Overview of High-Power and Wideband Radar Technology Development at MIT Lincoln Laboratory

Round 1

Reviewer 1 Report

Really enjoyed reading this well prepared and highly readable paper. Interesting development of the ionising hybrid switch.

Author Response

Thank you for your review.  The ionizing switch is indeed an interesting item.

Reviewer 2 Report

After a thorough review of your article, I find that it aligns more closely with the style and content of a popular science magazine than a traditional academic journal. Work is undeniably interesting and broadens horizons, delving into historical aspects of the field. However, it primarily reorganizes and elucidates a small, historical segment of the discipline rather than contributing new insights or advancements. While the historical perspective is valuable, its application in advancing the field is limited. I recommend considering submission to a publication that caters to a broader, more general audience interested in the historical context of scientific topics.

Author Response

Thank you for your review.  I agree with your assessment that this is a historical review rather than a paper containing new research.  We were invited to prepare a review of our radar activities by the editor and responded to the spirit of his request.

Reviewer 3 Report

The authors provide a refreshingly well-written, well-organized, and comprehensiv overview of radar technology development at MIT Lincoln Laboratory. The paper is a very good read and gives the reader a nice chronological overview with plentiful references.

I only have a few minor suggestions to the authors:

Figure 1:
The quality of Figure 1 is quite poor compared to the rest of the paper. It seems that the figure is a screenshot from a document. This should be improved.

Line 176:
There seems to be a comma missing after "... technology [20] ...".

Page 7, footnote 1:
There seems to be a comma missing after "... in 2014 ...".

Line 227:
There seems to be in apostrophe missing in "... radars history ...".

Line 238:
There seems to be a grammatical error w.r.t. to "waveguide".

Line 341:
There seems to be an "a" missing in "... by corrugated ...".

Author contributions:
I would appreciate if an overview of the individual authors' contributions is added.

Author Response

Thank you for the review.  There were many grammatical corrections made in the revision - specific to your review here is a list:

Fig. 1 graphics edited 
Added comma on line 176
Added comma to footnote after line 201
Added apostrophe to line 227
(no edit) I do not see a grammatical error on line 238
Made "waveguides" plural on line 342

Regarding "individual author contributions" this is an entry in the template but since this is a review paper I didn't think it applied here: the authors cited in the references serve that purpose.

Reviewer 4 Report

Review of "Overview of High Power and Wideband Radar Technology Development at MIT Lincoln Laboratory" by Michael MacDonald, Mohamed Abouzahra, Justin Stambaugh.

This paper is an informative and interesting summary of radar development at MIT Lincoln Laboratory, and a valuable contribution to the literature related to the radars used for studies of the atmosphere, geospace, the solar system, and man-made objects in those regions.

--- Comments on the text

38
> As a Federally-funded Research and Development Center (FFRDC) Lincoln Laboratory prioritizes the prototyping of advanced technology for national security.  The focus of this review ...

There is a discontinuity in the flow of the text between the previous paragraph and this one.  Perhaps something like:

=> In 19XX Lincoln Laboratory became a Federally-funded Research and Development Center (FFRDC), prioritizing the prototyping of advanced technology for national security.  That priority is manifested in the history of the laboratory's radars.  The focus of this review ...

44
> radars operating from UHF (435 MHz)

Why is this radar not in Table 1?

Is this radar the same as the MHR mentioned on line 41 ("Millstone Hill Radar (MHR) as a UHF prototype")?  Either way, it should be clarified.

45
> with both narrowband tracking and wideband tracking and Inverse Synthetic Aperture Radar (ISAR) imaging modes of operation.

Does "both" refer to narrowband and wideband, or to tracking and ISAR imaging?
Perhaps eliminate "both", and the first "tracking":

=> with narrowband and wideband tracking and Inverse Synthetic Aperture Radar (ISAR) imaging modes of operation.

50
> owing to the capability of these radars frequently providing insight

Perhaps
=> owing to the capability of these radars to provide insight

51
> on employing the radar as an instrument to investigate

Isn't it several radars?  Perhaps
=> on employing the radars as instruments to investigate

55
> A more detailed accounting of technology development in these radars is expanded upon in the next section.

Perhaps
=> A more detailed accounting of technology development in these radars is given in the next section.
or
=> The technology development of these radars is expanded upon in the next section.

64
> The Millstone Hill Radar was first constructed as a UHF (440 MHz) radar in 1956 to aid acquisition of BMEWS radar systems that were

Perhaps
"aid acquisition of BMEWS radar systems that were"
should be
"aid in development of the BMEWS radar systems that were"

Or otherwise clarify how constructing a radar would help in the purchase of the BMEWS radars.

