA1_survey. The design of both SKA_mid and SKA1_survey will allow for the build out to SKA2 including the interchange of single pixel feeds and Wide Band SPF (WBSPF)/ Phased Array Feeds (PAFs) at some time in the future. 2.2 DISH Optics RfP Baseline Reflector antennas are used for both SKA1_survey and SKA_mid. [5, Sect. 7] Ideally the same antenna will be used for both single pixel and phased array feeds. [5, Sect. 7] Some features of the SKA1 dishes may have to be altered to accommodate PAFs efficiently. It is conceivable that slightly different optical surfaces from the SKA1_mid dishes can be used for SKA1_survey, while sharing the mechanical structure and the local dish infrastructure (mount, foundation, control, etc.). Significant investigative effort is still needed to determine whether PAFs can be combined efficiently with offset Gregorian dishes. [5, Sect. 9.2] The selected antennas are 15 m projected diameter, offset Gregorian optics. [5, Sect. 7] Designed for very high A e /T sys per unit of currency. The following are important qualitative characteristics required for SKA1 antennas [5, Sect. 7]: Smoothness of response in spatial and spectral dimensions, as limited by fundamental physics (e.g. edge diffraction). Scattering objects tend to generate low level resonances, which will have relatively fine frequency structure and/or chromatic sidelobes. Space at the focus for five independent receivers. Very low sidelobes beyond the first one. Excellent polarisation performance. Circular beam. Excellent performance down to ~450 MHz, good performance to 350 MHz. Excellent performance to 15 GHz, good performance to 20 GHz. Thursday, 06 June 2013 Page 9 of 48

10 Equivalent physical aperture 15 m diameter Low Frequency 350 MHz High Frequency 20 GHz Optics Clear aperture Efficiency >77 % 65% at 400 MHz and 20 GHz Total spillover noise 3 K L band Other losses <2 K L band 1st sidelobe 21 db Far out sidelobe level < 50 db Polarization purity 30 db Within HPBW Beam symmetry TBD Table 1 Summary of the most important Dish Performance Requirements Extracted from [5, Sect. 7, Table 5]. SKADC Technical Solution The following were agreed as an appropriate baseline SKADC Technical Solution: 15 m diameter, offset Gregorian dish with clear unobstructed optics; [5, Sect. 7] See the list of parameter sets in Appendix A1. f/d (eff) =0.5 f/d (eff) =0.5 is a compromise between a shorter f/d that is optimum for smaller feed sizes and smaller phased array feeds, and a longer f/d that is optimum for ease of dish optics design. This parameter will be investigated in the first phase leading to the optical down select. Support bore sight and off axis 6x6 beams; The dish optics needs to accommodate the baseline phased array feeds, which have 36 beams especially to achieve good performance for all 36 beams at the centre of the SKA1_survey Band 1, that is, ~600 MHz. This may require a sub reflector that extends beyond the standard geometrical optics boundaries. 6 m secondary; The sub reflector must be large enough to be a reasonable reflector at the low frequency (350 MHz) end. The initial estimate is that it would need to be of the order of 6 m in diameter. Any extensions for spill over shielding or supporting off axis beams will be included in this dimension (i.e. the effective sub reflector will be slightly smaller). Unshaped reflectors The baseline optics will be unshaped, primarily because shaping the optics deteriorates off axis PAF beams and unshaped optics are less feed pattern specific. This will, however, be investigated during the initial optics selection process once a set of optimal feed patterns for the same unshaped geometry is available. 1st sidelobe: 21 db; Far out sidelobe level < 50 db [5, Sect. 7] This only has an impact on the dish structure when shaping the reflectors. Surface rms (both primary and secondary reflectors) less than 0.5mm Thursday, 06 June 2013 Page 10 of 48

