1. 6 May 2009Lynn Baker AWG Meeting LA1 TDP Antenna and Feed Plan Lynn Baker Antenna Working Group Meeting Los Angeles, CA May 6, 2009

2. 6 May 2009Lynn Baker AWG Meeting LA2 Challenge: Make Progress On Antenna / Feed Selection With Limited Resources and Time Primary metric is antenna performance, A/T, per unit cost. Other important specifications are sidelobe levels, polarization performance, field of view. Identify criteria which can guide choices absent complete system specifications and obtain sufficient information to make that choice. Make cost comparisons between options in a ratiometric sense without detailed absolute costing of individual cases.

3. 6 May 2009Lynn Baker AWG Meeting LA3 Example: Basic Choice of Antenna Geometry There are four basic choices obtained by multiplying single / dual reflector and symmetric / offset options. Bracket price spectrum with dual offset as the most expensive and single symmetric as the cheapest. Estimate cost ratio by comparing subsystems from each option. Major subsystems: primary reflector and mount/drives. Estimate performance in a similar manner, ratiometric on factors like noise temperature, aperture efficiency, sidelobes, etc. Make geometry selection based on these ratios of cost and performance factors remembering that higher A/T means fewer antennas. This type of decision making does not apply to all cases.

4. 6 May 2009Lynn Baker AWG Meeting LA4 Other Antenna Selection Drivers The overall scaling of processing cost. If high order in the number of antennas then processing cost would be reduced by smaller numbers of higher performance antennas. This would also encourage larger antennas. High dynamic range imaging is a major driver of several antenna specifications but the detailed requirements are not yet defined. Stringent pointing stability / accuracy could be significant cost driver of structure and mount, pushes toward maximum performance reflectors. Satellite RFI is a potential significant driver of low sidelobe specifications. Study and tabulation of satellite signals is needed. The noise temperature performance of feeds and LNA’s weights the effectiveness of low noise antenna geometries.

5. 6 May 2009Lynn Baker AWG Meeting LA5 One Feed or Multiple Feeds? One feed avoids any form of feed changing mechanism but a single feed may have performance limitations. A changer mechanism is a relatively fixed cost for different numbers of feeds, 2 or 3. Note that the inclusion of a phased array feed will require a feed exchange mechanism since a PAF will only cover roughly an octave. Multiple feeds might have superior performance if limited to 4:1 / 3:1 bandwidths. Be ambitious, 1/T or 1/T^2 has a powerful affect on the number of antennas. Compare performance of ultra-wideband feeds to more common feeds with smaller bandwidth. Estimate cost of changer mechanism plus extra receiver packages.

6. 6 May 2009Lynn Baker AWG Meeting LA6 Feed / LNA Selection The illumination pattern from a particular feed will significantly affect the optical geometry of the matching reflectors. Reflector optics will be designed to match each feed and the result analyzed and selected as a package. Detailed, uniformly accurate feed data will be required for final antenna analysis. Obtaining this data can be done commercially, Satimo in Atlanta being one possibility. Establishing an antenna measurement range at Cornell is still a possibility but requires scarce staff resources. Various local options for feed testing are more convenient during feed R&D. The ATA has plans to use one of their antennas without a subreflector to obtain feed pattern data.

7. 6 May 2009Lynn Baker AWG Meeting LA7 TDP Prototype Antenna Caveats: Not constructed with advanced fabrication techniques being studied, hydroforming and composites. Can’t afford molds and tooling. Price of prototype will not be representative of SKA procurement costs. Estimate of two years to specify, design, bid, fabricate and install after internal selection of options is complete. Will consume considerable effort from AWG engineering pool.

8. 6 May 2009Lynn Baker AWG Meeting LA8 TDP Prototype Antenna Define Purpose Probably not necessary to build a prototype to demonstrate typical, mainstream performance. Modeling, simulation and experience can define the performance of such an antenna. Prototype should demonstrate performance and features that are unique and challenging. Verification plan should define exactly what should be demonstrated by the prototype and how that will be accomplished with a single prototype. Construction of a prototype should provide a large boost in confidence and credibility. The prototype will have performance representative of an SKA antenna if properly specified, designed and built.

9. 6 May 2009Lynn Baker AWG Meeting LA9 TDP R&D Continues Down selection to a prototype antenna should not stop continued development of all TDP research topics for the entire period of the TDP. The TDP should provide more antenna options to the SKA costed system design than just the prototype. Use of of TDP engineering talent represents a large implicit cost of the prototype antenna, lost opportunity to do further research.