73
> In 1965 Millstone was reconfigured as an L-band (1.295 GHz) radar with a new transmitter [3] and a 12-horn tracking feed [4] it retains to this day. Simultaneous L-band and UHF tracking of satellites led to order-of-magnitude refinements in metric calibration at Millstone which have since been implemented at other radars.

This is confusing -- was the radar reconfigured from UHF to L-band, or was L-band added, making it a dual-frequency radar?  

78
> The microwave configuration of the antenna is little changed since its conversion to L-band in the mid-1960s although the UHF feed has been removed and the UHF transmitter now serves two different antennas (one fixed at zenith, one steerable) are operated by the MIT Haystack Observatory Atmospheric Sciences Group.

Still confusing -- were the simultaneous L-band and UHF measurements made using two different antennas i.e. the original UHF now L-band Millstone antenna, and a different steerable antenna operating at UHF?  Please clarify.  

Please be more specific about the timeline, for example,

=> The microwave configuration of the antenna is little changed since its conversion to L-band in the mid-1960s, although the UHF feed was removed in 19XX, and since 19YY and 19ZZ the UHF transmitter has served two different antennas (one fixed at zenith, one steerable, respectively), operated by the MIT Haystack Observatory Atmospheric Sciences Group.

Note that, in the original text, "are operated" is a typo.

There is a bit of confusion also in regard to the name "Millstone Hill Radar".  The three antennas mentioned all claim the Millstone name, and all operate as radars:

https://www.haystack.mit.edu/the-millstone-hill-geospace-facility/
https://www.haystack.mit.edu/about/haystack-telescopes-and-facilities/millstone-hill-incoherent-scatter-radar/

So at least in a casual sense all three might be referred to as the Millstone Hill Radar.  Perhaps this can be clarified in some way, perhaps something like an addition to the above suggestion:

... operated by the MIT Haystack Observatory Atmospheric Sciences Group and known as the Millstone Hill Incoherent Scatter Radar [reference].

Note also hyphenation rules.  The text should be
"conversion to L band in the mid-1960s"
where "band" is a noun,
but "L-band antenna" is correct, where "L-band" is a compound adjective.

Similar corrections could be made in other places in the manuscript.  See
https://www.grammarbook.com/punctuation/hyphens.asp

107
> Irwin Shapiro conducted the 4th test of General Relativity at Haystack by measuring time-of-flight of pulses reflected from Venus as it passed behind the sun to quantify the effect of the solar gravitational field.

This is the only case in the manuscript where a person is mentioned rather than a reference.  Perhaps rewrite and include Shapiro as a reference, for example:

=> The fourth test of General Relativity was conducted at Haystack, by measuring time-of-flight of pulses reflected from Venus as it passed behind the sun, to quantify the effect of the solar gravitational field [ref Shapiro].

227
> upgrades through the radars history.

Perhaps
=> upgrades throughout the radar's history.

230
> MMWs Ka-band system

=> MMW's Ka-band system

234
>  Varian (now CPI)

What does CPI stand for?  Is it Communications and Power Industries mention in line 295?  But please specify it here rather than later.

239
> A novel quasi-optical beam waveguide feed was implemented [28]

Perhaps something like
=> In 19XX, a novel quasi-optical beam waveguide feed was implemented [28]

262
> Lincoln laboratory

=> Lincoln Laboratory

269
> This upgrade doubled the image resolution and tracking range of the radar. The tracking range window more than tripled.

What is the tracking range window (which tripled), vs tracking range (which doubled)?

Is the tracking range the maximum range that the radar can image objects, or something else?  

The image resolution must depend on the range.  The way it is phrased, it sounds like the image resolution doubled at twice the range, but it is unclear.  Is the resolution dependent on the bandwidth, and the range dependent on the power?  Please clarify in the manuscript.  

A few additional words, specifying which part of the upgrade resulted in which improvements, would help clarify.

316
> support net-centricity needs for networked Department of Defense (DOD) needs.

Redundant "needs".

323
> 8 GHz bandwidth

Should be "8-GHz bandwidth".  See for example:
https://www.grammarbook.com/punctuation/hyphens.asp

The hyphenation rules might also be considered on line 327:
> in the 92 – 100 GHz band
and throughout the manuscript.  

430
> to 50 Watts or more

The unit name "watts" is not capitalized, see for example:
https://www.nist.gov/pml/owm/writing-si-metric-system-units

Also on line 433:
> a 20 Watt peak power module

should be
=> a 20-watt peak power module

where the hyphenation rule mentioned above (line 323) also applies.

475
> Space Force.