11 With the same feed art that achieves an efficiency of 0.77 in L band, the surface error efficiency has to be less than 0.84 to achieve a 0.65 overall efficiency. At 20 GHz, this translates to an effective surface accuracy of 0.5 mm RMS. Such surfaces are routinely achievable for a 15 metre dish. Feed mount high ; The DVA 1 investigation resulted in a severe cost penalty for the feed low configuration. Thus the feed high configuration will be the baseline proposal. It should be noted that the feed low configuration can be better shielded for spill over and allows much easier feed access for maintenance purposes. Hence both options will be considered during the optics selection phase. Reflector construction carbon fibre composite It was agreed that the reflector construction, for the baseline specification, would be carbon fibre composite. However, studies of steel/aluminium options should be undertaken as the baseline specification of composite still needs to be substantiated as the optimum solution (and this is the only case where the SKA Baseline appears to specify the material, which is strictly an implementation choice). The more appropriate high level requirement would consider the implications of reflectors made from panels (typical with aluminium and steel constructions) as opposed to single piece reflectors. All feeds shall be located at the secondary focus; The baseline SKADC Technical Solution specifically excludes the option of feeds being swung into the primary focal region of the primary reflector. Single feed indexer design: minimum of 5 feed positions selectable; Rotary indexer Same feed indexer design is to be used for both the single pixel feeds for SKA_mid and for the phased array feeds for SKA1_survey. The feed indexer design shall be rotary not a linear feed translator. 2.3 DISH Structure & Performance RfP Baseline Reflector antennas are used for both SKA survey and SKA mid. [5, Sect. 7] Ideally the same antenna will be used for both single pixel and phased array feeds. [5, Sect. 7] Some features of the SKA1 dishes may have to be altered to accommodate PAFs efficiently. It is conceivable that slightly different optical surfaces from the SKA1_mid dishes can be used for SKA1_survey, while sharing the mechanical structure and the local dish infrastructure (mount, foundation, control, etc.). Significant investigative effort is still needed to determine whether PAFs can be combined efficiently with offset Gregorian dishes. [5, Sect. 9.2] For SKA1 it is assumed that between 3 and 5 feeds are available and can be fitted for each antenna. [5, Sect. 8.3] The selected antennas are 15 m projected diameter, offset Gregorian optics. [5, Sect. 7] Designed for very high A e /T sys per unit of currency. The following are important qualitative characteristics required for SKA1 antennas [5, Sect. 7]: Excellent pointing. Excellent stability of key parameters (beam shape, pointing, etc.). Smoothness of response in spatial and spectral dimensions, as limited by fundamental physics (e.g. edge diffraction). Scattering objects tend to generate low level resonances, which will have relatively fine frequency structure and/or chromatic sidelobes. Space at the focus for five independent receivers. Thursday, 06 June 2013 Page 11 of 48

12 Very low sidelobes beyond the first one. Excellent polarisation performance. Circular beam. Excellent performance down to ~450 MHz, good performance to 350 MHz. Excellent performance to 15 GHz, good performance to 20 GHz. Equivalent physical aperture 15 m diameter Low Frequency 350 MHz High Frequency 20 GHz Optics Clear aperture 1st sidelobe 21 db Far out sidelobe level < 50 db Polarization purity 30 db Within HPBW Beam symmetry TBD Receivers 5 Cryo cooled, spanning frequency range Elevation limit <15 deg Azimuth range ±270 deg Pointing repeatability 10, 17,180 arcsec P, S, D respectively arcsec, rms Receiver noise temperature & Feed Losses <15 K Assumed for performance estimates Classes of Environmental Operating Precision Wind <7 m/s; night Conditions Standard Wind <7 m/s; day Degraded Wind <20 m/s Operation continuous Except for extreme weather. Table 2 Summary of the most important Dish Performance Requirements Extracted from [5, Sect. 7, Table 5]. SKADC Technical Solution The following were agreed as appropriate baseline SKADC Technical Solution: 2 axis (az el) no 3 rd axis Mount etc; steel; El range deg; Az range +/ 270 deg [5, Sect. 7] Wind survival 45 m/s (~160 km/hr); normal full spec operations 8 m/s (~30 km/hr). Slew speeds 2 deg/s (Az), 1 deg/s (El) Design lifetime 50 years Thursday, 06 June 2013 Page 12 of 48

