Technical Development

Coherent Arrays for Astronomy and Remote Sensing
This project is in its final year of technical development funding.

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The initial Coherent Arrays technical development overview is here.

The following update is from March 2011:

The major tasks on this project over the last year have been:

  1. Outfitting a new laboratory for radio frequency and digital work
  2. Measurements and testing of Monolithic Microwave Integrated Circuits (MMICs)
  3. Testing and Development of Receiver Modules

New Laboratory
We have completely outfitted a new laboratory – the Cahill Radio Astronomy Laboratory (CRAL) for radio frequency work and for digital work and we have designed and built a cryo-probe test station (CPTS) for testing undiced MMIC wafers up to four inches in size. This fabrication has just been completed and we are now carrying out our first cryo-tests of the equipment. Within a few weeks we expect to be making measurements of the wafers themselves. In the words of John Carlstrom – this is a real “game changer”.

Caltech Cryoprobe Station

Program of MMICs Measurement and Testing
We have just recently begun our program of measurement and testing of Monolithic Microwave Integrated Circuits (MMICs). An excellent example is shown in below.

MMIC testing results for two MMICs – SN01 and SN04

This shows results for two MMICs – SN01 and SN04. SN04 has been tested at JPL and in the CRAL – the two blue plots show the excellent agreement between the JPL and CRAL measurements. This device has also been tested in the lab at the Owens Valley Radio Observatory (OVRO) – see the short blue curve. The OVRO results are 5K-10K higher than the JPL and CRAL results. We are investigating this discrepancy. The results shown for SN01 (red curves) are extremely encouraging with a noise temperature below 41 K from 77 GH to 116 GHz. In terms of bandwidth plus noise temperature, this is the best device that has been produced, but its gain is rather low for our needs. The hope on the present program is to produce devices with noise temperatures about a factor two below what we see here and with gain greater than 20 dB.

MMIC Module Understanding
We have been making rapid progress in understanding our MMIC modules. We have broken some QUIET 90 GHz modules up into three sections – i.e. we have split up the module – in such a way that we can, for the first time, test the radio frequency performance of the MMICs inside the module packaging. A major breakthrough a few weeks ago was the discovery that our MMICs, when placed in modules, are oscillating at 67 GHz. It is clear that a considerable signal at this frequency was travelling back to the
orthomode transducer and then being reflected back into the MMIC, thereby raising the noise temperature of the module, which was running at around 100K, i.e. about 50K higher than the individual MMICs. We are now working on redesign of the module packaging to eliminate the oscillation at 67 GHz.

For questions contact: Tony Readhead, Charles Lawrence or Michele Judd

 

Tony Readhead

Tony Readhead, the Barbara and Stanley Rawn, Jr., Professor of Astronomy, leads the KISS supported Caltech and external efforts of this work.

 

Charles Lawrence

Charles Lawrence, JPL Principal Scientist, Astrophysics Element, leads the JPL R&TD supported efforts of this work.