This is for publication in an international journal.  The U.S. Space Force, rather than just the Space Force, should be specified.  

Similarly, on line 496, the U.S. Department of the Air Force should be specified.

486
> While the bulk of synoptic work is handled by optical sensors, it is the role of radar, particularly at long ranges, to obtain details beyond the trajectory of these objects.

Why is it "beyond the trajectory" instead of "including the trajectory"?  As least in some applications, radar is especially good at quick and accurate determination of orbits.  


--- Comments on the Figures and Table

In general, the figure captions are overly minimal.  It would add interest and comprehension include additional explanation and information in the captions.  Many readers skim the text and read the captions.  Interest generated from interesting captions will increase an overall positive impression of the paper.  There is no harm in repeating some information in the captions that is also included in the text.

Fig 1

All of the text in the graphic is significantly smaller than in the manuscript, and much of it is tiny.  The size of text within the figures should be comparable to, and not significantly smaller than, the manuscript font.  

Fig 3
> The figures pictured near the subreflector provide a human scale.

I don't think those are human figures.  The detail is so tiny and grainy even the authors can't see it clearly!  Improvement would be welcome.

Fig 5
> The generation of a range-doppler image from a time series ...

The steps should be explained.  The small text should be larger.

Fig 6

The two panels should be identified, e.g. "The Skylab space station and a simulated ALCOR image".  The text in the second panel is redundant with the caption.  The colors in the second panel should be explained in terms of range and doppler.

Fig 9 and Fig 10

These figures are a bit too small.  The figures should be as informative as possible, and should not be more difficult to read than the manuscript text.

Fig 13

The two panels should be clearly separated so that it is obvious that there are two panels.  The bottom panel perspective is a bit confusing and should be explained.

Table 1

Table 1 is "A summary of the parameters of the radars described here, in order of frequency" but not all radars are included, and the summary could be more informative.

Specifically, to help the reader keep track of the radar systems and the development work, the first column should include the location and the years of operation.  

Wasn't the MHR originally also a UHF radar at 435 MHz (mentioned in the introduction)?

The frequencies of the Cobra Gemini - S and X should be included, rather than simply "S band" and "X band".

Fig 15
> one of two Klystrons

=> klystrons

Fig 16

The graphics are so small, and the lines so faint, that it is difficult to see that the selective surface and metal bullet are enlargements of the feed mechanism.  The text in the figure is less than half the size of in the manuscript.  I suggest doubling the size the of graphics, stacking the panels vertically instead of horizontally, and making certain that the lines are clearly visible.

Fig 18

Only one thing is mentioned -- the cryogenic latching-circulator receiver protector -- yet there are two panels with no apparent relation between them.  Improvements for clarity, and the figure and/or the caption, will be helpful.

Fig 19

The top and bottom lines of text in the figure, i.e.
"Unclassified compact-range ..."
and
"ALCOR (1973) is omitted ...",
would be better incorporated into the caption.  

In the bottom line on the figure, please clarify what is meant by "(1973)" -- is it an unreferenced reference?

It would be interesting to the reader, and for the general interest of the article, to indicate what type of technology improvement was responsible for the improvement in imaging resolution shown in the successive examples.  Some appear to be due to an increase in frequency, and therefor shorter wavelength, but MMW, MMW2, and MMW4 have the same center frequency.  

I don't see how the improvement in range resolution could contribute to the improvement in imaging resolution.  Range resolution is dependent on the coding baud length, which improves proportionally with bandwidth, as can be seen in the table.  And range is along the beam.  I have been assuming that the imaging being discussed is primarily across the beam, is that correct?  Perhaps this should be explained in the caption or in the text.  

Perhaps the imaging resolution is improving due to improved signal-to-noise, perhaps due to improved power density, i.e. increased transmitted power or perhaps improved antenna gain.  If so this should be indicated.  However, in the text it says "Figure 19 ... illustrates the progress made in leveraging increased operating frequency and bandwidth to obtain progressively higher image resolution."  Given that, it would be reasonable to explain how the increase in resolution was achieved from MMW to MMW2 to MMW4.  

Fig 21
> The numbered annotations show significant fragmentation events due to collisions in space.

There are only three numbered annotations.  Perhaps they can be identified in the caption.  I think one of them, for example, must be due to the Chinese anti-satellite test of a few years ago.  

Please see English language comments included above as part of Comments and Suggestions for Authors.

Author Response

Thank you for your review.  A list of responses to the requested edits is below.  I think I've resolved the grammatical issues but a few may linger.