13 2.4 SINGLE PIXEL FEEDS SKA_mid RfP Baseline Band #. Band (GHz) RF BW IF BW (GHz) Band :1 1 Antenna & Feed Efficiency 400 MHz 0.78 above 600 MHz Band : Band : Band : Band : GHz 0.7 above 8 GHz Table 3 Summary of the most important SKA1 Mid Array requirements Extracted from [5, Sect. 7, Table 6]. Polarisation: Dual (2 orthogonal) [5, Sect ] Only the two lower frequency feeds need be populated for SKA1 science [5, Sect. 8.3] Efficiency At the lowest frequency it is important to provide a relatively compact feed (although it will still be larger than any other feed). At the frequencies below ~400 MHz, the optics design will limit the efficiency and spillover noise, even with a large feed. For example, with a small sacrifice in efficiency, a quad ridge feed design is both fairly compact and has the potential for wide bandwidth. A 3:1 feed design has been selected here. Other feed designs, such as an Eleven feed [15] may also be suitable. [5, Sect. 8.3] Optimize for A e /T sys ; 1st sidelobe: 21 db; Far out sidelobe level < 50 db [5, Sect. 7] Excellent performance down to ~450 MHz, good performance to 350 MHz. [5, Sect. 7] Feed system flexibility: Once the dish designs are fixed, the main avenue for improvement of the system is by replacing feeds and receivers with better models. A critical design requirement for SKA1 dishes is the capability to allow this to be done with as little interference with other parts of the system, especially other feed bands. [5, Sect. 8.3] Cryogenic cooling An initial cryogenics study was carried out in 2012 to examine options and to develop a cost model for the SKA [16]. The main conclusion of this study is for a given requirement for A e /T sys performance, that cooling of receivers to physical temperatures between 20 and 100 K is cost effective by a large factor. The optimum temperature depends on the contributions of operations costs (electricity and maintenance), dish capital cost, and the fraction of total system cost attributable to the dishes. Various forms of Stirling and more traditional Gifford McMahon coolers were evaluated. As would be expected, the higher the system cost per dish, the more cost effective cryo cooled receivers become. Or for a given A e /T sys, fewer dishes are needed when the receivers are cooled. [5, Sect. 7.1] Only one receiver can operate on any antenna at one time. [5, Sect ] Thursday, 06 June 2013 Page 13 of 48

14 SKADC Technical Solution The following were agreed as appropriate baseline SKADC Technical Solution: SKA 1 shall be outfitted with Bands 1 2; [5, Sect. 8.3] The design phase will consider all 5 bands as this may have an impact on the dish selection. The higher frequency feed package will be developed to the same level as bands 1 and 2, but may not be rolled out in the initial stages. Optimise design for good performance in the MHz band; dish efficiency should be very good for observing frequencies above 600MHz It should be pointed out here that the efficiency specified in the RfP baseline requires shaped optics especially at the lower bands where physical size constraints limit the possibility of shaping feed patterns. Even with shaping, diffraction may limit the actual performance at 600 MHz. It is proposed to achieve the required sensitivity by reducing the system temperature as much as possible. All 5 single pixel feeds shall be accommodated on the one feed indexer. All feeds shall be located at the secondary focus; The SKADC Technical Solution specifically excludes the option of feeds being swung into the primary focal region of the primary reflector. The SKA_mid dish will receive in two linear polarisations. All orthomode transducers (OMTs), apart from Band 1, shall be cooled The Band 1 feed aperture would most likely be too large to put the entire feed inside a vacuum vessel and the feed design may make it impossible to have a thermal break inside the feed. It is thus likely that only the LNAs will be cooled. For Band 2 the lossy parts of the OMT will be cooled to between 50 K and 70 K in a cryostat whose outer wall is also the vacuum boundary. All LNAs shall be cooled to < 20 Kelvin; A cost/benefit analysis has shown that cryogenically cooling the LNAs is cost effective. The proposed baseline design requires cooling all LNAs to < 20 K. The detailed cooling study may suggest cooling some LNAs to 30 K. There will be three (3) integrated cryostats; Baseline design: There will be three dewars that will accommodate Band 1, Band 2 and Bands 3, 4 & 5 respectively. It is impractical to combine the lower frequency bands into a single cryostat as the space between feeds would lead to a very large cryostat, unless all feeds are mounted as spokes protruding outward from a central cryostat. This would severely restrict the length (and the possibility of future change) of all the feeds. The cryostats will share a single helium compressor with provision for reduced output during the roll out phase when not all feeds are installed. Each dish will be fitted with an automated vacuum system to simplify installation (e.g. after servicing the cryostat) and allow vacuum regeneration if a cryostat has been installed long enough for cryo pumping to become ineffective. The individual single pixel feed package will have as little control as possible and will communicate via slow serial optical fibre links with a central Feeds Controller in the Antenna Pedestal. This controller will also control the helium and vacuum services. Thursday, 06 June 2013 Page 14 of 48

15 Gifford McMahon cryogenic coolers; The SKADC Technical Solution specifies Gifford McMahon cryogenic coolers [5, Sect. 7.1]. There are alternative technologies which may be applicable which promise a reduction in both procurement and operating costs with increased reliability, e.g. Sterling Cycle coolers. However these technologies do not have the same level of maturity as current Gifford McMahon systems. Furthermore, experience thus far is that currently fielded systems have only been able to demonstrate an improvement in one of these areas. As such, Gifford McMahon coolers offer the only viable solution on the SKA1 timescale. The improvements promised by these alternative technologies are significant and therefore work should be carried out to develop them to the level of maturity necessary for their inclusion in SKA2. If the promised improvements were demonstrated on a suitable timescale for inclusion in SKA1 then this would be contemplated. However this work will not form part of the critical path for SKA1 feed package development. Dewar will be designed to survive at least 3 minutes without power and then restart without requiring maintenance Band 1 Feed Package The proposal for the Band 1 feed package is to consider both the Eleven Feed and the Quad Ridge Feed Horn (QRFH) and evaluate their performance at the same time as the optical down select. In both cases, only the LNAs will be cryogenically cooled. This results in a small cryostat that needs to be very close to the feed output. Figure 1 CAD model of Eleven Feed for GHz band. Thursday, 06 June 2013 Page 15 of 48

