• Project 543: Band 3 IF Bandwidth Upgrade Study

  • *Reviewer* 1

Grade: 3.5

Title: Band 3 IF Bandwidth Upgrade Study (strategic)

The goal is to investigate the feasibility of updating the bandwidth of Band 3 to move from the current 4-8 GHz output to a 4-12 GHz output, doubling the bandwidth.

1. Alignment with NA ALMA Partnership strategic goals;

Comment.

Good alignment with the increased bandwidth strategic goal.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

Comment.

The proposal very clearly spells out the scientific strengths of the doubling of band 3: - reduced integration times, greater depth and increased mapping speed. - reducing the number of LO tunings needs for wideband work. - more simultaneous spectral lines possible

3. Quality of the upgrade conceptual design; Comment:

The proposal does a very nice job of laying out a set of 4 approaches to the upgrade. Each is briefly described in terms of both effort and potential drawbacks. Overall this is a refreshingly clear description of issues to consider and well referenced. In this program they look in detail at the first two of the approaches for feasibility. This will be valuable to identify the need for options 3 or 4 which are more complex.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

Comment

The team is well poised to undertake the program study of increasing the Band 3 bandwidth to help identify the best upgrade strategy and issues impacting various Band 3 upgrade options.

5. Strength of the consortium organization (if applicable);

Comment.

6. Qualifications of the key personnel of the Study;

Comment.

The personnel involved in the program are well qualified based on past experience with with a wide range of radio instrumentation including ALMA Bands 1 and Band 3 work. They appear very well suited to undertake the proposed study.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Comment.

The facilities and technical experience of the team is excellent. The NRC Herzberg LNA group developed the LNAs for the current Band 3 and are well experienced in this work. The group also has the needed and relevant modeling experience.

8. Assessment of the level of risk inherent in the design;

Comment.

The level of risk inherent in the project is moderate but contingency plans are provided for the major risks identified.

9. Strength of the Scientific Team supporting the Study;

Comment.

10. Level of support guaranteed by the Institutes;

Comment.

NRC is providing in-kind contributions of facilities and material costs, 25% of the labor costs, they also cover the contingency costs associated with the estimated technical risks.

  • *Reviewer* 2
Review of proposal " Band 3 IF Bandwidth Upgrade Study" Proposal index number: 543

Principal Investigator: Lewis B. G. Knee

Cost: $356,383

In-kind contributions: $195,583

Review date: 9 July 2017

Overall score: 8.5 (0.1 best to 9.9 worst)

Proposal Summary It is proposed to investigate expanding the IF bandwidth of the Band 3 front end from 4 GHz (as 4-8 GHz) to 8 GHz (as 4-12 GHz). There are three parts to the study: (1) Simulate the performance of the current SIS mixers over the wider IF range, and perform direct measurements of the IF port impedance over that range. (2) Develop, fabricate, and test new 4–12 GHz cryogenic LNAs. (3) Test the mixers with the new amplifiers. The present Band 3 front end uses 2-sideband mixers, implemented with an IF hybrid before the IF amplifiers. Each amplifier is also preceded an isolator. In order to extend this architecture to the larger IF range, wider-bandwidth hybrids and isolators are also needed, but development of these is not included in the study. Apparently the investigators intend to procure commercial isolators, but there is some uncertainty about whether suitable ones will be available. The tests of part (3) will be done "both without an isolator and with a new 4–12 GHz cryogenic isolator (possibly available from Pamtech/Quinstar), but there are concerns about loss in that isolator" (page 6). The tests will be done without the hybrid, producing a DSB mixer and avoiding the need for a well-matched pair of SIS mixers. On the other hand, "[I]f we succeed in procuring a suitable 4–12 GHz hybrid, we will also attempt to investigate the 2SB performance" (page 6). No hardware or software will be delivered. NRC will provide substantial in-kind contributions, including 25% of labor costs, all materials and services, and all contingency, making the project's total value 552k$, of which 356k$ is the cost to the ALMA Development Fund.