(GENERAL: need to correct hyphenation)

38 (no edit) style issue - we are simply introducing the mission of an FFRDC lab
44 Agree we have tried to work MISA in because it is confusing - a reference to J. Evans paper introducing the topic was added
45 Rewrote sentence to clarify
51 Edited per request (good catch)
52 Edited per request
55 Edited per request
64 Rephrased to accentuate that Millstone was a BMEWS prototype/pathfinder
73&78 Rewrote UHF & Tied to MISA & zenith antenna operated by MIT Haystack ASG (added an ASG reference)
107 Added Shapiro reference
227 Corrected missing apostrophe
230 Corrected missing apostrophe
234 Identified CPI as Communications and Power Industries and condensed later mentions to "CPI"
239 Added date
262 Corrected
269 Clarified paragrap
316 Corrected: good catch
323 Hyphenation corrected
327 Hyphenation corrected
430 Corrected - I did my graduate work at NIST and I should know better :)
433 Corrected
475 Corrected
486 This sentence has been rewritten to clarify the point raised in the comments on Figure 19: optical and radar sensors are complementary for imaging of space objects.  The former has a 1/range^2 SNR dependence and a 1/range resolution dependence.  The latter have a 1/range^4 SNR dependence, but as long as the SNR is high enough for a good quality track the imaging resolution is range-independent.  As a result, for low Earth orbit radars are used for synoptic scans and optical sensor provide imaging, and at deep-space orbit optical sensors provide synoptic scans and radar sensors provide imaging.
496 No edit: the lawyers wrote this!
        
FIGURES GENERAL: We were limited (by sponsors) to previously-publicly-released graphics so some comments cannot be rectified
Figure 1 has been enlarged and timeline edited
Figure 3 is an artist's impression - a slightly clearer figure was found but the two figures near the subreflector are human scale
Figure 5 has been simplified and the text enlarged.  The caption includes a brief description of the process
Figure 6 has had the redundant annotation removed from the simulated image and the two panels are identified in the caption.  We do not have access to the colorized scale of the simulated graphic - it is shown for qualitative purposes
Figures 9 and 10 have been enlarged
Figure 13 has had a space added to separate the panels and a description of the two panels has been added to the caption
Figure 15 has had the caption corrected
Figure 16 has been enlarged
Figure 18 has expanded the caption to better explain what is seen
Figure 19 has had its caption clarified to explain how image resolution is being increased.  The process was illustrated in Figure 5 - we use linear-frequency-modulated (LFM) waveforms which are Fourier transformed to produce bandwidth-dependent range resolution.  Integration time is chosen to match Doppler (cross-range) resolution to range resolution.  The impact of SNR is on the operating range of the radar for a given target RCS.
        

Reviewer 5 Report

The paper provides a comprehensive summary of over 60 years of radar system development at MIT Lincoln Laboratory. It covers the evolution from early satellite tracking and planetary radar systems to advanced capabilities like centimeter-resolution imaging of space objects. Key topics include radar technology, tracking, and debris management. The document also discusses various radar systems and their advancements, including Millstone Hill Radar, Haystack Planetary Radar, and others, highlighting their significant contributions to radar technology and national security.

Based on the article's content, here are two suggestions for improvement:

Include Comparative Analysis: Compare the radar systems developed at MIT Lincoln Laboratory with other leading systems worldwide to contextualize their significance and advancements.

Discuss Future Implications: Elaborate on the potential future applications and developments of these radar technologies, especially in areas like national security or space exploration.

The paper provides a comprehensive summary of over 60 years of radar system development at MIT Lincoln Laboratory. It covers the evolution from early satellite tracking and planetary radar systems to advanced capabilities like centimeter-resolution imaging of space objects. Key topics include radar technology, tracking, and debris management. The document also discusses various radar systems and their advancements, including Millstone Hill Radar, Haystack Planetary Radar, and others, highlighting their significant contributions to radar technology and national security.

Based on the article's content, here are two suggestions for improvement:

Include Comparative Analysis: Compare the radar systems developed at MIT Lincoln Laboratory with other leading systems worldwide to contextualize their significance and advancements.

Discuss Future Implications: Elaborate on the potential future applications and developments of these radar technologies, especially in areas like national security or space exploration.

Author Response

Thank you for your review.  We have added a paragraph at the end highlighting activities by other organizations and discussing future mission trends in radar.  Because this review was focused on our activities we admittedly make a limited effort to compare/contrast our activities with those of other organizations.    We were also limited (by sponsors) to discussing activities already in the public domain.

Reviewer 6 Report

The expression of the paper is clear and the logic is rigorous, and provides a good explanation of Lincoln Laboratory's research on High Power and Wideband Radar Technology Development.

Author Response

Thank you for your review.