16 The proposed Band 1 LNA design is based on the technology developed for the ALMA Band 3 IF cryogenic LNAs. After prototyping at NRC Herzberg, these were manufactured in large volume (350) by Nanowave Inc. in Canada. The design uses discreet InP transistors and allows optimum performance while cooled at 15 K. Noise of the 4 8 GHz ALMA LNAs is below 4 K. Following on this design NRC Herzberg prototyped and manufactured LNAs for the MeerKAT L Band, MHz. Noise of the LNA, when cooled at 15 K, is 3 K. To date, 8 units have been delivered to EMSS, for the pre production phase. NRC Herzberg is currently prototyping a Band 1 SKA LNA using the same technology, with similar expected performance Band 2 Feed Package The Band 2 feed package will be a scaled (factor 900/950) version of the MeerKAT L Band feed (shown in Figure 2) that is currently at TR level 7. It will consist of an axially corrugated horn optimised to give a flat pattern with sharper drop off at the edge angle than a typical Gaussian beam. The feed horn will be optimised for an optimum A e /T sys over the band, probably resulting in a spill over of around 4 to 5 K. This is connected to a compact OMT constructed with dipoles in the back of the waveguide which also form the cryostat wall. The LNAs will use 3 stages with InP HEMT transistors similar to the MeerKAT ones. Additional RF gain on a temperature stabilised platform inside the cryostat will allow conditioning the RF output for a simple interface to the Receiver. The LNAs will be cooled to 15 K and the OMT to between 50 and 70 K. This should result in a receiver noise temperature of below 10 K and a total system temperature about 20 K. Figure 2 MeerKAT L Band Receiver (left) with cryogenic waveguide load for noise calibration Band 3, 4 and 5 Feed Package The Band 3 feed and OMT will be a scaled version of the Band 2 feed Band 3 receiver LNA MMIC The low noise amplifier MMIC will be designed and fabricated by Fraunhofer IAF. For a joint project (IAF, MPIfR, IRAM) aimed to exploit the potential of Fraunhofer IAF s metamorphic high electron mobility transistor (mhemt) technology for cryogenic applications several demonstrator MMIC LNAs were designed, one of them a 3 stage LNA in the frequency range 1 4GHz employing external input matching of the first stage. The HEMT technology used at that time featured gate lengths of 100 nm, achieving f T of more than 220 GHz. Fig. 1 shows the MMIC used in a demonstrator LNA built and characterized in 2009 by MPIfR. Thursday, 06 June 2013 Page 16 of 48

17 Figure GHz LNA MMIC and assembled demonstrator module. Performance of this initial design is very promising. Fig. 2 shows measured performance at ambient and cryogenic temperatures. Noise temperature in the band of interest here was ~6K for a physical temperature of 18K of the module. Figure 4 Measured gain and noise temperature of the demonstrator module at a physical temperature of the module of 300K (left) and 18K (right), frequency range 1 4GHz. By reducing the gate lengths to 50 nm even higher transit frequencies (f T ) of more than 375 GHz and consequently even lower noise figures and higher gain are achieved by Fraunhofer IAF. Since Fraunhofer IAFs 50 nm mhemt technology offers best cryogenic noise performance and has been validated at cryogenic temperatures in several national and international projects in close cooperation with the MPIfR, any MMICs developed for Band 3 of SKADC will be fabricated in this well established 50 nm mhemt technology, thus combining a cryogenic noise performance competitive to the InP process with the big technological advantage of fabrication on cheaper, less brittle GaAs substrates which makes the mhemt process an ideal candidate for large scale production for the SKA. Based on the demonstrated results and the improvements guaranteed by the advanced technology together with the reduced requirements on bandwidth, the main design goals and challenges are to deliver a noise performance of less than 5 K average noise temperature and to increase the gain above 30 db while not jeopardizing the input return loss (IRL) requirements of 15 db on module level. Thursday, 06 June 2013 Page 17 of 48