Strengths and Weaknesses The investigators are well qualified to carry out the proposed work since some of them were involved in developing the present Band 3 cold cartridge. They have access to the test facilities built for that work (Mixer Test Set) and they have on hand spare SIS mixer chips and complete mixer blocks. They have an excellent LNA development group. There is a strong science case for increased sensitivity, and increasing the IF bandwidths of the front ends is part of that. It is closely aligned with goals of the ALMA 2030 Roadmap. However, this reviewer questions whether the specific program outlined in the proposal is useful to ALMA. The heart of the proposal is the development of new 4-12 GHz LNAs. They seem to have in mind packaged, single-ended, 50 ohm amplifiers like those of the current Band 3 front end. Yet such devices are readily available on the market; for example, both Low Noise Factory and Cosmic Microwave Technology have amplifiers with noise temperature < 5K over this frequency range when operated at 15K. No performance goals for the new amplifiers are given in the proposal. The proposal does not say what transistors would be used for the new amplifiers; presumably they will use transistor chips that the group has on hand, since no new chip development is mentioned. Under these circumstances, development of new LNAs for this application is hard to justify, and it is certainly not justified by information in the proposal. ALMA development funds could be better spent. To obtain funding, the proposers should make a convincing case that they can develop amplifiers that are significantly better than those already available; they have not done that. Other study proposals in this cycle also address IF amplifier development, but in more innovative ways that might lead to larger returns by not only increasing the accessible bandwidth but also reducing the receiver noise temperature. These include the development of balanced amplifiers (#529) and TKIP amplifiers (#536). Other tasks in the proposal are more useful. Simulation and IF impedance measurement of the existing mixers is worthwhile in order to understand how far that design can be pushed, but that task seems to account for less than 20% of the proposed effort. Testing of the existing mixers with wider-bandwidth IF amplifiers is also useful, but again it is a relatively small effort. What might be of immediate value to ALMA would be the construction of a complete prototype 2SB mixer assembly with 4-12 GHz IF outputs, but that is not proposed here because of the lack of suitable IF hybrids and isolators. There is considerable risk that the proposed test will not be successful or will produce poor performance because of mismatch between the mixer and amplifier. (Strangely, the testing effort accounts for more than 40% of the proposed cost.)

Scoring The main thrust of the proposed work is to design, fabricate, and test new 4-12 GHz cryogenic low-noise amplifiers. Yet no performance goals for these amplifiers are given, and important details such as the transistors to be used are omitted. The authors provide no reason for us to believe that the new amplifiers will be better than those that are readily available for purchase now. Neither the new amplifiers nor any other hardware would be delivered to ALMA. Other, more useful work is also proposed, but even if it is successful it would not move ALMA much closer to having a wider-bandwidth receiver in Band 3. For these reasons I am forced to give this proposal a poor score of 8.5.

  • *Reviewer* 4
Grade: 3.5

Title:Band 3 IF Bandwidth Upgrade Study

1. Alignment with NA ALMA Partnership strategic goals;

Proposal is well aligned with ALMA strategic goals.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

Proposal is to study the feasibility of doubling the bandwidth from 4 to 8 GHz for the ALMA band 3 receivers. Increased bandwidth for higher sensitivity and greater spectral coverage for line surveys, is a totally well justified scientific goal for all bands, including band-3.

3. Quality of the upgrade conceptual design;

All the goals of the proposed study are very appropriate to pursue: investigating the suitability of current SIS mixers, development of suitable Low Noise Amplifiers, IF hybrid, and matching of mixers to LNAs. Proposed study’s scope is restricted to receiver development and does not discuss other changes needed downstream- but a brief discussion on these, would not have been out of place.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

The existing band 3 SIS mixer chip was already designed to cover 4-12 GHz bandwidth but its performance above 8 GHz needs to be measured. Redesign of the mixer with new LNA is a longer term project, will have to be in collaboration with NRAO and University of Virginia.

5. Strength of the consortium organization (if applicable);

Very strong consortium. The team was originally involved in band 3 receivers development.

6. Qualifications of the key personnel of the Study;

Extremely well qualified team.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Team has adequate preparedness and experience and facilities at NRC for this development are well established.

8. Assessment of the level of risk inherent in the design;

Risk assessment is well discussed in the proposal, mainly on delay in LNA availability or other problems in deviation from expected performance.

9. Strength of the Scientific Team supporting the Study;

Very strong team.

10. Level of support guaranteed by the Institutes;

Full support guaranteed.

11. Budgeted cost of the Study;

$551,966 over two years. Budget seems well justified.

  • *Reviewer* 5

Grade: 8

Band 3 IF Bandwidth Upgrade Study

1. Alignment with NA ALMA Partnership strategic goals:

This proposal is well aligned with the strategic goal of increasing the IF bandwidth of the ALMA receivers.

2. Strength of the scientific case for the proposed ALMA upgrade concept: Comment on the relevance to the ALMA 2030 development documents.

Excellent. Doubling the IF bandwidth is clearly shown to help multiple science cases, from reducing integration time in continuum mode to reducing observation time of the entire band.