18 Band 3 receiver LNA module Module will employ a LNA MMIC fabricated using Fraunhofer IAF s 50nm cryogenic mhemt process. Baseline chip is a redesign of an existing 1 4GHz LNA MMIC. Due to the low frequency of the band, and since use of a cryogenic isolator on the input of the LNA has to be avoided, an additional input matching circuit external to the MMIC might be necessary to simultaneously meet noise and IRL specifications. RF input and output of the LNA module will have DC blocks and will therefore not carry DC voltages. RF input and output connections of the module will be standard SMA connectors. Mechanical interface specifications must be provided by OMTpackage subtask. Interface specifications for DC bias connector and for mechanical attachment including cryogenic interface will be provided by the cryostat package subtask. The LNA module will provide basic lowpass filters for DC bias connections to protect the chip from harmful ESD. Further RFI filtering may be necessary and this will need to be determined as part of pre construction. Frequency range GHz Gain 30dB Noise temperature 6K Input return loss 15dB Output return loss 10dB DC power dissipation 40mW Operating temperature range K, all specifications T amb =15K No. of voltages for DC bias 4 Reference impedance 50Ω Test & verification of specs As outlined in the work plan Table 4 Summary of specifications for the LNA module for the Band 3 receiver. The band 4 feed may use a more conventional quad ridge OMT as the dimensions of the dipoles and the coaxial feed lines extending from the back short become more critical at higher frequency Band 4 The feed will be a corrugated horn that will cover GHz. The feed will be optimised for A e /T sys on the final selected optics (in addition to the feed optimisations during the optics down select process). The entire feed and OMT would be cooled for best sensitivity Band 5 The feed will be a corrugated horn or quad ridge horn that will cover GHz. The feed will be optimised for A e /T sys on the final selected optics (in addition to the feed optimisations during the optics down select process). The entire feed and OMT would be cooled for best sensitivity. 2.5 FEED PACKAGE SKA1_survey RfP Baseline It is assumed that the dishes can easily accommodate three PAFs for different frequency ranges, but only one would be populated for SKA1 [5, Sect. 9.1] Only one feed available at a time [5, Sect ] Upgrade Path: It is not anticipated that SKA1_survey will be expanded to SKA2. SKA1_survey could be enhanced by the addition of more PAF arrays to cover a greater frequency range. In principle, these could be added Thursday, 06 June 2013 Page 18 of 48

19 in such a way as to share the beamformers. [5, Sect. 9.1] Band #. Band (GHz) RF BW IF BW (MHz) PAF diameter (m) Average T sys (K) Band : Band : Band : Table 5 Summary of the most important SKA1_Survey Array requirements Extracted from [5, Sect , Table 15]. Polarisation: Dual (2 orthogonal) [5, Sect ] Number of PAF elements: 188 (94 each polarisation) [5, Sect ] Number of PAF beams: 36 [5, Sect ] SKADC Technical Solution The following were agreed as appropriate baseline SKADC Technical Solution: Phased array feeds may be located at the primary focus (where there is no secondary reflector) or at the secondary focus. This baseline SKADC Technical Solution includes designs where: the PAF is located at the secondary focus of the Gregorian optics, or the PAF is located at the focus of the primary reflector, there being no secondary reflector in this case. The baseline SKADC Technical Solution specifically excludes the option of dual reflector optics with PAF(s) being swung into the focal region of the primary reflector. PAF sized to accommodate 6x6 beams at band centre [5, Sect ] Each PAF will have ~200 RF receiver elements that are digitised before being combined in a beamformer to form 36 dual polarised beams (72 outputs in total). All 3 phased array feeds shall be accommodated on the one feed indexer Band 1 will be a chequerboard based design because it is believed that a Vivaldi array would be too large. Band 2 could be either Vivaldi or chequerboard feed type. Both feed types to be tested/compared on like forlike basis (testbed) before PDR to allow evaluation in time for Dishes PDR. The CSIRO ASKAP phased array feed would be option zero if the chequerboard feed type is chosen; the value of reworking this design to exact SKA specification is minimal. Thursday, 06 June 2013 Page 19 of 48

20 2.6 RECEIVER PACKAGE SKA_mid RfP Baseline Band #. Band (GHz) RF BW (MHz) IF BW (GHz) # of Ifs # of bits Data Rate Gb/s 1* * * Bands 1 and 2 are a priority for SKA1 [5, Sect ] Table 6 Summary of the most important SKA1_Mid Array requirements Extracted from [5, Sect. 7, Table 6]. Only one receiver can operate on any antenna at one time Only one receiver can operate on any antenna at one time. Some receiver bands may be divided into sub bands, only one of which may overlap a MeerKAT band. In that case the other band can be correlated as one or more sub arrays of SKA1 antennas, [5, Sect ]. At least bands 1 and 2 will be available for SKA1 To cover the key SKA1 science, only the two lower frequency feeds need be populated [5, Sect. 8.3]. At least SKA1 bands 1 and 2 will be available. Depending on funds, not all of the other SKA1 receivers will be initially available. It is assumed that the correlator, non imaging processor and similar equipment will be sized to fit the maximum requirements, or will be specifically designed to be expandable to such [5, Sect ]. Digitise the RF band at the antenna Signals from the dishes will be transported to a central signal processing building via the digital data backhaul system. The SKA1_mid array will transmit data from the output of the digitising stage at the receiver to the input of the signal processing system. The transmission will use optical fibre to carry digitised data. It will be a point to point deterministic network in which the data flows in a unidirectional fashion from the antennas to the central processor for SKA1_mid. [5, Sect. 8.5] Synchronisation will be provided at each antenna The synchronisation sub system within the SKA to provide the frequency reference signals required. Coherence can be maintained through the use of accurate independent clocks or by a frequency reference distribution from a central reference clock. At every antenna or station, the synchronisation system will provide a standard reference sine wave from which clocks for digitisation and/or local oscillator signals can be derived and a pulse per second (1 PPS) signal from which time tags can be derived [5, Sect. 11.0]. Timing signals will be provided at each antenna Sufficiently accurate Coordinated Universal Time (UTC), converted to sidereal time using regularly published Earth rotation data (UT1 UTC and higher order corrections will be provided [5, Sect. 11.1]. MeerKAT will be incorporated into the joint array The key parts of the MeerKAT system will be incorporated into the joint array. This includes the receivers, synchronisation and time distribution, and data transport system [5, Sect ] Thursday, 06 June 2013 Page 20 of 48

21 In Band 5, two 2.5 GHz bands can be observed simultaneously [5, Table 6] SKADC Technical Solution The following were agreed as appropriate baseline SKADC Technical Solution: Only one receiver can operate on any antenna at one time [5, Sect ] At least bands 1 and 2 will be available for SKA1 [5, Sect ] The proposed implementation is shown in Figure 5. A common sampler is used for bands 1 4. Bands 1 4 and the low frequency part of Band 5, designated Band 5a would be directly sampled in the first or second Nyquist zones, as outlined in Table 7. The higher frequencies in Band 5, designated Band 5b Band 5d would be down converted with a high side local oscillator and the IF would be sampled in the first Nyquist zone, as outlined in Table 8. Band Frequency Range (GHz) No. of Ifs No. of bits Sample clock (Gs/S) Total (Gb/S) Comment 1* Direct Sample in 1st Nyquist Zone 2* Direct Sample in 1st Nyquist Zone Direct Sample in 1st Nyquist Zone Direct Sample in 1st Nyquist Zone 5a Direct Sample in 2nd Nyquist Zone * Bands 1 ad 2 are a priority for SKA1 [5, Sect ] but the receiver system for band 3 is also implemented as part of the technical solution. Table 7 SKA1 Receivers Technical Solution Bands 1 5a. Band Frequency Range (GHz) No. of Ifs No. of bits Sample clock (Gs/S) Total (Gb/S) LO Frequency (GHz) Sampled IF Band (GHz) 5b c d Table 8 SKA1 Receivers Technical Solution Bands 5b 5d. In Band 5, any two 2.5 GHz bands can be observed simultaneously [5, Table 6] Note that the sampler clock frequencies and the local oscillator frequencies are within Band 5. cause interference when two, 2.5 GHz bands, in Band 5 are observed simultaneously. These may Synchronisation will be provided at each antenna [15, Sect. 11.0]. Band 5 implementation will require a local oscillator (LO) derived from the reference signal at each antenna. Round trip phase measurement and tracking is likely to be required. Thursday, 06 June 2013 Page 21 of 48

22 Digitise the RF band at the antenna [15, Sect. 8.5] Timing signals will be provided at each antenna [15, Sect. 11.1] Components of the system will be located in both the antenna and at the central site The baseline design assumes digitisation at the antenna. This may occur at the focus or in the pedestal. Terminal equipment and/or digital signal processing hardware will also be required at the central site. The exact requirements and locations of the various sub system components will be implementation specific. Sampler clocks and other signals will be required. Both polarisations will be observed at the same frequency Figure 5 Block diagram of the SKA_mid receiver package. Thursday, 06 June 2013 Page 22 of 48