3. Quality of the upgrade conceptual design:

Evaluating the least intrusive approach is the prudent lowest-cost path to increasing the bandwidth of the band. While the SIS mixer may eventually need to be redesigned for more IF bandwidth or better matching to the LNA, testing of the existing infrastructure should be conducted first.

The proposed approach will attempt to design a better matched IF amplifier that does not require the isolators, similar to those mentioned in Ref [8].

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development):

Unclear. This study will reveal if a less intrusive approach of increasing the IF bandwidth of Band 3 is feasible, or if more extensive redesign is required.

5. Strength of the consortium organization (if applicable);

N/A

6. Qualifications of the key personnel of the Study;

Excellent.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Excellent. As part of the Band 3 development team, the investigators and institute are appropriate for this study.

8. Assessment of the level of risk inherent in the design;

Moderate. The project relies on the existing SIS mixer to operate from 4-12GHz. Although these devices were designed for this band they have never been measured.

9. Strength of the Scientific Team supporting the Study;

N/A

10. Level of support guaranteed by the Institutes;

Excellent. 25% of the labor cost will be covered by NRC

11. Budgeted cost of the Study:

The cost seems reasonable for the amount of testing and the LNA development effort.

  • *Reviewer* 7

Title of ALMADev Proposal: "Band 3 Bandwidth Upgrade Study" By Knee et al.

Review Comments

The proposers will investigate and develop methods to increase the IF bandwidth of the current Band 3 receivers from the current 4-8 GHz to 4-12 GHz. They will check the suitability of current SIS mixers for the wider bandwdith, develop new IF LNAs with broader bandwidths, examine IF hybrids, and also look into better matching networks between the mixer and IF amplifiers.

The science case for the proposal is strong. Doubling the IF bandwidth of Band 3 mixers is very desirable to get better continuum sensitivity and faster coverage of the 3mm band for line surveys.

However, there are several significant weaknesses in the proposal. While a development of IF LNAs is proposed no details are presented whatsoever about the technology, any past history of development, prospects for such devices, etc. The truth is low-noise amplifier development at these frequencies is very mature now, with CDL having developed acceptable amplifiers and at least one commercial company (Low Noise Factory) that produces state of the art very low-noise cryogenic IF LNAs. So if there is new development to be done, the need for this new development is not justified, nor are the techniques to be used presented.

IF quadrature hybrids are also commercially available readily for this bandwidth (MAC Technology), so this is not a research effort to find such hybrids. Matching circuits to best match SIS mixers to IF amplifiers are also a known and solved problem for most low frequency SIS devices (see the work by Kerr et al.).

Another problem in the proposal is the investigation of broad-band isolators. Having established that isolators can be lossy and sacrifice precious noise temperature performance, it is not clear why broadband isolators (which too are commercially available) needs any study.

In summary much of the proposal does not cover new topics of study, and can be done for a much lower price tag.

Review Score: 9.8

  • *Reviewer* 10

543 Band 3 IF Bandwidth Upgrade Study Lewis Knee

Score: 8

The authors propose to upgrade the band 3 IF bandwidth to cover 4-12 GHz. The key goals would be to develop a new broadband amplifier (4-12 GHz) to replace the existing (4-8GHz) amplifiers and also to study if a new 4-12 GHz isolator is required, or if the new amplifiers can be directly interfaced with the SIS mixers. If the latter is not feasible, the approach will be to procure new broadband isolators.

While upgrading the operating bandwidth of the ALMA band 3 system would be highly beneficial to the overall instrument performance, the justification for designing a new amplifier was not made clear. Furthermore, sufficient details into the technology used to implement this amplifier as well as the amplifier configuration were not provided, making it difficult to evaluate the potential for reaching the levels of noise performance that have already been achieved using state of the art InP HEMTs. In other words, simply stating that the amplifier will be made using ‘chip and wire’ techniques does not permit evaluation of the potential for success. Unless the proposer has access to a technology such as Chalmers or NGST, it is unlikely that they will achieve the levels of performance already achieved by commercial amplifiers. Of course, if they could make the argument that their amplifier would be designed with sufficient return loss to permit removing the isolator, then that might justify some extra noise in the amplifiers. However, the authors would still need to explicitly state why this could not be done using existing solutions (e.g., the LNF-LNC4_16B, which has greater than 10dB return loss and ~4K noise).

  • *Reviewer* 12

Proposal 543:

- Comment: This proposal aims to upgrade the Band 3 system.

- Score: 3

-- AlWootten - 2017-07-18
Topic revision: r2 - 2017-07-18, AlWootten
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