23 2.7 RECEIVER PACKAGE SKA1_survey RfP Baseline Band #. Band (GHz) RF BW IF BW (MHz) Band :1 500 Band :1 500 Band :1 500 Table 9 Summary of the most important SKA1_Survey Array requirements Extracted from [5, Sect , Table 15]. Polarisation: Dual (2 orthogonal) [5, Sect ] Number of elements per PAF : 188 (94 each polarisation) [5, Sect ] Average PAF efficiency (Band 2): 0.8 Area weighted average over beams and frequencies [5, Sect ] Maximum available bandwidth: 500 MHz [5, Sect ] Number of sample streams per PAF element: 2 x 8 bits (both pol ns) [5, Sect ] Number of PAF beams: 36 [5, Sect ] PAF signal/data transport The following two possibilities result in slightly different approaches to interfacing with PAFs and ASKAP equipment to the combined telescope system: [5, Sect ] 1. The ASKAP Mark III PAFs are likely to utilise RF over fibre to transport the RF in analogue form from each element of the PAF array to a processing centre, where digitisation takes place. In the case of ASKAP, the processing centre is the central correlator building. However, the maximum reach of RF over fibre is about 10 km. Thus if this model is adopted for more distant SKA1 antennas, then enclosures supplied with power will be needed at strategic points in the array configuration. Digital data would then be transported from these enclosures to the central building. Optionally, beamforming will also take place in these enclosures to reduce the amount of data transmitted. 2. If the Mark III PAFs are equipped with internal digitisers (or upgraded to such), then digital data will be transmitted all the way to the central correlator building. Optionally, beamforming will take place in or near the antennas to reduce the amount of data transmitted. RF over fibre (analog) to Digitiser location: 188 fibres; one switchable RF over fibre subsystem per antenna. [5, Sect ] Thursday, 06 June 2013 Page 23 of 48

24 SKADC Technical Solution The following were agreed as appropriate baseline SKADC Technical Solution: All SKA1_survey bands shall be sampled at full bandwidth. Whilst full bandwidth is the baseline, options for lower sample rates will also be investigated. Processed (IF) bandwidth = 500 MHz. [5, Sect ] The polyphase filterbank shall be sized to process SKA1_survey Band 2. SKA1_survey Bands 1 and 2 will require less processing power than SKA1_survey Band 3. Select 500 MHz of bandwidth to output from the polyphase filterbank to the beamformer. SKA1_survey Band 3 will have a higher processing requirement and the polyphase filterbank for Band 3 will be supplied when the SKA1_survey Band 3 receiver system is installed. The SKA1_survey receiver system will be split so that part will be located at the focus and the remainder will be located off the dish. On dish sampling and beamforming is the SKA baseline design. However, a first review of this option (as scoped, with ASICs) looks to be too large or heavy to be located at the focus. The analog (RF) portion of the receiver system will be split so that part will be located at the focus and the remainder will be located off the dish together with the sampler and beamformer. RF over fibre links will be used to send the RF signal to the off dish portion of the receiver system. Figure 6 Block diagram of the SKA1_survey receiver package. Thursday, 06 June 2013 Page 24 of 48

25 2.8 POWER The power requirements of the Dish systems will be significant. The major contributions to the Dishes power budget will be from: Antenna drives Cryogenics systems Electronics including the digital processing associated with the PAF systems Environmental cooling of the electronics systems. The power requirements will be estimated for the RfP response to set a baseline. 2.9 Local monitor and control Comprehensive monitor and control shall be designed to interface the Telescope Manager (TM) and the dishes (e.g. antenna drives, feed and receivers and other systems), to permit the scheduled observations and feedbacks to the TM. Interface Telescope Manager dish Interface TM and simulator Interface with Dish and simulator The Local monitor and control (LMC) system shall permit the dish operations, monitor the status, provide alarms and request for maintenance. Dish operation Pointing, tracking, receiver setup, sensors... Determination of pointing corrections Logging Alarms, safety, request for maintenance Figure 7 Outline of LMC system. Thursday, 06 June 2013 Page 25 of 48

26 2.9.1 LMC implementation Hardware Rack with computer, interface boards for interfaces, data archiving Size of the system about 50x50x50 cm Additional space for 2 computers (simulators) Software Operating System: Open source (Linux real time), Programming language: C/C++ (or python, Java) Other Need for power (~2 kw), cool air (operative temperature range C, probably OK inside the basement of the dish without air conditioner) Thursday, 06 June 2013 Page 26 of 48

27 3 Implementation Estimates SKA TEL.DSH.MGT CSIRO TS 004 The information in this section is to allow the commencement of e.g. Optics, Structure, etc, studies and to provide the Feed and Receiver design groups with upper bounds on the systems to design for PDR. 3.1 FEED PACKAGE SKA1_mid SKADC Technical Solution Estimates Assuming an effective f/d = 0.5, the feed suite to be accommodated Bands Feed Type Area on Feed Indexer (dia m) Volume Feed Package (m 3 ) Mass Feed Package (kg) Power (W) Cryogenic Systems Comment 1 (1)(2) Eleven kW (4,5) Cooled LNA 1 (1)(2) Quadridge kW (4) Cooled LNA 2 (1) OBSPF OBSPF OBSPF Horn m 3 (Length ~1m) 0.1 m 3 (Length ~1m) 0.1 m 3 (Length ~1m) 0.1 m 3 (Length ~0.5m) 60 2kW (4,5) OMT and Cooled LNA Cooled OMT and LNA 100 5kW (4) OMT and Cooled LNA Cooled OMT and LNA Feed Rotation required Feed Rotation Required Common Cyrostat (3) (1) Bands 1 and 2 are a priority for SKA1 [5, Sect ]. (2) Only one of these feed package types will be part of the final technical solution. (3) OMT and LNAs for Bands 3, 4 and 5 will be housed in a common cryostat. Feed horns will be external to the common cryostat. The final dimensions will depend on the feed indexer layout. (4) Estimate includes power consumption of compressor necessary for cryogenic cooling. (5) When sharing a compressor between multiple cryostats. Compressor availability may require that the compressor rating be slightly larger than the sum of the components. Table 10 SKADC Feed package Estimated requirements 3.2 SKA1_Survey SKADC Technical Solution Estimates The SKA1 Survey PAF system will be architecturally and physically separated into at least two major parts (or sub systems). A portion of the system will be located at the focus of the antenna. Assuming an effective f/d = 0.5, the feed suite to be accommodated Thursday, 06 June 2013 Page 27 of 48

28 3.2.1 SKADC Technical Solution Antenna Sub System(s) The estimated requirements of the antenna based sub system(s) of the SKA receiver system are detailed in Table 11. The estimate provided is for the implementation detailed in Section 2.6 and are indicative only. Bands PAF Beams Area on Feed Indexer (m 2 ) Package Depth (m) Mass at Focus (kg) Power (W) Support Systems Comment 1 36 (critically sampled at 0.9GHz) 3.0m dia 0.5 Dry Air 2 (1) 36 (critically sampled at 1.7GHz) 1.5m dia Dry Air 3 36 (critically sampled at ~4GHz) 0.7m dia Dry Air (1) Band 2 is a priority for SKA1. Table 11 SKADC PAF Feed package Estimated requirements 3.3 RECEIVER PACKAGE SKA1_mid SKADC Technical Solution Estimates The SKA receiver system will be architecturally and physically separated into at least two major parts (or subsystems). A portion of the system will be located as close as practicable to the feed system, i.e. at the focus of the antenna. Figure 8 Outline of SKA1_mid Feed/LNA and receiver system. The SKA dish array receiver system will have overlap with and will be influenced by: Signal Transport, and Timing and Synchronisation. Thursday, 06 June 2013 Page 28 of 48

29 3.3.1 SKADC Technical Solution Antenna Sub System(s) The estimated requirements of the antenna based sub system(s) of the SKA receiver system are detailed in Table 12. The estimate provided is for the implementation detailed in Section 2.6 and is indicative only. Band Frequency Range (GHz) 1 (1) (1) Volume (litres) 30 (0.3m x 0.3m x 0.2m) Mass (kg) Power (W) Mount Options 30 (3) 200 (3) Dish Focus Pedestal 4 (2) Same enclosure as Band (3) 50 (3) Focus Dish Pedestal 5a b c (0.3m x 0.3m x 0.2m) 30 (3) 150 (3) Focus Dish Pedestal 5d Support Systems Cooling Temp Control Dry Air Supply Same enclosure as Band 1 3 Cooling Temp Control Dry Air Supply Comment RFI Shielding required RFI Shielding required RFI Shielding required (1) Bands 1 and 2 are a priority for SKA1 [5, Sect ] but the receiver system for band 3 is also implemented as part of the technical solution. (2) Although these bands are not a priority the technical solution proposed is capable of supporting Band 3 and with Band 4. (3) Mass and power consumption are estimates only. They do not include elements of synchronisation and timing (e.g. clock generation, terminal equipment), reference distribution (e.g. LO cleanup loop or LO source), or power regulation (e.g. DC supplies and regulators). In some implementations these components may be integrated into the receiver package; if so, the receiver package will have an additional weight and power requirement. Table 12 SKADC Receiver antenna sub systems Estimated requirements Thursday, 06 June 2013 Page 29 of 48